Perennials self-seeding at Pensthorpe.
Traditionally, the way plants were organized in parks and gardens reflected a culture that liked to order and discipline nature. Contemporary planting design is not only freer, but also seeks to reflect nature. It also addresses our concerns about how we garden sustainably and in partnership with nature.
Even someone who takes the quickest glance at a wild or semi-natural habitat will see that it is a blend of different plant species. Someone who has no interest in wild plants and lives most of their life in a city standing in front of an average field in spring or early summer – by which we mean a traditional low-intensity pasture or hay meadow – will rapidly appreciate that several different kinds of wildflower are present, and that they are all mixed up. Ask them to pay a bit more attention to the grass, and they will soon appreciate that more than one kind can be seen; some in the field form obvious tussocks, others which appear to be spreading on to some bare ground are particularly fine, whereas still others just seem to form an even-textured mass. The flowering plants present (in Europe, most likely to be meadow buttercup, Ranunculus acris, and red clover, Trifolium pratense) are scattered all over the field but not evenly – clearly in places the concentration of flowers is greater than in others. Areas of abandoned agricultural or other land can be even better sites to appreciate this complexity of plant life. In much of North America the diversity can often be visually very impressive, particularly later in the growing season, with a range of grasses, wildflowers and wildflower seedheads scattered across a wide area.
Early spring is a very good time to appreciate the layout of perennial combinations. In the planting above (top) species are in blocks – although most designers would not plant out in straight lines like this (carried out here by the New York City parks authority). The planting above (bottom) shows a more naturalistic intermingled style (on the High Line) – blocks may still be used, but they are more likely to bleed into each other and some plants are more scattered.
Looking at a semi-natural grassland is a good place to start thinking about the visual qualities of natural plant communities. Similar patterns occur in woodland, but we famously cannot see the wood for the trees and a good vantage point can be hard to find. Thinking about what we are looking at, it is helpful to focus on the following qualities:
A prairie in flower is a good place to appreciate the patterns of plant distribution. Here several grasses stand out through their form, pale purple Physostegia virginiana and cream Parthenium integrifolium through their color, and gray Amorpha canescens through both color and form. The scattered and intermingled mixing of the species here is very typical of wild plant communities. This is Shoe Factory Road Prairie, Illinois, very near Chicago’s O’Hare Airport, in August.
Seedheads of Echinacea pallida indicate a loose group of the plant in prairie on a sand and gravel moraine at Glacial Park, Illinois, in September. Such occasional scattering can be dramatic and is easily replicated in cultivation. In the background a colony of Rhus typhina can be seen slowly colonizing the grassland – this small tree is used on New York City’s High Line, where annual pruning prevents it spreading too much.
MODERNIST MONOCULTURES – PLANTING IN THE TWENTIETH CENTURY
We are all familiar with most cultivated plants being grown in blocks. Arable farming does it on a huge scale, and the sight of a Brueghel painting of medieval peasants harvesting wheat reveals that it has always been so, only the size of the field varying with time and place. A great deal of the landscape planting with which we are familiar is composed of blocks, usually of shrubs, while much of the conventional advice about gardens of the average suburban size was to plant in groups of odd numbers. This convention of monocultural block planting is very much a creation of the twentieth century.
The dominance of the monocultural block as the basic unit of planting in public landscapes and to a lesser (and, needless to say, smaller) extent in private gardens can possibly be seen as a way of simplifying the cost of labor. Much nineteenth-century planting was very complex, requiring considerable time and skill to design and maintain. More informal planting styles which were developed by designers such as the English Gertrude Jekyll (1843–1932) used drifts – elongated blocks which were soft at the edges and allowed plant partnerships to be seen and appreciated from a variety of angles. Informality and simplification can be seen as the two dominant but linked trends throughout the twentieth century. Organically shaped blocks of perennials in post-war German public planting and much larger blocks with a clear link to mid-century abstract painting in the work of the Brazilian Roberto Burle Marx (1909–1994) illustrate the influence of modernism. Landscape shrubs in blocks in public places were widely used in the Netherlands in the 1960s, a trend in the landscape profession which proved very influential.
Modernism offered a rationale for the simplification and informality of much twentieth-century planting design. It failed to convince everybody, however. From the 1970s onwards, more ecologically focussed gardeners began to promote the use of native plant species and the idea of the garden as a biodiversity preserve – a Dutch group dedicated to these aims took the name Oase (oasis). This same period saw the maturing of a movement in Germany dedicated to creating plantings in public spaces through the development of a naturalistic and wildlife-friendly style. This German style, which has come to be known as Lebensbereich (habitat), is most chiefly associated with Professor Richard Hansen of Weihenstephan, a complex of trial gardens, research institutes and a university north of Munich; its roots lie in a plant ecology science strongly focussed on the study of plant communities. The most recent developments in this perennial-based planting style are on the creation of randomized planting mixes, which are discussed later in this book.
This garden in western Ireland (2006) uses block planting. However, plant groups are repeated so there is a strong sense of rhythm and unity; here, in July, these include Veronicastrum virginicum (center), Sedum ‘Red Cauli’ (right foreground), Molinia ‘Moorhexe’ (center foreground) and Helenium ‘Moerheim Beauty’ (right). In addition, clumps of the very tall grass Stipa gigantea stand above the rest of the planting and help tie it together.
Repeated single-species blocks of grass Deschampsia cespitosa ‘Goldtau’ create great impact on the large scale at Berne Park, Bottrop, Germany (2010). In the foreground, mixes give more interest; here are grass Sesleria autumnalis and Sedum ‘Matrona’. This is August.
The single-species block may be dated, but it should not be written off. It has an undeniably simple graphic quality which may often be regarded as valuable, particularly by professionals working in public environments. In private gardens and other intimate settings, its simplicity may be an advantage as a counterpoint to complex perennial-based planting schemes. In fact, its real value may lie as a counterpoint to the very focus of this book: intermingled plantings may not always be strong on structure, or they may lack structure at certain times of year; the use of firm monocultural blocks may create an exciting creative tension.
In situations where maintenance is limited by lack of time or skill, the advantage of monocultural blocks is very clear, as anything which looks different can be weeded out. This is particularly useful in the case of grasses. Many of us who have been busily promoting naturalistic planting and grasses over the years have been brought up short by situations where carefully chosen specimens are dug out or sprayed with herbicide because inexperienced or badly briefed staff have mistaken them for weed grasses. The unfortunate fact is that, early in the year, even many gardeners who are familiar with grasses can sometimes find it difficult to know which is a desired and which a weed grass. However, by putting grasses into monocultural blocks, it is much easier to avoid such tragedies.
For the most part, however, unless there are clear design, practical or functional reasons for block planting, we would strongly urge gardeners and designers to do their best to move away from this outdated and unimaginative style. In private gardens it simply acts as a deterrent to developing more creative planting schemes, while in the public realm it is little more than a crutch for those in the landscape profession who have for far too long treated plants as green cement. The exception might be the dramatically big block planting, which can have real design impact, but that is another story.
