Chapter 2

Rootstocks

More than 99 per cent of fruit trees are grown on a rootstock. In order to choose a fruit tree for your orchard, you will need to know a little about rootstocks, particularly because the rootstock has a large influence on the eventual size of your tree. For example, a Cox’s Orange Pippin grown on a vigorous M25 rootstock will grow into a large tree up to 10m (331) tall, whereas the same variety grown on a dwarfing M27 rootstock might only grow to about 1.5m (5') tall.

For nearly every fruit tree you plant, there will be a choice of rootstocks. While some rootstocks are suitable for certain soils and some confer resistance to certain diseases, by far the most important characteristic of a rootstock is the effect it has on the eventual size of the tree.

This allows you a lot of flexibility when planning your orchard. Choosing the correct rootstock will save you a lot of heartache later on. It is no use trying to prune a fruit tree hard because it is getting too big for your garden; you will only succeed in creating a tree with lots of upright vegetative growth that will gradually lose its fruiting potential.

Why use a rootstock?

If you grow an apple tree from a pip, you will not end up with the same variety of tree you started with, because apple trees are cross-pollinated. This means that the flower of an apple needs pollen from another apple variety to successfully produce a fruit. The pips of that apple will share the characteristics of both varieties. So if you plant the pips from a Cox’s Orange Pippin, you will end up with a fruit that shares the characteristics of a Cox and the variety that pollinated it.

Some apple varieties that are well known today originated from seedlings. The Bramley’s Seedling cooking apple originated from a chance seedling planted in 1809 (see box overleaf). Very few apples will grow successfully from cuttings, so to reproduce a known variety of apple, grafting is necessary.

The process of grafting

Grafting is the process of fixing a cutting, known as graftwood or scion wood, to a root-stock in such a way that the living tissue in both will fuse together to make a strong bond. This is achieved by cutting a shape in the top of the rootstock that is mirrored by a corresponding but inverted shape in the graftwood, so that they can come together without any gaps. The two parts are held firmly together and then wrapped tightly with a biodegradable tape that will perish once the union is strong enough. Once the bond is formed and the tree is growing, the graft or union will be recognisable as a distinct knobbly shape on the lower trunk.

Left: A large apple tree in a traditional orchard. The size of a tree is largely determined by the rootstock.

THE STORY OF BRAMLEY’S SEEDLING

The story of our quintessential English cooking apple started in around 1809 when a young woman called Mary Ann Brailsford planted some apple pips. One of the resulting trees turned out to be fine green cooking apple that cooked to a sharp purée.

In around 1857, or so the story goes, a local nurseryman by the name of Henry Merry-weather came across the local vicar carrying a basket of these apples. Recognising a good apple, he asked the vicar where they came from. The vicar took him to Mary’s tree and the rest is history.

Merryweather took graftwood from the tree and started selling the young trees, naming them after Matthew Bramley, who was now living in the house where Mary had lived. In the late nineteenth century the Bramley apple achieved fame and recognition at the Royal Horticultural Society shows. By the 1920s, large acreages of Bramley trees were being planted as commercial orchards.

Amazingly, the Bramley has now eclipsed all other British cooking apples. It keeps well, has a good flavour and cooks to a pulp, which English cooks prefer.

Bramley’s Seedling.

The bulge in the trunk is the union between the rootstock and the scion. This should be well above ground level after planting.

It is important to recognise this shape, to ensure that it is above the soil when the tree is planted (see Chapter 6).

Some orchard groups run courses that teach you to graft your own fruit trees. (You can find your local group via the website www.orchardnetwork.org.uk.) This is an excellent and satisfying way to reproduce an old favourite tree, if you don’t know its variety. Grafting is usually carried out in late winter. There is also another method of producing fruit trees, known as ‘budding’, often used by commercial nurseries: this where just one bud is inserted into the rootstock, usually in the late summer. Amazingly, a whole apple tree will develop from just that one bud.

Characteristics of different rootstocks

In the early days of grafting, tree nurseries did not exist, so grafting would have been largely the preserve of farmers and smallholders wishing to propagate successful trees. They did not have access to specially prepared rootstocks as we do today, so they would use whichever trees were close to hand. The rootstock also had to be compatible with the graftwood. For example, pear graftwood can be grafted on to a quince or a wild pear rootstock, but not on to a cherry or plum. Apples were usually grafted on to crab apples or apple seedlings.

