The yellow-flowered form of the multi-headed Aloe arborescens provides the visual background for a variety of densely cultivated indigenous plants.
Although it is hard to generalize about the ‘ideal’ conditions and habitats in which to grow aloes, there are some guidelines that can be widely applied.
Factors associated with rainfall, such as seasonality, amount and type, play an important role in, and affect the distribution ranges of, species of Aloe. For example, species that occur in the winter-rainfall region of southern Africa generally do not grow well in open beds in summer-rainfall regions, unless the beds are protected from unseasonal rainfall. The opposite is true of summer-rainfall species. Bear in mind that Aloe species from summer-dry areas need a very well-drained soil mixture, even if they are grown in other winter-rainfall areas, especially if the annual precipitation of their new home considerably exceeds the little received in their natural habitat.
Contrary to popular belief, aloes appreciate generous watering during the growing season, particularly during warm periods. Even during the resting phase, plants should be given a light watering to prevent unsightly die-back of the leaf tips. However, resist the temptation to drench them regularly at this time, as over-watering will almost certainly lead to root and/or stem rot. Watering is directly related to the soil mixture in which aloes are grown; plants grown in a friable, well-drained medium will demand more regular watering than those kept in a more clayey one.
As a rule of thumb in the southern hemiphere, aloes from summer-rainfall regions should be watered during months that contain an ‘r’ in their name. Watering should therefore be curtailed in May, June, July and August. In contrast, winter starts much earlier for winter-rainfall species and they can be given increased levels of irrigation from as early as March through to September.
Do not leave potted aloes standing in water for extended periods of time, as this can cause their roots to rot. For established aloes, regardless of whether the plants are grown in the open or in containers, overhead watering is best, as it flushes accumulated dust and soil particles from their leaves. However, in areas where the salt content of irrigation water is high, overhead watering will leave unsightly white crusts on the leaves and drip irrigation may be the best alternative.
Remember that large-growing plants are better able to store water than smaller ones. It is therefore preferable to continue to water small plants occasionally, even during the resting phase. All aloes will also benefit from an occasional misting, if for no other reason than to keep their leaves dust free. Misting also tends to raise the air humidity, which is something that aloes favour.
The robust leaves and dense, orange inflorescences of Aloe thraskii make for a striking feature in a coastal garden.
Generally, aloes grow better in atmospheres that have reasonable levels of humidity (the amount of moisture in the air). This applies particularly to thin- or flat-leaved species such as the grass aloes. During the non-rainy winter season, the air over much of the southern African interior is extremely dry. Coastal species that are transplanted to the interior tend to suffer, unless some additional overhead irrigation is supplied. In contrast, species from the interior transplanted to the coast generally do better in cultivation, for the coastal air is naturally much more humid.
Aloe lineata var. lineata, a shrubby species originating from the Eastern Cape, works well in coastal gardens. The plants can grow about as tall as a grown man.
Temperature plays an important role in determining the geographical distribution ranges of plants, as well as determining which aloes can be used in gardens, and where. Most aloes flourish at high temperatures. However, in much of the inland distribution range of aloes, frost is common and this impacts adversely on coastal species transplanted to the interior.
Most aloes enter a vegetative resting, or dormant, phase during the cold winter months. (This applies much less to the few aloes indigenous to the Mediterranean region of the southwestern Cape where, among others, Aloe plicatilis, A. haemanthifolia, A. brevifolia and A. commixta occur naturally.) However, regardless of the area from which the plants originate, almost all aloes can tolerate some light frost, especially if the soil in which they grow is relatively dry.
The majority of aloes flower in winter, making the flowers and inflorescences particularly vulnerable in areas that are subjected to very cold snaps, when they can suffer severe frost damage. Although aloe leaves tend to die back from the tips under these conditions, they usually recover very quickly when temperatures start to increase in spring. A general gardening rule is that roots are typically less cold-hardy than stems and leaves, and that, in frost-prone areas, aloes tend to be more tolerant of low temperatures if the soil is kept dry – they definitely don’t like very cold, wet soil.
Generally speaking, temperatures below about -5 to -7°C will severely damage or kill most aloes. The few species that will survive beyond these temperatures include Aloe davyana, A. striatula, A. polyphylla and A. transvaalensis, whose natural habitats straddle the climatically severe Highveld or adjacent high-altitude areas. These species can survive low night temperatures for extended periods, while often the temperature the following day will be up to 20°C higher, with no apparent ill effect to the plants. Significantly, the majority of these species flower in summer (or at least not in mid-winter).
If you want to garden with aloes in very cold areas, make sure you either cultivate species naturally confined to such areas, or select forms of more widespread species that originate from the coldest parts of their range.