There are more important and more objective arguments against block planting than that it is boring and out of date, however. One is that, like a great actor drunk in the bar after a performance, a whole mass of one plant can look very dreary when it has finished performing. The fact that only a relatively limited number of perennials in the short to medium height range look at all respectable after flowering has meant that a few species tend to be seen again and again. One of the great advantages of Gertrude Jekyll’s drifts was that it made it much easier to hold on to a form of block, but by stretching them out she made it easier to hide plants with a ‘past the sell-by date’ look.
The advantage of intermingling plants over block planting is that random close juxtapositions of species are created. As autumn blurs into winter, these will revolve around the silhouettes, textures and forms of plants. Here, in a dry prairie planting at Hermannshof in Germany, grasses (with Nassella tenuissima prominent) combine with perennial seedheads (the dark heads are Echinacea pallida and E. paradoxa). The grayish seedheads to the right are subshrub Amorpha canescens.
Chance, or serendipity, should always be allowed to play a part in garden design, and even perhaps in the public landscape too. Here, an unexpected ‘meadow’ has sprouted over the years in between the paving blocks of a terrace on the south side of the Oudolf family house. Grass Nassella tenuissima, a short-lived but strongly seeding species, has germinated alongside purple-blue and pink seedling forms of Salvia pratensis, while the questing roots of Euphorbia cyparissias have sent up shoots between the pavers.
GETTING THE BLEND RIGHT – THE ADVANTAGES AND DISADVANTAGES OF INTERMINGLING
Moving from planting in blocks to blending, intermingling or mixing – all three words can be used interchangeably – is a major shift in planting design. A working definition would be to say that a ‘pure’ blend is a complete mixture of individuals of all the species used in a given area. This should not be too much of a challenge for gardeners and designers with good plant knowledge. For some time now, the idea of ‘plant combinations’ has been an important driver for creativity among both designers and amateur gardeners. A really good combination should have an electric quality about it – two or more plants where a particular complementary relationship of color or form sends the sparks flying. The reality is that these combinations are relatively few. Instead, a great many others are good but not outstanding – particularly useful are those more low-key combinations which look good over a long period. Simply taking a good combination and then repeating it is the first step in developing an effective intermingled or mixed planting. While two plants together can be dramatic, as a design concept it lacks depth and rarely looks good all year round. Combining four or five plants can create a simple mix, which if chosen well can provide interest for much of the year.
Here, where we discuss intermingled plantings, it is important to emphasize that there are two very different approaches. One is to carefully research a blend and then use it over large areas, either mixing the component plants at random or repeating a designed block, in the way that a mosaicist or tiler laying out a series of small modular units repeats it again and again to create a pattern. There is an analogy with a tea or whisky blender who works intensively on a small quantity of a blend, with an eye to mass production of their eventual choice. Such a planting blend can then be reproduced in two ways, one as literally mass production, with the mix being used anywhere conditions are suitable. Alternatively, it might only be used for one project: a site-specific mix. The other approach is not to randomize or repeat modules but to design in the location of every plant, to intermingle different combinations in different places, so allowing there to be small groups, repetitions at various frequencies and subtle transition effects.
To summarize, there are three approaches to blended planting here:
Of course, there are also ‘halfway houses’ such as blurring the edges of block planting or randomly scattering different species through a block planting.
Any gardener will quickly be able to suggest that sowing a seed mix is one way to achieve an appearance of randomness. Indeed, this is the approach which James Hitchmough of the University of Sheffield uses. The ‘Mixed Planting’ and ‘Integrated Planting’ systems developed in Germany and Switzerland aim to achieve a similar effect by using young plants. Modular repetition is technically difficult to achieve but is possible, and could in theory be used to create some highly effective plant juxtapositions.
Blended plantings are undoubtedly very beautiful and highly effective visually. This alone is an important reason for using them. They also have the advantage that it is possible to easily mix together species which flower or perform at different seasons. They are also forgiving of weed infiltration. As a general rule, the more ordered a planting is, the more problematic weeds are – one weed in a highly geometric bed of summer annuals stands out like a beacon. In wilder, more naturalistic planting styles, occasional weeds stand out less, while intermingled styles have the greatest capacity to absorb intruders. In fact, it is possible to take a pragmatic view and allow some spontaneously occurring species to survive and spread within the planting.
Finally, the advantage of the cost of mixed planting styles, or to be more precise randomized or sown plantings, needs to be considered. One of the reasons for the development of the German and Swiss planting mixes was to reduce the costs of large areas of planting for local government, garden shows and other public sites. The idea is that a mix is developed using careful plant selection, with both practical and aesthetic criteria, and so the design cost is all absorbed at the beginning as a one-off. Anyone can then buy the mix for as many hundred square meters as necessary, with seed or plant costs potentially carrying a percentage royalty for the original design team. The decision of the garden or landscape designer is limited to specifying which mix to use. Design costs are therefore minimized.
It is now time to consider the disadvantages of mixed planting styles. The widespread use of a limited number of planting mixes could rapidly turn them into clichés, much as sedum roofs have become. The fact that commercial nurseries are now marketing planting mixes could well result in a situation where a bold innovation, followed by a mass usage, will then become a boring lowest common denominator. The biodiversity value of such plantings could be good, but to earn popularity with the human element of the landscape – who, after all, select and pay for them – they must also offer visual quality. It is to be hoped that randomized plantings will be an area of continuous research and development, so that new combinations will constantly offer change and novelty. Commercially developed randomized planting mixes may be tailored to particular habitats, but these can only ever be crude approximations to the existing conditions where they are used. They are in no sense ‘site-specific’.
There is one other possible problem with randomized mixes, particularly those that are planted rather than sown. This is to do with long-term development and the distribution of species. In nature, plant communities are never random. Certain plant species will colonize an area first, followed by others, so the process of community development is cumulative over time rather than the entire community starting off at once – which is what happens if one is planted. Over time, slight differences in soil and microclimate conditions will cause species to select out, so that there are greater and lesser numbers of different species in different areas. Think about how wildflowers are scattered in a meadow or prairie; part of the visual pleasure is not just the scattering and mingling over a wide area, but the subtle ebb and flow of particular species over space in ever-changing combinations. If species are introduced by sowing, the slight differences in microhabitat will be registered very soon by the developing seedlings, so the mix will grow to fit its landscape. The result will be different trajectories of development in different places, leading to a good ecological fit to the conditions and visual diversity. The danger with randomized planting is that this will not happen, and in particular that species with a strong tendency to dominance will tend to dominate everywhere, and conversely less dominant species may be forced out everywhere. Just such problems have been observed in randomized tree plantings.
Modular repetition or designed intermingling of plants is a way of getting around this problem. Piet Oudolf’s work is undoubtedly a strongly designed intermingling; a mathematical analysis of his planting combinations would surely indicate an almost infinite number of potential species juxtapositions and combinations. Because of this, the long-term development of an Oudolf planting may be more akin to a naturally occurring plant community than a randomized planting. In addition, the number of species he uses is considerably greater than the 15 to 20 in most randomized mixes. Another aspect of Piet’s work is that his mixtures for larger areas are often of mingled groups of plants, of 5 to 11 individuals of each species (depending on the overall scale), so that the blend is in fact a blend of small groups.