More recently, with the commercialisation of the fruit industry, much research has been carried out into rootstocks, particularly with apples. This has resulted in a range of root-stocks, named with codes such as M25 or MM106 – which can be confusing to the novice fruit grower.

By far the most important characteristic of these rootstocks is their effect on the eventual size of the fruit tree, but their imprint will also affect the tree in other, more subtle, ways – for example, in resistance to specific pests and diseases and suitability for different soils.

Dwarfing rootstocks

In the past, most fruit trees were of a large size, but modern developments in rootstocks have enabled the cultivation of dwarfing or semi-dwarfing trees. These smaller trees are more suited to both the commercial grower and the amateur because they can be sprayed, pruned and harvested from the ground rather than using the long ladders of days gone by.

As gardens have become smaller, dwarfing trees have become increasingly convenient. Growing trees on dwarfing rootstocks allows you to grow many more varieties in the same area of garden. For example, instead of growing two varieties of a large apple tree, you could plant a number of small trees that would give you both cookers and dessert varieties, early and late, as well as more room for other fruits. Trees grown on more dwarfing rootstocks tend to bear fruit sooner in their lives than trees grown on more vigorous rootstocks.

There are, however, disadvantages of dwarfing rootstocks. Generally, the smaller the tree, the more nurturing it requires. Some of the most dwarfing apple rootstocks, such as M27 or M9, will struggle on poor or chalky soils. More attention will need to be paid to feeding the tree as well as to keeping the area around the trunk free from grass and weeds. Obviously these trees produce much smaller crops than large trees, which might seem like a disadvantage, but then do you need half a tonne of an early apple that will keep for just three weeks or so?

Vigorous rootstocks

A vigorous rootstock will produce a large tree, sometimes over 10m (33') tall and wide. While there are obvious difficulties with managing trees of this size, if you do have the space for an orchard of such trees, you will be rewarded with not only large quantities of fruit but also the beautiful sight of a traditional orchard in the landscape. These orchards, particularly at blossom time and at harvest time, are a sight to behold; by planting such an orchard you are doing much to enhance the landscape in a way that has been done for centuries.

Such orchards offer the potential for very large crops, much larger than you will be able to eat, even if you have a large family. This is where juicing and cider-making come into play. Because much of a large tree is out of reach, most of your harvest will be windfalls or shaken apples. These are likely to be bruised, so they will not keep long; however, juicing them, either for cider or juice, is a way of using and potentially preserving them in large quantities. Fresh juice can be preserved by pasteurising or freezing.

Another advantage of trees grown on vigorous rootstocks is that they can be trained so that grazing animals can keep the grass under control – which can otherwise be a demanding task on an orchard scale. Although formative pruning is needed, such trees need little looking after once established. They can live for over 100 years, compared with around 20 years for some of the more dwarfing rootstocks.

The main disadvantages of vigorous root-stocks are the difficulties in reaching the trees and the long time before cropping begins. It is not uncommon to wait eight years before a standard tree bears substantial crops.

A traditional apple orchard reclining gently in the landscape.

Semi-dwarfing rootstocks

For many people, semi-dwarfing rootstocks are a suitable compromise between dwarfing and vigorous rootstocks. They are reasonably quick to start fruiting, don’t take up too much space and are manageable from the ground – albeit with long-handled tools as they grow taller. Examples of such root-stocks are MM106 for apples, Quince A or C for pears, and St Julien A for plums.

Rootstocks for different fruits

Choosing the correct rootstock is as important as choosing the right variety. The information on the following pages will help you to make this choice with confidence.

Apple rootstocks

The first half of the twentieth century saw much research into apple rootstocks, particularly in England. Many of the rootstocks now commonly in use were developed at this time, mostly at government research stations, such as those at Merton and East Mailing. The names of these research stations gave rise to the prefixes M (East Mailing) and MM (Malling-Merton) that are found preceding some of the most common apple rootstocks.

