Tree aeonium

Identification and origin

Aeonium arboreum belongs to the family Crassulaceae, like the jade plant. It is native to the Canary Islands and Morocco; a few wild populations survive on the Atlantic coast of Morocco. It has naturalized in many mild-climate regions, around the Mediterranean, in California, and in New Zealand. The genus name comes from a Greek word meaning “ageless.”

It is a shrubby, freely branching succulent in which every stem ends in a rosette of fleshy, waxy, spoon-shaped leaves tipped with a small point. In the wild type they are glossy green and take on coppery tones in strong light. As the rosette makes new leaves, the oldest ones dry and drop, so mature plants carry their rosettes at the ends of bare stems. These stems are thick but brittle, and they put out roots wherever they touch the soil. Fully grown, the plant reaches about 3 ft tall and can climb to 5 ft; in a container it stays much smaller.

Mature rosettes send up a flower stalk about 8 in long carrying a conical cluster of small, starry yellow flowers from late winter into spring, and bees visit them. Each rosette dies after it blooms; because the species branches, the plant keeps growing from its other stems.

Many plants sold under this name are really hybrids. The most common cultivars are ‘Zwartkop’ (also spelled ‘Schwartzkopf’), with glossy leaves of a purple so dark they look black; ‘Atropurpureum’, reddish purple in sun; ‘Albovariegatum’, edged in white; and ‘Luteovariegatum’, edged in pale yellow with pink tints.

Light

This plant needs direct sun. Outdoors, give it full sun or lightly filtered sun; in very hot regions, keep it out of scorching afternoon sun. Indoors it only succeeds in a very bright window, ideally facing south or west, where it gets at least six hours of sun a day.

Watch the rosettes: if the plant stretches and loses its compact shape, it needs more light. In purple cultivars, poor light also turns the foliage green again, while strong light keeps the dark color even in winter. On the other hand, a red-brown tinge on leaves exposed in summer signals sunburn: move the plant a little farther from the glass. Moving it abruptly from the house into full sun also scorches it, so in spring get it used to the outdoors gradually over about two weeks, avoiding midday sun at first.

Watering

In its native habitat the plant grows mainly in fall and spring, and rests through the hot, dry summer. In cooler climates it often keeps growing in summer. During active growth, water deeply, until water runs out of the bottom of the pot, then let the mix dry out completely before watering again. Fifteen minutes later, empty the saucer: the shallow roots should never sit in water.

Taper off watering gradually at the end of the season. In winter, kept cool, give only enough water to stop the leaves from shriveling. Too much water is the main danger, because it causes root rot.

Potting mix

It needs a very porous, fast-draining mix: a cactus mix, or a peat-free, soil-based potting mix with added grit. You can also blend regular potting mix half and half with perlite or pumice. In the ground, a raised bed helps carry water away. In a container, a drainage hole in the bottom is essential.

Its nutrient needs are low. Only during active growth, two or three feedings of a balanced liquid fertilizer, or a cactus fertilizer at half strength, are enough for the whole season. Avoid high-nitrogen fertilizers.

Temperature

By day it is comfortable at 61–75 °F, and like most succulents it appreciates nights noticeably cooler than the days. In winter, a bright rest at around 50 °F, kept nearly dry, suits it perfectly; keep it away from radiators and heating vents.

It cannot take frost. If it spends the summer outdoors, bring it in before nights fall below about 39 °F. In the ground it is grown in USDA zones 9a to 11b. It also dislikes intense heat, during which it slows down or goes dormant, so water less at those times.

Repotting

Repot when roots fill the container, just as growth resumes, into a pot only slightly larger. An oversized pot keeps the mix wet for too long and encourages rot. Spring is the best season. Handle the plant gently, since its stems snap easily and its roots are fine.

Pruning

No pruning is required. Simply remove spent flower stalks and dead rosettes after blooming. If the plant gets too tall or leggy, cut off the terminal rosettes with a piece of stem to keep it more compact; the rosettes you remove make good cuttings. Doing this also delays flowering, and therefore the death of those rosettes.

Propagation

Cuttings are the easiest method, from spring through summer. Cut off a rosette with a few inches of stem, let the wound dry and callus for at least three days, then set the cutting on coarse sand or a well-drained soilless mix. Keep it warm, around 64 °F, and barely moist until it roots.

Side offsets can also be separated from the parent plant. Seed can be sown in spring at 66–75 °F.

Common problems

• Soft rosettes, a plant in decline: root rot from too much water or a poorly draining mix, especially when cool in winter.
• Lower leaves drying and dropping: normal leaf turnover, or dormancy during intense heat.
• Shriveled leaves in winter: the plant is too dry; a light watering is enough.
• A rosette dying after it blooms: normal behavior for the species.
• Red-brown tinge or dry patches on leaves: sunburn, often after a move into full sun that was too sudden.
• Stretched rosettes, dark cultivars turning green: not enough light.
• Pests: aphids, mealybugs, scale insects, and spider mites; keep an eye out for ants as well.

The same symptom can have several causes: always check light, moisture in the mix, temperature, and the condition of the roots before acting.

Toxicity

No toxicity is reported for this species by the veterinary and medical references consulted. The plant does not appear among the species listed as toxic to dogs, cats, or horses.