Designers of the future will no doubt find ways of introducing greater visual richness and possibilities of future development into mixed plantings. In particular, decisions have to be made: whether to randomize, or to design mixes of small groups, or to go for small groups and individuals. Different decisions will be made for different plants and for different situations. Gardeners and designers are only at the very beginning of a whole new and immensely rich seam in planting design. Meanwhile we suggest that the thinking outlined in this book will help with this process.
Perennial growth by itself can create an effect of intermingling, either through the way in which species with fine branching and spreading stems can knit together or because of seeding. Here, in August at Hummelo in the Netherlands (left), a variety of perennials in small groups are beginning to mesh together, an effect heightened by the similar color palette of many of them. Pale Lythrum virgatum occupies the center, with deeper Stachys officinalis to the right. Behind and in front are the narrow spikes of Liatris spicata. Paler pink spikes belong to Sanguisorba menziesii. To the rear are the pale pink flowers of Sidalcea oregana.
At Pensthorpe Gardens in Norfolk, England (right) two species are beginning to blend to form a meadow effect, several years after being planted in separate blocks: Scabiosa japonica var. alpina and deep pink Dianthus carthusianorum both have fine stems which in nature wend their way through grasses; they can also be effective at seeding themselves.
CREATIVE TENSIONS – BALANCING ORDER AND DISORDER
For the vast majority of garden history, gardening and landscape management have been about exerting order over nature. This was understandable in a world where nature was seen as all-powerful and not necessarily benevolent. Now, the feeling is that nature is very much in retreat in the face of an aggressive humanity – exerting order is no longer seen as always appropriate. Previous generations tended to be highly anthropocentric: to see humanity as central to the world, and therefore the imposition of what we see as beautiful or useful on to the natural world as entirely right. Now, we have come to realize that we are only a recently evolved species on an insignificant planet, and a scientific understanding of our surroundings has largely knocked us off our pedestal. While we still want our planted landscapes and gardens to conform to our ideas of beauty, we are far more prepared to accept what occurs naturally as visually pleasing. Indeed, earlier forms of imposing aesthetic order on nature are seen by some as unattractive; so highly rated now is natural as a virtue that simply describing them as unnatural implies they are undesirable.
The further away from a natural situation a planting is, the more work is required to maintain it – hence the need to clip hedges and topiary every year, and in the case of fast-growing plants, two or even three times a year. It is no surprise that so much gardening in the past was about clipping – it was, and still is, a way of showing that you were able to afford to pay people to do this work for you. It is also about control – we want to control nature and the garden is a place where we show it. The cost of maintaining plantings which emphasize human order, and a growing relaxation in our relationship with nature, are additional reasons for the greater tendency over time to appreciate the beauty of nature’s apparent disorderliness.
The growth of interest in natural looking plantings has gone through several phases. Each of these has left a legacy of ideas about what is appropriate to call natural or not – sometimes these are contradictory. For example, the eighteenth-century English landscape garden introduced the idea (revolutionary at the time) that the straight line was not only unnecessary but undesirable. There is still strong resistance to straight lines among many who favor natural style gardening, yet an ecologist will point out that a bird does not mind if the tree in which it makes a nest is growing in a row of others or an informal cluster, and many designers will wax lyrical about how straight lines can add a sense of order and intention to otherwise wild-looking plantings.
In Britain, the Arts and Crafts garden tradition exemplified by Lawrence Johnstone’s Hidcote (1907 onwards) and Harold Nicolson and Vita Sackville-West’s Sissinghurst (1930 onwards) resolved a central contradiction for British gardeners, balancing their love of informal planting (mostly herbaceous perennials) with a continued hankering after formal garden features, now restricted to hedges, occasional topiary and garden structures. In the Netherlands, Mien Ruys (1904–1999) did something to achieve a modernist version of the same resolution of the conflict between formality and naturalism. For contemporary garden makers there is now a well-developed and richly nuanced range of possibilities for balancing the wildness of nature and the order of culture.
APPARENT DISORDER – THE PARADOX OF DESIGNING SPONTANEITY
The English landlords and their advisors who laid out landscapes with sinuous clumps of trees in the eighteenth century, and indeed all those who followed them, were trying to convince potential viewers, and almost certainly themselves, that what they were achieving looked natural. It is, of course, nothing of the sort, as nature would not tolerate the clear edges between woodland clumps and open grassland for very long, and would seek to clutter and blur them with seedling trees, shrubs and climbers, and eventually to reassert the wood over the grass. In addition, the clumps and their attendant lakes and fields were laid out to fit certain artistically derived ideas. Naturalism is so often a conceit.
Another naturalistic conceit, but on a different level, is the often spectacular plantings developed for garden shows in Germany from the 1980s onwards. These were laid out for one-off events but left behind quality planting for permanent public use. The designers were trying to create plantings which looked natural. They were in no sense pretending that they were imitating nature, but instead were seeking to group plants in such a way that the results had a natural look about them, and would no doubt convince many onlookers they were looking at something very much like the real thing. In the final analysis, though, decisions about which plants to group together, in what combinations and numbers, are aesthetic ones. The creators of what have come to be known as cottage gardens have achieved similar results, but through a completely different route. Margery Fish (1888–1969) and all those who have followed her in this genre had no illusions that they were creating anything ‘natural’ or indeed pseudo-natural. Their model was another conceit: that they were making something akin to what humble cottagers (rural laborers and their families) would make. Both traditions end up creating an apparently artless combination of plants which have proved highly popular. The spontaneity is, however, apparent rather than real.
The truth is that while much of humanity loves nature, people do not want it untrammeled in their gardens, parks or urban spaces. The stylized natures offered by the various cultures of planting design developed during the twentieth century are the most realistic ways out of this conundrum.
STATIC AND DYNAMIC PLANTINGS – MANAGING SPONTANEITY AND CHANGE
As combinations of living things, gardens will constantly change as they age. The traditional concept of the garden tended to be static – many of the planted features were clipped into shapes that recalled the masonry of the great houses of which they formed the surroundings; trees came and went on a cycle of several human generations – while ephemeral annuals and bulbs filled rigid parterres for a few months at a time. So for many gardens there were two extremes: an almost permanent architecture and short-lived seasonal planting, both requiring high levels of maintenance. Twentieth-century gardens reduced maintenance and formality by relying more on shrubs and perennials, which allowed for greater leeway in maintenance. They could often almost be ignored for a few years, brought back to order with a blitz of pruning, weeding and dividing, refreshed with a few new plants, and then receive a few more years of relatively unimaginative maintenance. The result was often functional but rather lackluster gardens of slightly unmanaged looking shrubs and ever-expanding clumps of a few robust perennials.