In species whose natural distribution covers a wide geographic range, several genetic forms best adapted to local environmental conditions may develop through natural selection over long periods of time. If some parts of a particular species’ range are colder in winter than elsewhere in its range, plants originating from the colder parts are likely to be more cold-tolerant.
Known as ecotypes, these local genetic forms are often not morphologically distinct from other members of a species, hence they are usually not formally recognized by scientific names.
The list below is simply a guideline as to how well individual species can tolerate varying degrees of frost. The plants were selected based on cultivation on the Highveld.
Frost tender (to 0°C) |
Aloe africana |
Aloe brevifolia |
Aloe plicatilis |
Aloe thraskii |
Light frost (to -4°C) |
Aloe aculeata |
Aloe barberae |
Aloe ciliaris |
Aloe comptonii |
Aloe cryptopoda |
Aloe excelsa |
Aloe dichotoma |
Aloe haemanthifolia |
Aloe pillansii |
Aloe ramosissima |
Aloe speciosa |
Mild frost (to -7°C) |
Aloe chabaudii |
Aloe ciliaris |
Aloe cooperi |
Aloe ferox |
Aloe fosteri |
Aloe globuligemma |
Aloe maculata |
Aloe marlothii |
Aloe microstigma |
Aloe petricola |
Aloe pretoriensis |
Aloe rupestris |
Aloe spicata |
Aloe striata |
Aloe thompsoniae |
Aloe vanbalenii |
Severe frost (lower than -7°C) |
Aloe arborescens |
Aloe aristata |
Aloe boylei |
Aloe davyana |
Aloe ecklonis |
Aloe grandidentata |
Aloe kraussii |
Aloe lutescens (some forms) |
Aloe mutabilis (some forms) |
Aloe parvibracteata |
Aloe polyphylla |
Aloe reitzii |
Aloe striatula |
Aloe tenuior |
Aloe transvaalensis |
Aloe verecunda |
Aloe camperi, from East Africa, does well in full sun and partial shade, as here in the Desert Garden, Arizona; it flowers from spring to early summer.
Almost without exception all species of Aloe need ample, bright light, especially as mature plants. However, this does not necessarily mean exposure to the often harsh rays of direct sunlight. Many species, certainly as juvenile plants when their leaves are soft and their roots poorly developed, prefer shady conditions, with filtered – but still bright – sunlight. In their natural habitats this type of shading is provided by nurse plants, such as grasses, small karoo bushes or open-canopy trees. Even leaf litter can fulfil this role, particularly for seedlings.
The leaf tips of some species will die back regardless of the intensity of light to which they are subjected. The summer-rainfall maculate, or spotted, aloes are a good example of this phenomenon. However, their leaf die-back usually results from a combination of factors: low water resources during the resting phase; exposure to extreme temperatures; and high light intensity, which can occur when the loss of shading canopies in winter-deciduous trees suddenly allows considerably more light to reach previously shaded aloes.
If you keep your plants under the protection of glass in the resting phase, or during protracted cold, wet periods, you should continue to protect them from direct sunlight (and even rain) for the first few weeks once they are ready to be re-introduced to sunny positions – otherwise they are sure to get scorched.
Plants usually indicate clearly when they receive too much insolation (exposure to the sun), as their leaves turn a darker green, and ultimately a reddish brown. Although this may look attractive for a short time, it is a sign that the leaves are under stress. If this happens to plants in containers, they should be moved under cover, or to where they will receive filtered sunlight only.
A few species actually thrive in deep shade as adults, notably Aloe suffulta. Others, such as A. davyana, are able to cope with either shade or open, sunny positions.
Aloe pictifolia, a small cliff-dweller from the Eastern Cape, thrives in a dry wall rockery. As a rule of thumb, aloes love sun.
Aloes are generally not fussy about the soil in which they are grown. The grass aloes are the exceptions: they tend to prefer an airy, very friable mixture with reasonable amounts of decomposed organic material (coarse compost) added to the soil. A very important aspect of soil type is its ability to drain well, while still retaining some water. Aloes cannot tolerate wet feet (i.e. soil with poor drainage). There are exceptions, however: in the Drakensberg mountains of the eastern Free State, Aloe maculata has been observed growing in very muddy soil that is virtually water-logged for the entire summer rainy season, with no apparent ill effects to the plants.
In open garden beds it can be difficult to ensure adequate drainage at all times, especially if you are gardening in clayey soils. Under such conditions, a reasonable quantity of sharp sand should be added to the hole prepared for the plants. Before planting a new aloe, the soil should be dug out of the hole and then mixed with copious amounts of sand and, ideally, some compost.