Aloe petricola
| Light | Bright light to full sun once established |
|---|---|
| Water | Moderate in the growing season; keep dry and rested in winter |
| Soil | Gritty, free-draining mineral mix (see Soil and potting mix) |
| Temperature | Best above freezing; tolerates brief light frost when dry, USDA zones 9–11 |
| Propagation | Seed; division only where plants have clustered (uncommon) |
| Toxicity | Generally regarded as low toxicity; sap may irritate |
Aloe petricola is a robust, stemless aloe from the summer-rainfall regions of northeastern South Africa, named for its habit of growing among rocks — the epithet petricola means "stone-dweller," giving it the common name stone aloe. It forms a large solitary rosette of broad, blue-green, spotted leaves edged with dark teeth and bearing scattered prickles on the leaf surfaces, and is prized for its striking bicoloured flower spikes of coral-red buds that open to greenish-white (yellow in some forms), giving the raceme a two-toned appearance.
Description
Aloe petricola grows as a stout, stemless (acaulescent) rosette, in time reaching around 45–60 cm tall and up to roughly 1 m across. The fleshy leaves are broad and lance-shaped, dull blue-green to grey-green, and usually marked with scattered pale spots that are more prominent on younger plants. The leaf margins carry firm reddish-brown teeth, and mature leaves frequently bear scattered spines (prickles) on the leaf surfaces, especially the lower surface — an unusual feature that helps distinguish it from many spotted relatives.
In winter the plant sends up several tall, densely flowered racemes, often branched, on stout stems well above the foliage. The unopened buds are red to coral, while the opening tubular flowers turn greenish-white (yellow in some forms), so each spike shows a clear band of colour from tip to base. The prominently exserted stamens give the open portion of the raceme a fuzzy, bottlebrush look that is very attractive to sunbirds and bees.
Distribution and habitat
The stone aloe is native to the Mpumalanga province of northeastern South Africa, where it has a restricted range around Nelspruit (from Sabie to Barberton) and grows on exposed rocky outcrops, ridges and grassland slopes. As its name suggests, it favours shallow, gritty pockets of soil among rocks in an open, sunny, summer-rainfall climate, enduring hot wet summers and cool dry winters. Though locally common where it occurs, its range is limited; it is assessed as Least Concern and is not considered threatened.
Cultivation
Aloe petricola is an undemanding, rewarding plant for growers who can give it sun and sharp drainage. Plant it in a gritty, mostly mineral mix and grow it in bright light to full sun, which keeps the rosette compact and encourages good flowering; too much shade leads to a loose, pale plant. Water moderately through the warm growing season, letting the soil dry between waterings, and keep it much drier through winter to mirror its natural dry rest — though note that in cultivation it flowers in the cooler months, so it should not be left completely bone-dry when spikes are forming.
The species handles heat well and tolerates brief, light frost if kept dry, but it is safest above freezing; in colder climates grow it in a container that can be moved under cover. See Watering and Repotting for general technique.
Propagation
Stone aloe is grown mainly from seed, which germinates readily when sown fresh on a warm, gritty surface and kept lightly moist. Being a solitary or only sparsely clustering species, it seldom offers pups; where a plant does form a clump, mature rosettes can sometimes be separated by division. Fresh seed and hand-pollination give the best results, as the showy flowers are readily worked by pollinators outdoors.
Common problems
- Rot — the usual cause of loss, from overwatering or a poorly draining mix, especially over the cool winter months.
- Etiolation — grown too dark, the rosette becomes loose, elongated and pale, and flowering suffers.
- Pests — watch for mealybugs deep in the leaf axils, scale on the leaves, and aloe mite, which can cause abnormal galled growth around the flowers.
See also
- Aloe — the genus overview
- Soil and potting mix · Watering · Repotting · Propagation — seed · Pests and diseases