Aloe vera

Identification and origin

Aloe vera belongs to the family Asphodelaceae; you may still see it under its old name, Aloe barbadensis. In the wild it is native to northern Oman, in the Hajar Mountains, where it grows in desert and dry scrubland. Cultivated since antiquity, it has since naturalized across much of the world’s warm regions, from the Mediterranean to the Caribbean.

It is a perennial with no visible stem that makes offsets at its base and slowly forms a clump. The leaves, arranged in a stiff rosette, are thick, fleshy and lance-shaped, and can reach 18 in long. They start out green with white flecks and turn gray-green as they age; the edges carry small whitish teeth. In a pot it usually stands 12 in – 2 ft tall and can approach 3 ft. On mature plants at least three years old, an upright stalk carries tubular yellow, sometimes orange, flowers; indoors it only blooms in very good conditions, in a very sunny window or outdoors in summer. On an old aloe, it is normal for the outer leaves to droop a little and sprawl away from the center.

Light

Full sun suits it best; it adapts to light partial shade but needs bright light to flower. Indoors, choose a window that gives it at least six hours of sun a day, and turn the pot now and then so it grows straight. Too little light shows quickly: leaves stretch, flatten and go limp, and the rosette flops. If no window is bright enough, a grow light set 6–12 in above the plant and left on fourteen to sixteen hours a day gives good results. If you move it outside for the summer, acclimate it gradually: going straight from shade to full sun scorches the leaves.

Watering

Aloe stores water in its leaves and handles drought and dry indoor air well, so it is better to err on the dry side. During the growing season, from spring to early fall, wait until the mix is dry all the way down, then water thoroughly until it runs out the bottom, and empty the saucer about fifteen minutes later. From fall through late winter the plant rests: cut back sharply, giving only enough to keep the roots from drying out completely and the leaves from shriveling. Keep water out of the center of the rosette and do not mist the leaves. Soft, bleached leaves point to too much water; yellow, shriveled leaves to too little.

Potting mix

A coarse, fast-draining mix is essential. A cactus and succulent mix works; you can also combine equal parts potting soil, sand and perlite (or lava rock). A thin layer of perlite or coarse sand on the surface helps keep the base of the plant dry. Always use a pot with large drainage holes; unglazed clay, which lets the mix dry faster, is ideal.

Temperature

By day it is happiest at 61–75 °F; nights can be cooler, around 50–61 °F, and a clear drop in temperature at night suits it. It cannot take frost. Avoid long spells below 50 °F: if it summers outdoors, bring it in during early fall, before nights fall below that mark, and shelter it from heavy rain. In winter, kept dry, it can briefly tolerate down to 39 °F. Watch out for windowsills, which are often much colder than the rest of the room: a chilled plant discolors. It can only live outdoors year-round in USDA zones 10a to 12b.

Repotting

Repot about every two years to refresh the mix and make room for roots and offsets; for older plants, midsummer is the best time. Choose a pot that leaves 1–2 in between the root ball and the side, and never go up more than two pot sizes at once: a large volume of soil stays wet and invites root rot. Replant at the same depth, with the leaves just above the mix and the base not buried.

Pruning

Aloe does not really need pruning. Remove dry or damaged outer leaves at the base to keep the rosette tidy and give mealybugs fewer places to hide. If you harvest leaves for their gel, always take the outermost, oldest ones so the plant keeps growing from the center; then cut away the outer part of the leaf and keep only the gel.

Propagation

The easiest method is to separate the offsets (pups) that appear at the base of mature plants. Wait until they have several sets of leaves, unpot the mother plant, find the point of attachment and cut it with a sharp knife. Plant each pup in its own small pot of fast-draining mix and water sparingly while it roots. A large clump can be divided the same way at repotting time.

Common problems

The same symptom can have several causes: always check light, watering and temperature before treating anything.

• Root and crown rot: caused by overwatering or a mix that does not drain; it is often fatal.
• Flopping rosette: too little light (limp, flattened, stretched leaves) or too much water (bleached, weak leaves). Some drooping of the old outer leaves is normal.
• Yellow, shriveled leaves: not enough water; a cold spell can also discolor the leaves.
• Mealybugs: white cottony clusters hiding deep in the rosette or on the roots. Dab them off with a cotton swab dipped in rubbing alcohol and check the plant regularly.
• Other pests: scale, aphids and aloe mites. The sticky honeydew some insects leave behind encourages sooty mold, a black film on the leaves.
• Leaf diseases: leaf spot and aloe rust, which starts as small yellow spots that turn brown and is favored by cool, humid conditions.

Toxicity

Toxic to dogs, cats and horses. The leaves contain anthraquinones and saponins; eating them causes vomiting (except in horses), lethargy and diarrhea. In people, swallowing leaf material causes abdominal cramps and diarrhea, sometimes with reddish urine: the leaf sap is a strong laxative, and its latex can irritate skin on contact. Only the gel inside the leaf is considered safe; neither people nor pets should eat the rest of the plant. Keep it out of reach of pets and children and, if it has been eaten, call a veterinarian or poison control.