PLANTING DISTANCES

The rootstock largely determines the spread of the tree, although this can vary slightly – up to a metre – depending on the vigour of the cultivar. The spread indicates how far apart trees should be planted. So, a tree with a spread of 2m (6'6") could be planted 2.5m (8') from other trees, allowing for room to walk around the tree when harvesting or pruning. Planting trees far enough apart, so that they have gaps between them when mature, decreases their susceptibility to fungal disease.

The most useful apple rootstocks are listed here, starting with the most dwarfing (see Chapter 8, pages 109-112, for descriptions of tree forms).

M27 An extremely dwarfing rootstock. Needs permanent staking. Requires fertile soil and lack of competition from weeds or grass. Fruits early in its life. Will not tolerate wet soils. Suitable for dwarf-trained trees. Mature height 1.2-1.7m (4'-5'6"); spread approximately 1.5m (5').

M9 A very dwarfing rootstock. Needs permanent staking. Requires fertile soil and lack of competition from weeds or grass. Fruits early in its life. Will tolerate wet soils but not drought. Can be prone to canker in wet soils. Suitable for training as a bush or spindlebush; also small trained trees such as stepovers and cordons, and pot-grown trees. Height 1.7-2.5m (5'6"-8'); spread 2.5m (8').

M26 A dwarfing rootstock. Needs permanent staking. Will not tolerate wet and heavy soils. Fruits early in its life. Liable to produce burr knots, which can be colonised by pests such as woolly aphids. Susceptible to crown rot and fireblight. Suitable for most forms of training, including cordon and espalier, as well as pot-grown trees. Height 2.5-3m (8-10'); spread 3.5m (11'6").

Diagram 4 The size of tree produced by different apple rootstocks.

MM106 A semi-dwarfing rootstock. Needs staking early in its life. Suitable for most soil conditions. Susceptible to crown rot. Resistant to woolly aphids and fireblight. Suitable for training as a bush, spindlebush or large wall-trained tree. Height 4-5m (13-16'); spread 4m (13').

MM111 A semi-vigorous rootstock, not often found. Needs staking only early in its life on windy sites. Prone to burr knots but resistant to woolly aphids. Suitable for training as a half standard or standard. Suitable only for orchards and large gardens. Height 5-8m (16-26'); spread 7m (23').

M25 A vigorous rootstock. Needs staking early in its life on windy sites. Susceptible to woolly aphids. Suitable for training as a half standard or standard. Suitable only for orchards and large gardens. Height 6-10m (20-33'); spread 7-10m+ (2-33'+).

Pear rootstocks

Traditionally grown on wild pear rootstocks, most pears these days are grafted on to quince rootstocks. The most common pear rootstocks are as follows.

Quince C A moderately vigorous rootstock producing a tree 3.5- 4 metres (11'6"-13') tall that will start bearing fruit when 4-5 years old. Spread 3-3.5m (10'-11'6"). Prefers fertile soil conditions. Intolerant of dry and chalky soils. Suitable for all forms of tree except standards.

Quince A A medium-vigour rootstock producing a tree of 4-4.5m (13'-14'6") tall that will start bearing fruit when 4 to 6 years old. Spread 3.5-4m (11'6"-13'). Prefers fertile soil conditions. Intolerant of dry and chalky soils. Suitable for all forms of tree except standards.

Pyrodwarf A new medium-vigour rootstock originating from Germany. Similar in size to Quince A rootstock, but more tolerant of less favourable soil conditions. Fruits earlier in its life than quince rootstocks.

Wild pear (Pyrus communis) A very vigorous rootstock, producing trees 10-15m (33-49') tall. Some resistance to honey fungus. The spread of trees on pear rootstock can vary considerably, depending on the variety: if you are unsure, allow at least 10m (33') between trees.

Plum rootstocks

In the past, plums have often been grown on their own roots (i.e. without a rootstock) and propagated by the lifting of suckers. The use of rootstocks has now become the norm, with a choice of several rootstocks giving a range of tree size.