Over time, plantings based largely on perennials will age. There are two main aspects to this: some species will die out, whereas others will spread, some by simply creeping out from their original planting space, others by self-seeding. Less-skilled maintenance often only removes weeds, and does not seriously address either of these issues. In addition, slow spread can creep up on garden owners, and before they know it, the goldenrod (in old gardens derivatives of Solidago canadensis) and Japanese anemones (Anemone ×hybrida) have taken over. The result is chiefly a loss of diversity. The issues of vegetative spread, self-seeding and plant death are looked at later on.
Perennials, and to some extent shrubs, have their own life cycles of growth and replacement and spontaneously self-seed between different parts of the garden. This dynamism has been played with cautiously for much of the twentieth century, but now with a better understanding of plant ecology gardeners and designers are in a stronger position to work with spontaneity rather than resist it as ‘disorder’ in the way our gardening ancestors did. A key problem remains, though, the tendency to lose species over time and so lose visual diversity.
How much is lost over time from a planting depends very much on what was planted originally, in particular whether long-lived and robust species were chosen or not. During the early years of the twentieth century, the selection of perennials was dominated by short-lived species or those which were not very persistent. In the latter part of the century these were replaced with more robust and naturally long-lived or persistent species, often less intensively hybridized. At the time of writing, older parts of the Oudolf garden at Hummelo have hardly had any replanting done since they were laid out 20–25 years ago.
How long do perennial plantings last? And – what should be done when they need restoration? Two types of management can be envisaged: a low-key, relatively passive one, and a more active one, but which works very much with the naturally dynamic nature of the planting. A passive approach involves:
Even the best planned perennial-based planting will experience a decline in species diversity – highly persistent and the most vigorously self-seeding species will be the survivors. Cutting back annually and leaving the shredded debris as mulch or taking it away, composting it and returning it as mulch will keep nutrients recycled. Even if material is taken away and not returned, causing nutrients to decline slowly, growth will often continue to be very good for many years on many soils, as long-lived, persistent perennials do not have a great hunger for nutrients.
A more active involvement with the planting recognizes natural processes of death and rebirth: ecological processes, in other words. James Hitchmough and Nigel Dunnett at the University of Sheffield’s innovative Department of Landscape refer to this as a ‘dynamic planting’. Change and spontaneity are embraced. However, the planting will not look after itself. Engaging with a dynamic planting involves controlling and editing the outcomes of natural processes, steering the planting in a way which maintains or even enhances its appeal. We will look in more detail at how this can be done later. Key to managing a dynamic planting is understanding that perennials have a variety of life cycles.
However, even with the most skilled management, a point is reached when some sort of restoration becomes necessary. This is very difficult to predict, both because of the complexity of plant–environment interactions and because the perception of the planting is inevitably subjective. Ten years might be a good time if expectations and demands are high. What happens now? ‘Restoring’ is still favored by many, but this assumes a turning back: recreating how it was when first made. In the (for the sake of argument, ten years) since the planting was made, the following will have happened:
Exact restoration will almost certainly be inappropriate, and will often seem undesirable. Renovation might be a better word. New cultivars and ideas need to be taken on board, so that the original plants live on alongside newcomers, and the planting reflects the passage of time.
It is not entirely true that species diversity in plantings declines over time. Sometimes, attractive and not-too-aggressive wild species may appear and add themselves to borders. One such is the early spring flowering Cardamine pratensis (shown here in close-up), especially on damp soils.
Upright Verbascum leichtlinii is one of several species of a large genus of plants in a family (Scrophulariaceae) where a great many are either biennials or short-lived perennials. Survival is through scattering their plentiful seed to the wind from sturdy seedheads. Their advantage to gardeners is the spontaneity and naturalness of the way that they move themselves around the garden. Here, at Hummelo, in early June they flower alongside Knautia macedonica (deep red, foreground, a short-lived perennial). The combination of clipped yew hedge and self-seeding plants makes for a great expression of creative tension.
In the new perennial meadow in the Oudolf family garden at Hummelo in the Netherlands, perennials arise out of wild grasses and spontaneous flora, such as the wild chamomile (white flowers, foreground). Other species here are Agastache nepetoides (seedheads, left), Aster ‘Little Carlow’ (center), Aster novae-angliae ‘Violetta’ (right), and pink-red Eupatorium maculatum ‘Riesenschirm’ in the foreground, right.
Avenues are a traditional way of setting out landscape plants. A row of trees makes an effective backdrop to the apparent chaos of a late autumn border of grasses and perennials at Westerkade, Rotterdam.
THE HUMAN AND DESIGN CONTEXT
Planting has to please people – as has been said before, people are part of the ecology too. The point has been made by others that in order for natural environments to be valued by humans they have to be liked – simply functional plantings which satisfy technical criteria for sustainability or biodiversity but do not satisfy human users are in the long run doomed, because nobody will care for them enough to campaign for them when they are threatened by other potential users on this overcrowded planet or simply through lack of care.
The role of the gardener or designer is clear, and arguably more important than ever: planting which serves a purpose has to look good too. As practitioners use plant combinations more and more to perform environmental services, it will become increasingly important that they look intentional and attractive.
Tidiness and presence are important issues, although often read very subjectively. In corporate or memorial plantings, even occasional seasonal scruffiness is unacceptable. If there is no guarantee of labor to keep up standards, planting will have to be limited to species which can be kept acceptably tidy, although it is possible to include species which look unattractive post-flowering in large areas of mixed planting where there is enough structure to maintain the look of the whole. There is more scope for using less tidy-looking plants in more relaxed surroundings. This is an important point, as some of the most popular, easily propagated and resilient perennials do look bad after flowering. Keeping such plants to no more than an absolute maximum of 30 percent is a good rule, but even so, for some situations where such plants may grow very well and flower for long periods, gardeners and designers may feel they want to use more. Some such plants, certain Geranium species in particular being a good example, are also very long-lived and effective ground cover and can be tempting to use in large quantities in low-maintenance situations. The addition of just a few distinctive structure plants, or others with a different (usually later) flowering time, can do much to lift such a planting beyond a flat monoculture. Other possibilities are partial concealment by using them in drifts around more strongly structural plants or placing them where they can be enjoyed when they perform but do not detract from key vistas. These plants can often be managed more intensively for a higher quality look in smaller spaces, and of course in private gardens, where there is more possibility of managing them through seasonal cutting back.
Bright colors are popular, and can be entirely compatible with naturalistic or functional planting. This is Astilbe chinensis var. tacquetii ‘Purpurlanze’ in July, a robust and long-lived perennial eminently suitable for drainage swales and other sustainable drainage plantings. Its winter seedheads (overleaf) have great value.
During 2011 the Serpentine Gallery, a venue for contemporary art in London, hosted a Piet Oudolf planting in a courtyard. For the majority of the species used, the location would not have been suitable in the long term, but a summer-long show garden-type display was perfectly feasible. As with flower-show gardens, plants were used at higher densities than would be normal for a permanent planting, but one advantage (as show garden designers know only too well) is that the visual experience is more intense than in the real garden – this is, of course, useful in a venue such as this where onlookers are at very close quarters to the plants.
