Aloe

The genus best known for medicinal purposes also produces attractive ornamentals, says Miranda Kimberley.

Aloe arborescens - image: Trewidden Nursery
Aloe arborescens - image: Trewidden Nursery

Originating from Africa, the Arabian peninsula and the Indian Ocean Islands, Aloe are succulent plants. There are more than 550 species, which are very diverse in form, varying from trees taller than 70m to small rosettes just 30cm across. The best-known is A. vera, which is grown commercially to produce gel for medicinal and cosmetic purposes, as is A. ferox. Both also make valuable ornamental plants.

While similar in appearance to Agave, they are in fact in a different family - Asphodelaceae - with close relatives Gasteria, Haworthia and Kniphofia. Aloe are either stemless, with a rosette growing directly at ground level, or produce a branched or unbranched stem from which its succulent leaves are borne. These leaves are usually large, thick and fleshy and vary in colour from glaucous to bright green. Sometimes they are striped or mottled, as in the case of the fabulously named partridge-breasted Aloe. They often have spiny margins and finish in a sharp point.

The tubular flowers are borne on densely-clustered, simple or branched leafless stems, and are red, yellow or orange in colour. Older specimens may flower in the UK, but not all species will receive enough heat and light to do so.

The genus is classified as frost-tender, so Aloe are generally grown as houseplants in the UK, but can be put outside in frost-free months. However, certain species, including A. striatula, A. ferox, A. striata and A. reitzii, are found to cope with temperatures below freezing if kept dry over winter.

Most of the species (there are not many cultivated varieties) grown in the UK are small, rosette types that suit pot culture well and do not grow too large. A few begin as small pot plants but have the potential to become tall specimens - A. arborescens, A. bainesii or A. ferox, for example.

Aloe should be planted into a moderately fertile, free-draining medium, usually made up of loam mixed with materials such as coarse sand, crushed brick or perlite. They like a position in full sun, though the fierce summer sun can cause leaves to turn brown so a position that receives morning or late afternoon sun is ideal. If kept in pots, plants can be moved out during the frost-free months.

During winter they should be kept dry but not completely arid. During summer months, the compost should be given a thorough drenching, but then be allowed to dry again before re-watering. Plants will benefit from an occasional liquid feed during the growing season. They will probably need repotting every third or fourth year.

WHAT THE SPECIALISTS SAY

- Jeff Rowe, partner, Trewidden Nursery, West Cornwall

"My favourite is A. polyphylla, the spiral Aloe, which looks spectacular. It's an unusual species - it's on the Red List. It throws the book out of the window in terms of Aloe. It grows above the snow line on mountains in South Africa and likes to be damp all the time. We keep them in a tray of water during the summer. We had three plants in flower last year, so we are now raising more from seed.

"It's a fallacy that Aloe can only be grown as houseplants. If they're in pots they can obviously be taken outdoors in the summer. They look great on a patio or decking. They only need watering about once a week so they are the ideal plant for busy, working people.

"We grow several species that can tolerate low temperatures, down to -8 degsC. A. striatula is probably the hardiest species in the UK, but A. ferox, A. striata and A. reitzii also cope well. The biggest tip is to keep them as dry as possible during the winter, then they can cope much better with the cold.

"We grow them in a very free-draining, peat-free medium, and we can get away with leaving them on a remote site where they get watered occasionally, in a frost pocket, and they suffer very little damage."

- Gill Stitt, owner, Shrubland Park Nurseries, Suffolk

"The genus ranges from small plants to huge trees. In the UK the smaller types tend to be grown in the house, but there are some that might survive outside. A. vera is the commonest and is grown as a houseplant. Another one that is popular is the partridge-breasted Aloe, A. variegata.

"Other good species include A. ferox, which has big spines and becomes quite a large plant. Two that are borderline hardy are A. ciliaris and A. striatula. I've seen them in sheltered coastal gardens, and they get quite tall. A. plicatilis has lovely candelabra shoots and can become quite a large tree, but looks good as a small plant in pots. A. striata is one that has spectacular flowers - they are produced after around four to five years.

