Aloes are native to the Old World regions of Africa, Arabia and Madagascar. They are generally found in arid and semi-arid climes with a range of habitats from forests to grasslands to rock faces to deserts. Some grow near the coast at sea level, others can be found at 8,000 feet of altitude. They come in all shapes and sizes, from miniature species a couple of inches tall to towering trees that might be 50 feet or more in height. A plant can be solitary in habit or sucker to form clumps, shrub-like or tree-like with a single trunk while others are pendulous cliff-hangers. Aloe leaves generally have toothed margins, though not always, and can be green, red, purple, blue-gray, spotted, striped, shiny or rough. Their flowers might be red, yellow, orange, pink, white, greenish or bi-colored. Many are a different color in bud than when open.
Most aloes are considered leaf succulents, the exception being the grass aloes. They form rosettes much like agaves but they differ from agaves in that they flower year after year whereas agaves generally flower once in their life upon reaching maturity and then die. An agave flower stalk is terminal; aloe flower stalks do not come from the terminus but always grow laterally, sometimes with several stalks each bloom period.
In the landscape, they provide winter color either with their flowers or, in the case of some species, by turning red with temperature stress. Although many aloes bloom in the winter, others bloom a little later in the early spring, while some bloom in the summer and others almost year-round. Most are not technically considered winter growers, flowers notwithstanding. Those which are truly winter growers do not do well in the Valley area as they are from areas that receive no summer rains. Our monsoon season is a killer for those species with its high nighttime temperatures and increased humidity.
Aloe flowers attract not only hummingbirds but Verdins and Cactus Wrens as well. They can be somewhat promiscuous and you might find volunteer plants coming up in odd places in your yard. Seed produced will usually be hybridized unless you pollinate yourself and enclose the flowers with netting to keep other pollinators at bay.
Aloes are among the easiest plants to grow and, like most succulents, require good soil drainage. Most also demand filtered or afternoon shade in the low desert, depending on the species. Once planted in the ground, they usually do not need to be fertilized. The biggest problem occurs in the months of August into September when the monsoon is in effect. The stomates or pores in the leaves of many succulent plants, including aloes, open at night when the air is supposedly cooler. The Valley’s night temperatures at this time are now consistently above 90 degrees with high humidity for long periods of time, prohibiting the plants from transpiring. This causes some species to rot, sometimes appearing to do so overnight. Watering during this time should be almost subsistence watering. Ideal watering practices would be overhead watering rather than drip irrigation as this will wet the entire root systems, which can be widespread and shallow.
Arizona usually starts cooling down gradually for the winter, giving our plants a chance to become acclimated to the cooler weather. It is not unusual to have a couple of months with low temperatures in the 40’s and 30’s. Then when we do have a freeze, our plants can usually withstand temperatures down to about 28 degrees F. The duration of these lower temperatures and the amount of humidity present play a key role in determining whether an aloe will succumb, assuming the plant is healthy to start with.
In Africa, there are all manner of pests that attack aloes: mites, weevils, scale, grasshoppers. The biggest problem here is the aloe mite, which has become more and more prevalent, causing a cancer-like growth on the leaves and flower stalks. The mites are difficult to treat, and some of the best pesticides are not available to the homeowner. If mites are discovered on an unimportant plant – throw it away. Otherwise, treat with a systemic miticide, repeating the application in two weeks.
Never assume all aloes are medicinal. Some contain compounds in their leaves that are akin to rat poison, another has been called the suicide aloe because it is supposedly poisonous if ingested.