Temporary plantings do not have to be composed of garish annuals. Here, at the 2010 Venice Biennale, is a rarity – an Oudolf annual composition of Hordeum jubatum (wild barley) and dahlias. It playfully evokes the spontaneous plant communities of waste ground.
CONTROL OVER NATURE? – FORMALITY AND MASS PLANTING
Formal planting – the use of geometry or clipping to create unnatural forms – is widely seen as traditional. There are, however, many possibilities for a more contemporary approach. Novel forms of formality (such as non-symmetric clipped woody plants or blocks of ornamental grasses) are nowadays more likely to be seen as appropriate in larger and grander contexts than traditional, clipped and symmetric formality. Larger scale settings or those which need to look imposing require simple graphic qualities, which can be expressed through some kind of monocultural planting. Traditional materials like yew or beech can be given new life with modernist-inspired geometries. Ornamental grasses are the other great material for monocultural blocks, because of their relatively long season of interest, adaptability, longevity (for most species) and simplicity of form. An added advantage is that they take less maintenance than clipped foliage. Their disadvantage, vis-à-vis clipped woody plants, is that they do not have the same level of presence all through the year.
One of the great uses of any kind of mass planting like this is that it can contrast so effectively with highly complex and diverse plantings of perennials, giving architecture and backbone to what would otherwise be too visually soft-textured for some environments. It is worth considering here the global success of the English Arts and Crafts garden style. Fundamental to it is a balance between order and apparent disorder. Rather than relying on the old vocabulary of clipped woody plants, contemporary gardeners and designers should perhaps be looking at grass blocks to provide the structural part of the equation.
In corporate or monumental landscapes, simple blocks of woody plants with grasses may be all that is needed to create the atmosphere of calm, control and order. Where the general public is concerned, however, these words are more likely to have negative connotations, as many people have an expectation of planting providing life, vitality and color. Where the scale is large, as in public parks, it can be difficult for colorful and diverse planting to actually make much of an impact – or to rephrase this, there is rarely enough funding for plantings that really make an impact. The creators of randomized planting mixes and seed-sown perennial mixes (such as prairies) claim that their combinations can be maintained extensively – all plants attended to at once, mainly through mowing. This may well be the case, at least in some climate zones, but the concept is still too new for a long-term picture of their maintenance needs to be clearly understood. If maintenance can be kept low enough, then these plantings do genuinely offer an option for large-scale situations.
Molinia caerulea ‘Dauerstrahl’ in blocks. This is a native plant of acid soils across northern Europe, so its presence here in the Netherlands can be described as a novel use of a formal planting principle with a plant which actually relates to its landscape, much as previous generations might have had clipped hedges of native trees. This kind of simple, calm, ordered planting can be a good point of relaxation after an exuberant perennial-filled border – like the sorbet course in a gourmet meal.
NATURE OVER CONTROL – MAKING WILD-LOOKING PLANTINGS
Those who wish the plantings they make or commission to look tidy and ordered – ebullient nature controlled and organized for the human eye – stand in the majority tradition of garden history. The more recent tradition, which I see Piet Oudolf and myself as part of, is about the opposite – how to create the sensation of nature, often in urban or suburban areas. As we know all too well, this does not mean letting things go by allowing natural processes to take over. When people say they want some nature, what they usually mean is a particular vision of nature, one that looks nice, fitting in to a distinctly human-centered idea of what nature is or should look like. Biodiversity is important too (but not mosquitoes or snakes, of course!), and often locally native plants. ‘Nature Lite’ in other words. We must not be too cynical – not too long ago any idea of ‘nature in the city’ would have been anathema or at least incomprehensible to most people. The task for the gardener or designer is to create an enhanced nature (a term coined by Nigel Dunnett and James Hitchmough), one that supports an acceptable level of biodiversity and looks just a little bit wild. How can this be achieved?
In a public setting much of the above is about getting people to read something subconsciously, and the people concerned will for the most part have very little real knowledge or experience of natural plant communities. What matters to them, what will convince them and enable them to read the designed planting as some kind of ‘nature’, is that it evokes the country park or nature reserve or state forest or wherever it is that urban and suburban people in a particular place experience nature. The New York High Line is a good recent example of this kind of planting. The world’s oldest established and most extensive examples are the parks of Amstelveen in the Netherlands, dating back to the 1930s, where the planting is almost entirely native but is highly managed for a relatively neat appearance.
For homeowners who are only trying to convince themselves and their family and guests, the hardest task is probably to convince themselves that they have built and planted a microcosm of nature. Gardeners or others who are interested in nature and know their wildflowers may be hard to convince. Most who do succeed often mix natives with garden plants, and have cultivated the art of knowing how much to let go.
Graphic simplicity is given an added boost through autumn color. Here, Rhus typhina, a suckering shrub which can be restricted through coppicing, grows alongside Calamagrostis ‘Karl Foerster’, a grass which is extremely useful for minimalist or ‘neo-formal’ plantings because of its long season (early summer to late winter) and its weatherproof, upright habit.
A distinct feature of the garden at Hummelo is the big clump of the grass Miscanthus sinensis ‘Malepartus’ in a slightly raised position, seen here through a haze of the seedheads of another grass, Molinia ‘Transparent’. The miscanthus block acts like a weight, a center of gravity for the garden as a whole, especially since it is more or less midway between two distinct areas of the garden, both dominated by looser perennial borders.
Wild and woolly, the High Line is dominated from late summer on by the seedheads of grasses – anything tidier here would look out of place next to the still scruffy areas of the urban jungle. The flash of orange-red is Iris fulva.
SIGNATURE PLANTING – DEVELOPING AN IDENTITY
The idea of signature is a strong one in the art world, the distinctive stamp of an artist or maker. Good garden designers have all developed a very strong signature, so that the knowledgeable could probably recognize one of their gardens if they were parachuted into one they had not seen before. Gardens too can develop a signature in the minds of those who visit them, because of some distinctive feature, or the use of a strong theme plant which is scattered throughout the garden.
While private gardeners who develop a theme for their garden which is endlessly admired and photographed by all who visit can sit back and pat themselves on the back, the problem for designers who develop a successful signature for a particular garden is that it becomes very difficult to reproduce elsewhere. The other problem is that everyone else copies you, and usually less successfully, perhaps even turning an innovation into a cliché.
Signature plantings are about making something that is site-specific and gives the garden or landscape a distinct personality which helps to make it memorable. This is clearly important for public landscapes, but home gardeners can try it too. One plant spread throughout a garden can make a real impact in the here-and-now but also in the memory of visitors. I have an immensely tall and narrow clone of Eupatorium fistulosum, which grows to 3.4 meters high every year; visitors to the garden in the late summer to winter period inevitably remark on it, and even American visitors are impressed (it is a US native). Over the years it has become the most commented on plant in my garden, and I am sure the most remembered.
Signature plantings may be derived from several sources:
The following Piet Oudolf projects exemplify what have become recognized as strong signatures in the garden and landscape press, or otherwise stand out for me as signature plantings.
