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Plant Highlight: Aloe arborescens

December 2010

Aloe arborescens is a familiar part of the horticultural landscape in the warmer parts of California, including the Bay Area.  The term “arborescens” means “becoming a tree”, and indeed this species develops a branching woody stem in time, but its normal form is that of a bush rather than a tree.  Mature plants are typically large rounded many-headed clumps with toothy leaf edges.  The form commonly grown here has cone-shaped spires of scarlet flowers in the winter months, peaking in December to February.  However, many people do not realize that this plant has other variants with differing flower colors, and one of these is a yellow-flowered form.

At the Ruth Bancroft Garden, our yellow plants of Aloe arborescens are usually the first to come into flower, commencing in November.  At the bud stage, the flowers are yellow with green tips, and when open they are a pale yellow color.  Aside from the flower color, the plants look identical to the red-flowered ones.  Plants of either color are quite free-flowering, and a mature many-headed specimen can have dozens of flower heads, making for a splendid show.

The sword-like tapering leaves of Aloe arborescens are green to gray-green, and can reach a length of up to two feet (60 cm).  In full sun the leaves tend to be shorter and more curved back, often with a tinge of dull red in the hot summer months, while in shadier situations they are longer and greener.

Aloe arborescens has an extensive natural distribution in southern Africa, from Zimbabwe and Malawi in the north down through the eastern parts of South Africa, and then westward in a strip along the coast almost to Cape Town.  In the northern and eastern parts of its range, rainfall is concentrated in summer, but westward towards Cape Town the rainfall is year-round.  In cultivation, plants adapt well to our winter rainfall, and they require little irrigation in summer.

Plants can be easily grown from cuttings, which is the usual method of propagation.  They are not fussy about soil type, though good drainage is recommended.  When it comes to cold tolerance, plants can endure temperatures down to the mid-twenties Fahrenheit (about -4° C) without injury, provided this is not sustained for too long.  In the low twenties plants are likely to show some leaf damage, and they can be killed if it gets below 20° F (-7° C).  Although plants are not threatened by lows in the range of 27° or 28° F (-2° to -3° C), the flowers can be damaged, so frost protection (such as covering the plant with frost cloth) is advised.