Pixy The most dwarfing rootstock, resulting in a tree 2.5-3.5m (8'-11'6") tall and 3m (10') across. It is suitable for bush and pyramid forms and for fan-training. Because of its size and disease resistance, Pixy is increasing in popularity. It has some resistance to silver-leaf and bacterial canker, two of the most common diseases on plum trees. It prefers a fertile soil and doesn’t tolerate drought well.

St Julien A A semi-vigorous rootstock producing trees with a mature height of around 3.5-4.5m (11'6"-14'6"); spread 4m (13'). It has been the most common plum rootstock for a long time and is tolerant of a range of conditions. Suitable for bush and half standard forms or training as a large fan. Its main drawback is its susceptibility to bacterial canker. It has some resistance to honey fungus.

Brompton A vigorous rootstock that is now declining in popularity because of its large size. It is really suitable only for training as a standard or half standard, giving trees of a height and spread of 5-6m (16-20'). It is suitable for most soil conditions.

Cherry rootstocks

Although related to plums, cherries use completely different rootstocks. In the past, cherries were grafted on to wild cherry seedlings, giving rise to huge trees up to 15m (49') tall, harvested from very long ladders. The introduction of dwarfing rootstocks was particularly important for cherries, because netting is often needed to prevent birds from stripping the fruit from the tree.

Most cherry trees for growing in garden situations are now grown on Gisela 5 rootstocks, although Gisela 6 might also be available from some nurseries. This is a slightly more vigorous rootstock than Gisela 5, more suited to weaker-growing cultivars, such as Lapins. Trees grown on Colt and F12/1 root-stocks are much larger, making them harder to net, spray or harvest.

Gisela 5 A comparatively new rootstock that is replacing Colt (see above right) due to its smaller size (40 per cent smaller) and precociousness. Mature trees are only 2.5-3m (8-10') tall and 3m (10') across, so fairly easy to net.

Colt A semi-dwarfing rootstock, with mature trees 3.5-4.5m (11'6"-14'6") tall and 4.5m (14'6") across. Trees on a Colt rootstock will tolerate a wide range of soil conditions.

F12/1 A vigorous rootstock that can still sometimes be found, giving rise to trees over 6m (20') tall.

Peach, nectarine and apricot rootstocks

Peaches, nectarines and apricots are grafted on to the same rootstocks as plums, to which they are closely related, with one or two important additions.

Montclaire A new, highly productive root-stock for peaches and nectarines that results in a slightly smaller tree than when St Julien A is used. It makes trees less susceptible to frost damage, which could make peaches an easier crop to grow in Britain. Montclaire rootstock produces trees around 3.5-4m (11'6"-13')tall.

Torinel A recently introduced rootstock for apricots, which is becoming more popular. It is slightly smaller than St Julien A, suitable for a wide range of soil conditions and highly productive.

Figs

Figs are grown on their own roots. It is good practice to plant figs where their roots can be restricted, by walls or paving for example, in order to control their growth and promote fruiting.

Mulberries

Mulberries can be propagated by taking cuttings and they can also be grafted. You will not find any choice of rootstock. Growing trees on a rootstock brings them into fruiting earlier in their life. When mulberries are grafted on to a rootstock, it is usually Mows alba, the white mulberry.

Quince rootstocks

Quince trees are grown on quince or wild pear rootstocks. Quince rootstocks will produce a small tree, around 3.5-5.5m (11'6"-18') tall and around 5m (16') wide. Hawthorn rootstocks produce slightly bigger trees, but with less stable roots. Although rarely found nowadays, medlars can also be grafted on to wild pear rootstocks, leading to very large trees about 10m (33') in height and spread. All three will tolerate relatively poor soil conditions. See ‘Pear rootstocks’, page 33, for details of these.

Medlar rootstocks

Medlar trees can be grown on hawthorn (Crataegus monogyna), quince or wild pear rootstocks. Hawthorn and quince will produce semi-dwarfing trees, whereas wild pear will produce a large tree. All three will tolerate relatively poor soil conditions. See ‘Pear rootstocks’, page 33, for details of quince and wild pear rootstocks.

Medlars can be grown on hawthorn, quince or wild pear rootstocks.

QUICK GUIDE TO ROOTSTOCKS

The variety of fruit tree that you want to grow will be grafted on to a rootstock. The following points will help you choose the correct rootstock.