"As most Aloe come from southern Africa, they will die if they are wet and cold during the winter. So they generally need frost protection and a well-drained, gritty compost."

IN PRACTICE

- Mark Reeve, plant area manager, Coolings Garden Centre, Kent

"We usually display Aloe in our houseplant area but then some are put outside in the glasshouses during the summer, weather permitting. We sell around three or four varieties. I recommend A. vera and A. variegata (also known as the partridge-breasted Aloe or tiger Aloe), which is my personal favourite. I've found a lot of customers keep A. vera in their kitchen just in case they get burned on the cooker and can simply tear a leaf off and squeeze the gel onto the burn.

"We like to show off the plants by displaying them in glazed pots or alongside other succulents. Our customers like them because they are easy plants, needing minimum care and only the occasional watering."

SPECIES AND VARIETIES

- A. arborescens, or the krantz Aloe, is a half-hardy species with striking, grey-green spiny leaves arranged into rosettes on tall stems. It produces beautiful spikes of red or orange flowers in winter and spring. Grown as a house plant in the UK, but it can grow to 3m tall in warm climates.

- A. aristata Award of Garden Merit (AGM) (H1) is a robust little species that forms a dense rosette of dark-green leaves. The rosettes can reach up to 40cm across. A. aristata will not bloom readily indoors unless it receives enough bright light.

- A. bainesii is a slow-growing tree species that is grown as a houseplant in the UK but can reach 18m tall in its native country, South Africa. Orange, poker-like flowers might emerge in the summer.

- A. brevifolia AGM (H1), or the short leaf Aloe, is a stemless species forming tight rosettes of fat, white-teethed leaves. Offsets are freely produced and it can increase to form large clumps. Likes full sun to partial shade.

- A. broomii is a short-stemmed, robust species that forms a dense rosette of green leaves, with reddish-brown teeth along the margins. It has a tall, fat lower spike that can reach a height of 1.5m.

- A. ferox is a tree species that produces a single stem with large, fat succulent leaves and orange-to-red branched flowers in the autumn. It is often grown as a houseplant, but some grow it outside in well-drained soil in full sun and protect from severe frost. Height and spread: 2.5m.

- A. peglerae is stemless and clump-forming with rosettes of spreading, blue-green leaves curving inwards, with tiny white marginal teeth that turn to reddish brown as the plant grows older. It produces red flowers.

- A. polyphylla is one of the hardier species grown in the UK, tolerating down to -4 degsC. It forms a single rosette with a striking spiral arrangement of leaves. The leaves are grey-green with purplish-black tips. It has red-salmon-pink flowers on tall spikes. Tolerates cooler and damper conditions than other Aloe. Height: 30cm. Spread: 70cm.

- A. mitriformis is a low-growing species with sturdy, spiky-edged green leaves, graduating to purple at the tips. It produces branched spikes of orange-scarlet flowers in January and February. Tender, so often grown indoors as a houseplant. Suits Mediterranean and rock gardens, but if planted outside in the ground or in pots during the frost-free months, they will need to be moved inside before winter. Height and spread: 45cm.

- A. striata, or coral Aloe, forms handsome rosettes of blue-green leaves that lack the spines common on most Aloe. Instead, these types have a smooth, attractive, pinkish margin without any teeth. The species bears large rounded heads of bright coral-red flowers.

- A. striatula is one of the hardiest Aloe in the UK, tolerating down to -8 degsC. It has a branching habit and produces orange or yellow flower spikes in the summer. Likes well-drained soil in full sun. Height and spread: 1m.

- A. variegata AGM (H1) is an easy-to-grow succulent that forms dense clumps of rosettes with fleshy, dark-green leaves that are banded with white markings. In summer, each rosette produces tubular pink flowers. Tender, so grown as a houseplant in the UK. Height: 60cm. Spread: 25cm.

- A. vera AGM (H1) is a commonly available ornamental houseplant, as well as being the source of the medicinal gel that is used on burns. It forms dense clumps of fleshy, light-green leaves with soft-toothed margins. It is capable of producing spikes of tubular yellow to orange flowers in summer, but this happens rarely in the UK. Height: 60cm.


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