This stylized meadow originally used Deschampsia cespitosa interspersed with a small number of contrasting perennials. Widely agreed to be a good idea at the time, it was copied by several other designers, generally unsuccessfully. One problem is that the species can die prematurely on fertile soils, and some cultivars are susceptible to fungal diseases and can suffer extensive dieback. Deschampsia has now been replaced by cultivars of Molinia caerulea, which, although also a plant of infertile soils, is longer lived across a wider range of habitats. This concept makes an impact in design terms and makes sense in management, and it can be emulated by using other grass species and therefore work in many different climate zones.
Conclusion – a signature might be a very good concept, but needs to be adaptable to be effective long term.
Piet’s use of a grass matrix in plantings started with what became a well-known new feature, the Deschampsia meadow at Bury Court (1996). The latest manifestation is a new planting on the former nursery site at Hummelo. Created through both planting and sowing, the species mix will change from year to year. Tall grass Calamagrostis ‘Karl Foerster’ and the scarlet cultivar of Helenium will be more or less permanent, but many other shorter-lived species, such as the two color forms of Verbena hastata and Dutch native daisy Leucanthemum vulgare, will be dependent on self-sowing for their continued existence here.
Thirty-three bands of intermingled perennials and grasses, each of equal size, line either side of a straight grass walkway. Looking very formal and rigid on paper, it is anything but in practice. A good example of a simple design concept which underlies an entire scheme, but largely succeeds in hiding itself so that perhaps comparatively few people have really understood it.
Conclusion – strong signatures are sometimes almost invisible, operating on the level of the subconcious.
The double border at the RHS Garden, Wisley (2001), where bands of intermingled perennials create interesting combinations at all scales of observation, from near to far. In mid- to late summer Perovskia atriplicifolia dominates (above), counterposed with pink Gaura lindheimeri ‘Siskiyou Pink’ and the seedheads of Phlomis tuberosa ‘Amazone’, while in another band (below) gray-white Eryngium yuccifolium contrasts with scarlet Helenium ‘Rubinzwerg’ and Echinacea purpurea; some seedheads of Allium hollandicum survive from an earlier phase of flower.
The Salvia River is a band of three violet-blue cultivars of European origin. The public loved it – it had impact and the photogenic ‘wow’ factor that commissioners of such projects always want. Something so simple and dramatic is very hard to repeat, but Piet did so in the Lurie Garden in Chicago; as he describes it, ‘It was one of the few times that I really copied myself, it had to do with the graphical quality of the concept, it had to be seen from the surrounding skyscrapers.’ No one else has yet copied it or tried to achieve it using other species. One of the problems in doing so is that most colorful perennials in a low to medium height range have poor structure post-flowering (the salvias just look a bit dull, and can be cut back to repeat flower later).
Conclusion – there is always a danger that very strong signatures will be copied, but it is a risk worth taking.
Stipa gigantea is a tall and expansive but at the same time very light and transparent grass. Piet used it in gardens back in the 1980s and early 1990s, but when everyone started using it, he gave up on it. Here, however, just a few are used to spectacular effect; at a latitude of 51 degrees north, early morning and late afternoon sunlight striking this grass illuminates it to dramatic effect in this open site.
Conclusion – clichés can be challenged.
The multiple curtains of yew at the rear of the main garden area at Piet and Anja’s own garden became, in that much overused word, iconic. In the end, though, they succumbed to the forces of nature in the form of flooding which led to phytophthora disease and dieback, so early in 2011 they were removed and fed dramatically into a chipper. Piet phlegmatically accepted that it was in danger of becoming a cliché.
Conclusion – icons sometimes need iconoclasts.
The rear hedges of yew (Taxus baccata) at Hummelo became one of its best-known features. A classical material and idiom, their asymmetric cut and modernist flair deservedly made them a contemporary garden design icon.
After their removal, the garden is defined by a mix of hedging – a clipped but informal version of a traditional mixed farm hedge (on the left here) and more formally clipped beech hedging at the rear (only just visible).
It is perhaps the grasses on the High Line which make it so distinctive. Originally (that is, as an abandoned freight rail line), grasses were part of a rich species mix, so using them was part of the design intent to keep a strong sense of the original spontaneous planting. They certainly make the High Line the most naturalistic Oudolf planting so far, and add hugely to its character. Part of the appeal of the High Line is that it is so successfully brings nature into the city – the grasses are crucial for this.
Conclusion – signature plants can be very useful for evoking atmosphere, so long as the vast majority of viewers can read them.
A relatively low-growing combination of plants makes the most of a poor soil, in a place which can get cold winters and is on the drier side of England. It is the kind of planting, like Beth Chatto’s in Essex, which fits plants to habitat. Colorful and rich in textures, it makes the best of its lean look. A dramatic use of waves of a Molinia grass variety is another play with a simple modernist-formal feature.
Conclusion – poor soil and less than perfect conditions can be reflected in planting in a positive way which helps to create a sense of identity.
Bands of Molinia caerulea ‘Poul Petersen’ at Scampston Hall in Yorkshire, northern England, were designed in 1999 but retain their freshness as a design feature, powerfully emphasizing the potential of grasses as material for contemporary formal structure.
Part of the Salvia River in Chicago’s Lurie Garden, where a mix of early summer flowering Salvia cultivars are used to dramatic effect: S. ×sylvestris ‘Mainacht’ (‘May Night’), ‘Blauhügel’ (‘Blue Hill’) and ‘Rügen’, and S. nemorosa ‘Wesuwe’. The grasses are mostly Sporobolus heterolepis.
FROM NEAR TO FAR – COMPLEXITY AND SCALE
Intermingled planting styles offer complexity and diversity. But how easily is this read by the viewer? Is there not a danger that it just looks like a chaotic mush? Much must depend on the plants used in it. There is a clear need for structural plants, as relying on color alone risks the planting dissolving into amorphousness once the flowers die. More fundamentally, though, what does the eye see at different scales? It is important to stress here that there is a difference between random complexity and designed complexity.
On a large scale, there is the phenomenon of seeing the wood not the trees: viewing a mixed planting as a vegetation, as a community, not the individual plants in it – one reads only the patterns. What in fact is a highly complex mixture becomes resolved into a unified whole that is greater than the sum of the parts. Within this whole, individual placing does not matter, and randomization works as well as anything else. If it can be seen to work in the long term, this tendency suggests that the mixed planting style has a great future for use in large spaces. In smaller or more intimate spaces, the very randomness of the mix lets it down. As the scale gets reduced, so the importance of limited key spaces within sight becomes greater. What occupies those spaces is too important to be left to chance. Blending and intermingling varieties is possible, but they need to be much more precisely placed. As far as individual plant placement is concerned, control over exact location becomes more important the smaller the planting. At this level, layering becomes of greater importance than at larger scales. If there are plants at different heights within the planting with varying habits – upright, clump-forming, ground-hugging, sprawling – plenty of scope exists for creating rich visual interest.
The distance from which we view a planting makes all the difference in our perception of its scale. Have you ever seen a wildflower meadow from the air? No. Because at that height the flowers blur into the grass and it becomes a green whole. In the garden, some plants sink into insignificance at certain distances, not just because they are small, but because they lack outstanding color or form. Others can make an impact at a distance, but only if grouped, whereas some stand out as individuals.
