How to Grow and Care for Aloes

Introduction

Long appreciated for their medicinal properties, aloes have been cultivated by humans for thousands of years. These succulent natives of Africa and Arabia (about 500 species in total, plus a great number of hybrids) are practical in dry landscapes and produce colorful, tubular flowers which attract sunbirds (in Africa or Arabia) or hummingbirds (in the Americas). They vary in size from dwarves to giant trees and are generally well behaved container plants. Aloes usually flower once a year or more once they reach maturity.

Care

Most aloes are easy plants given a bright, warm location and water in moderation. Aloes require bright light, and most can take full sun in mild climates. Indoor aloes do best when placed right by an unobstructed sunny window. They prefer good drainage, especially in containers, and regular water when the soil is going dry, but not sooner. Landscape aloes are quite drought tolerant when established but will respond favorably to occasional water. Aloes from dry climates may be sensitive to excess moisture and prone to rot.

Aloes and their close relatives are uniquely susceptible to the aloe mite, a contagious microscopic villain which lives inside the plant and announces its presence in the form of aloe cancer, a chronic and persistent disease. The distorted growth presents various ways, but it looks irregular and "wrong" and is often bubbly at the surface, with orange or yellow highlights. The best treatment of aloe mite is removal of the affected area by careful surgery, potentially including decapitation of affected stems. Consider removing the entire plant. Dispose of mite infested cuttings or plants very carefully, and sterilize instruments after use.

Zero tolerance is the best policy where aloe mites are locally present. Most ordinary pesticides (like the systemic insecticide imidacloprid) do not knock down aloe mites, which are closer genetically to spiders and spider mites than insects. Specialized miticides are available but they tend to be really expensive and require careful use. Chemical agents are not typically going to solve your aloe mite problem on their own, without some careful surgery first.

Some aloes are more susceptible to the aloe mite than others. By far the most common host in cultivation may be Aloe arborescens. Mites tend to show up most often on inflorescences, which give them a great platform for dispersal. Remove affected inflorescences at first sight and monitor the stem afterwards.

Types

Aloes can be divided into groups based on certain features.

The Lomatophyllum group from Indian Ocean islands can be distinguished by a fleshy berry-like fruit, which differs from the usual dry, dehiscent (popping or splitting open) aloe fruit.

The grass aloes have thin, linear leaves and often bulbous bases. They are the least succulent, toothy, or substantial.

The maculate aloes have spotted leaves, relatively short stems, and flowers that are bulbous at the base. They can be particularly difficult to identify, even for experts.

Stemless aloes, a large group, may be solitary or grow in clumps. They are well represented in cultivation. One small stemless aloe (aristata) was recently moved to its own monotypic genus, Aristaloe.

The aloes which grow a stem include sprawling aloes, which tend to grow sideways, and shrubby aloes, which tend to form large, branching groups. The genus Aloiampelos was recently created for 7 related scrambling aloes, including the relatively common ciliaris and striatula.

Two aloes (plicatilis and haemanthifolia) make rounded, distichous leaves in a fan shape, and these were recently separated into the revived genus Kumara.

Three spotted aloes from Namibia have distinctive leaves with a V shape in crossection, and these were recently separated into the new genus Gonialoe.

Finally, tree aloes may grow up to 60 feet tall (the giant is A. barberae). They may be solitary and unbranched (the single-stemmed tree aloes) or branch, either at the base or at the crown. The tree aloes tend to make especially dramatic flowers. The genus Aloidendron was recently created for 6 related tree aloes, mostly on the large side.

Medicine

The “true” medicinal aloe from ancient times is Aloe vera, a yellow-flowered Arabian aloe which only exists in cultivation, and can only be grown true from offsets. This plant was formerly known as Aloe barbadensis.

It is generally unspotted, clumps freely, and reaches a larger size than the other common medicinal aloe in cultivation, Aloe officinalis (also known as Aloe vera chinensis), which can usually be distinguished by orange or coral flowers. Aloe vera gel is used for the topical relief of skin ailments, while Aloe officinalis is said to have benefits when consumed. In addition, Aloe ferox juice extract is promoted for various uses including as a laxative. Do not consume any aloe you cannot definitively identify as medicinal, which usually requires seeing the flowers. This is a diverse genus of many non-medicinal plants and even a few poisonous ones.

Propagation

The aloes which branch or offset are generally easy to start from rooted cuttings or offsets. Some can only be grown from seed. Aloe seed is usually relatively large and quick to get started. Hybrids (including many of the named hybrids in cultivation) will not generally grow true from seed, and most aloes require two flowering individuals to be pollinated (by birds, bees, or humans) and produce seed.

Open pollination in the aloe garden gives rise to all sorts of strange and interesting hybrids. Most species are quite promiscuous; a few may self-pollinate. Seed which is not produced carefully, excluding pollinators, is likely to be less than pure. Wait until the capsule dries up and breaks open to harvest mature seed (except with Lomatophyllum, which makes an indehiscent berry).

indehiscent: In botany, not popping or splitting open spontaneously when mature, as a capsule or an anther.

Relatives

Aloe is closely related to Haworthia (white flowers) and Gasteria (pinkish flowers with a characteristic swollen shape), two mostly South African genera which generally enjoy less direct sun, as well as Astroloba, Chortolirion, and Poellnitzia (these three much less common in cultivation). Aloes may generate intergeneric hybrids with these other plants, and the hybrids may be fertile.

A recent reorganization of the aloes resulted in the splitting of a few species into the genera Kumara, Aloidendron, Aristaloe, Aloiampelos, and Gonialoe (details above), plus a few species absorbed from Chortolirion. At the same time Haworthia was split into three genera with the addition of Haworthiopsis and Tulista.

Recommended resources

Carter, Lavranos, Newton, Walker: Aloes: The Definitive Guide (2011) Brian Kemble's hardy aloes (list) Castillon & Castillon: The Aloe of Madagascar (2010)
McCoy: The Aloes of Arabia (2019)

Some popular Aloes photos:
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