Stipa gigantea needs to be positioned right to be fully appreciated, even more than other grasses. Arguably, it is more successful at higher latitudes where side or back lighting illuminates it more effectively – this garden is in western Ireland. The deep blue to the left is Agastache ‘Blue Fortune’.
Sustainability has become a key concept but also a much-abused one, partly because it has become heavily politicized on the one hand and reduced almost to a cliché on the other. It is generally understood as meaning reducing inputs of non-renewable resources and harmful outputs. Like so much else, it is best seen as part of a gradient. Passive sustainability can be understood as not doing actual harm through causing pollution or CO2 emissions and over-exploitation of resources.
Active sustainability can be thought of as to do with not just minimizing harm to the wider environment, but actively managing and improving it through some of the methods discussed in the Introduction: green roofs, rain gardens, biofiltration. These fields are all quite specialist, but can use the kind of diverse herbaceous vegetation highlighted here very effectively. The input of gardeners and designers into such active systems is to provide the aesthetic dimension. Plant selection has fundamentally to serve certain functions, based on a knowledge of plant physiology, best understood by appropriate specialists. However, leaving plant selection entirely with technicians rarely achieves the most aesthetically pleasing results, and gardeners and designers have a role to play in working with plant lists provided by the specialists.
BIODIVERSITY AND THE NEEDS OF NATURE
Whereas once the needs of wildlife were not recognized, contemporary expectations are that planting should support some part of the web of nature. The good news is that providing for biodiversity is not difficult – in fact, many gardeners were doing this long before the word was even invented. To summarize some of the scientific work on the issue, the most important aspects of planting design for animal diversity are a range of habitats, such as is provided by a combination of trees, shrubs, perennials and ground-cover vegetation, and – crucially – connections between habitats. Promoting diverse perennial vegetation which stands over a long season is a good start, with woody plants and tree cover also having an important part to play. The use of regionally native plants may help but is not absolutely vital.
Nature thrives on diversity, and so it should come as no surprise that the intermingled planting approach has enormous potential for supporting biodiversity. It is not that conventional block planting is necessarily deleterious, but the possibilities for improving resources for biodiversity are greatly improved with more diverse intermingled plantings.
Wilderness in the city – this is an area of the High Line in October. A variety of seedheads provides food for birds and small mammals. A high percentage of native species will help support those specialist invertebrates which will only eat specific plants. The brown grass on the right is Chasmanthium latifolium, a relatively shade-tolerant North American species.
SECOND GUESSING THE FUTURE – CLIMATE CHANGE AND DIVERSITY
We live at a time when the impact of possible climate change hangs over us like a threatening thunder cloud. The garden and landscape world has, with agriculture, a part to play not only in reacting to climate change but also in its mitigation.
Climate change is often mistakenly described as ‘global warming’. A two-decade run of mild winters in north-west Europe led to much complacent planting of warmer climate species during this period: there was almost a sense of some gardeners even relishing a new warmer climate and the ability to pick their own olives and pomegranates. At the time of writing this region has experienced a run of cold winters, and climate experts now say that climate change may lead to colder winters here. The gardens of the English Midlands are full of dead Eucalyptus, Cordyline and Phormium. The one certainty about climate change seems to be greater uncertainty – the prospect of more extreme weather. We need resilient plants.
Fortunately, there are a great many resilient plants, and we already garden with quite a few. There is more scope for not only making new introductions from the wild but introducing a wider genepool of the species already in cultivation. Many of the plants relied on are descended from one single introduction, and may be quite unrepresentative of the species as a whole. We could be missing out on forms which are not only distinct in visual terms but able to cope with different or more extreme environmental stresses. Astrantia major is a species common in central Europe; new seed collections and therefore new genetic material for cultivation can be made by driving into a layby in Austria and leaning out of the car window – not surprisingly, there is a considerable range of color and vigor of the species in cultivation. Phlomis russeliana is another perennial which in cultivation shows almost no variation whatever, despite being an extremely useful plant, particularly for plantings requiring very low levels of maintenance. Introducing new genetic material from the wild would require more planning and more effort, and traveling further away from the localities where the plant would most likely be used. It may well come about that up-and-coming growers in Phlomis’s native Turkey will eventually make these collections. We need to create plantings resilient to changing weather patterns by making far more effective use of nature’s bounty of diversity.
There is one further aspect to the importance of genetic diversity among cultivated plants – diversity can increase resilience in plant populations which are dynamic and self-replicating through self-seeding. Currently, professional planting design assumes that the plants used will be permanent. Private gardeners recognize that the seeding of short-lived perennials or biennials can play an important part in the appeal of their plantings. The acceptance of a dynamic element in larger or public plantings implies self-sowing and a natural process of plant replacement. This is particularly likely to be seen as desirable in randomly mixed plantings. A planting where self-seeding is happening involves a reshuffling of genes and so the appearance of seedlings ever so slightly different to their parents. Some of the seedlings will be better able to cope with the extremes of weather than their parents, and so, through being dynamic, the planting will be able to adapt over time in the way that a natural plant community does. In theory! In practice, most elements will be so long-lived that any change will happen on a time scale far too long to be meaningful. However, this process of adaptation over time (which, incidentally, beautifully illustrates Darwin’s theory of evolution) can make a real impact for shorter lived species or those which readily self-seed.
A good example of the potential for Darwinian natural selection to make a meaningful impact on gardens is provided by the South African genus Dierama, a member of the Iris family (Iridaceae) of great beauty, which commonly thrives and enthusiastically self-sows in gardens on north-west Europe’s Atlantic rim. The plants are variably hardy, but naturally grow in dry-winter climates, adding to the complexity of their response to cold weather. A run of cold winters can have a real winnowing effect on a plant population, with survivors flourishing and reproducing, non-survivors (and their genes) making their way to the compost heap. The result within a garden can be a reliably hardy and resilient population of a beautiful and elegant plant.
Much planting design practice to date has relied on genetically identical plants – cultivars. Cultivars are favored by gardeners and designers because of their consistency, yet they have disadvantages. That clones or extensively grown varieties with narrow genepools are susceptible to the spread of disease is well established in agriculture, especially after the USA nearly lost most of its corn crop in 1968. In addition, some cultivars will not self-seed because of a natural tendency for many perennials to ‘out-breed’: they will not self-seed unless there is genetic difference between the prospective parents. Even if they do produce viable seed, the genepool of a population of seedlings from a cultivar will be restricted. A more ‘natural’ varied population will have within it a much wider range of genes, with all this implies for a greater adaptability. Again, Dierama offers a good example, as several species are in cultivation and they crossbreed very easily; the result is a range of genetic diversity from which cold winters can select a strain which will survive long term.
Preparing for climate change should arguably be about selecting plants which survive multiple stresses. A good reference habitat is the steppe of eastern Europe and central Asia with its cold winters and dry summers – analagous to short-grass prairie and sagebrush country. An advantage of many steppe and other drought-tolerant species is attractive silver-gray foliage, such as Artemisia pontica here. The yellow is Euphorbia seguieriana subsp. niciciana. The yellow-green grass foliage is Sesleria autumnalis, the pale grass spikes Melica ciliata, and the very long silvery grass heads are a form of Stipa pulcherrima – this magical effect is unfortunately short-lived. This is early summer.
THINKING THROUGH RESOURCES – SUSTAINABILITY QUESTIONS
Another major issue raised by sustainability is that of resource use – essentially a complex of issues comprising the exploitation of non-renewable resources, including those for energy production, and the generation of CO2 and other pollutants through transport and other energy-consuming activities connected with garden and landscape construction and maintenance. Perennial planting almost by definition looks to the long term, and is therefore less resource hungry than traditional seasonal bedding. Little auditing has been carried out, but it is likely that the continual use of mowing machinery for keeping turf grass short involves greater resource consumption and CO2 output than the maintenance of perennial plantings. The creation of perennial plantings can involve considerable resources, and this is the main area where we all need to look closely at sustainability issues. Consideration of these issues needs to be carried out objectively and on the basis of evidence; sustainability and other environmental issues are notoriously political, and much decision-making by both private individuals and institutions is carried out in an atmosphere clouded by emotive and ideological considerations – the British debate over the use of peat in potting composts is a good example of this.
The horticulture industry used to be notably insensitive to resource use. Plastic pots and other containers that cannot be recycled, energy for heating and lighting propagation facilities, and compost all gobble up resources and require physical materials and energy for their production and crucially their transport. Over recent years great strides have been made: reusable or recyclable containers, the widespread use of composted green waste for potting and soil improvement and of slow- release fertilizers which reduce the wastage of nutrients, and much more. However, there is one tendency which still needs questioning – the size of plants in new projects. It is accepted that small plants usually establish better and more quickly than large ones. Yet, so many new planting schemes, both private and public, involve the purchase of container-grown plants far larger than would have been traditionally used. Moreover, these plants often travel long distances from nursery to site. So, two issues have come together which massively increase the embodied energy of many commercially grown plants. Every perennial in a two-liter pot as opposed to a half-liter one weighs four times as much and takes up about four times the space in a delivery truck; delivery from a nursery 400 kilometers away uses four times as much fuel as from one 100 kilometers away. Do the math!
The case for using small plants is easily made for perennials, which tend to grow quickly, but is less easily made for woody plants. Many design professionals are under pressure from clients for quick results (those spending public money are often worse than private), and it can be difficult to resist. What can clinch the argument is pointing out that small woody plants often catch up with larger ones in a few years, such is their superior ability to adapt and make the best of new circumstances. It is also worth remembering that large (and therefore expensive) plants are high risk – they are more prone to wind damage and drying out, and so large initial investments are more likely to be lost than small ones. Small plants are not only more sustainable, but a safer investment too!
On the High Line, regionally native plants make an impact. Fine, blue-gray grass at the centre Schizachyrium scoparium ‘The Blues’ with Bouteloua curtipendula (the grass with fine, one-sided seedheads), yellow Rudbeckia subtomentosa and in the background Vernonia noveboracensis. All of these are now well established in cultivation.
The days of automatically cutting down dead perennial growth in the autumn are long gone. Most gardeners and those involved in plant management are now familiar with the idea that seedheads feed birds and may harbor a variety of invertebrates too. The idea that the city can be a habitat is widely accepted in the industrialized world. It is also worth pointing out the value of misty weather adding a sense of drama to combinations of tall perennials, such as this Angelica gigas on the Westerkade in Rotterdam.
Early autumn at Hummelo with the lush perennials and grasses which create so much of the distinctive character of this time of year. Grass Molinia caerulea ‘Transparent’ with pink Eupatorium maculatum ‘Riesenschirm’, the tiny red heads of Sanguisorba ‘Bury Court’, white Persicaria amplexicaulis ‘Alba’ and yellow Solidago ×luteus ‘Lemore’.
Regionally native plants bring nature and a hint of the wilderness to the High Line in early autumn. Rhus typhina is already changing color, as the flower-heads of Eupatorium hyssopifolium repeat down the line. Aster oblongifolius ‘Raydon’s Favorite’ is just visible – an example of an increasing trend in naming cultivars of native plants.
Plants in designed landscapes may even play a role in conservation. The graphic qualities of the royal fern (Osmunda regalis) are used here in a private garden (Dyffryn Fernant, Pembrokeshire, Wales), creating visual weight amongst a mass of finer foliage. This species is now very rare in the wild but extremely long-lived, making it a good landscape plant.
NATIVES AND EXOTICS – THE DEBATE CONTINUES
The long-standing debate over the role of native and exotic (introduced) species continues, with an unfortunate tendency toward adopting entrenched positions in some countries (such as the USA) or arousing little interest in others (Japan). The key issue is the role of plants in gardens and designed landscapes to contribute to biodiversity by supporting food webs of insects, birds and other wild animals. It is worth noting the positions adopted by leading practitioners working in planting design. There does seem to be a consensus that using only native species is entirely appropriate in certain environments – chiefly rural ones or where the conservation of local and indigenous biodiversity is a priority. In many other situations, planting in the past would have used mostly or entirely non-native species, but now involves a larger proportion of natives.
The strictly nativist lobby, which believes in the exclusive use of regional natives, is not one which has arisen from within the garden and landscape communities, but rather has been imported from outside, from the world of environmentalist politics, where ecology is a word which can often weave dangerously between the evidence-based and scientific and the emotive and ideological. Unfortunately, the native plant lobby has on occasion acquired sufficient political support in some communities that the use of native plants has been mandated for landscaping projects, compromising their visual effectiveness and therefore the public support they receive.
Piet Oudolf’s work at the Lurie Garden in Chicago and the New York High Line provides an example of synthesis which many in the profession would agree with. He chooses plants because they perform a function and meet certain visual criteria. In these two projects over half the plants used are natives of their region. One of the criteria for both commissions was that the planting should reflect something of the regional natural environment: in the case of the High Line, this being the plant community which had established on the elevated rail line prior to restoration. A large proportion of natives was therefore essential. Crucially, though, the plants selected highlight just how good in design terms many of the plants in these regional floras are – a great number of species with garden and landscape potential have been largely ignored up until now. This is perhaps the most crucial point here – that prior to the current wave of interest in native plants, the nursery industry produced and sold what was beginning to look like a global flora of easy to use, easy to propagate plants. In the case of plants used by the landscape industry, they may have been different from one climate to another, but the effect was the same – too often both architecture and planting could be anywhere. The use of a proportion of locally native plants can do much to add a distinct signature to projects.
The native/exotic debate is complex, and here we will consider a range of points, some of which are more relevant to some localities than others.
A meadow of the US native grass Sporobolus heterolepis in a garden on Nantucket Island, Massachusetts, includes Echinacea purpurea, a species which has become something of a poster boy for promoting native plants. It is important that planting schemes for biodiversity combine species which really support wildlife effectively as well as those which simply look good and tick the ‘native’ box.
