Walnut Creek’s Ruth Bancroft is a national authority on drought-resistant gardening. Twice a month, she and her staff share their knowledge with Times readers.
Q: I bought an aloe plant last year at the Ruth Bancroft Garden, and the cold weather in January reduced it to a pile of mush. I liked the look of my aloe, but have been afraid to plant another one after this experience. My neighbor has an aloe in her garden and it survived last winter without problems. What would account for this difference?
A: There are hundreds of kinds of aloes, and they vary greatly in their size, appearance and ability to withstand cold. One particular kind, aloe vera, is especially well-known because of its medicinal and cosmetic uses. As a result, many people equate “aloe” with this one species, not realizing that there are a multitude of others, some with medicinal properties and others without such uses.
Among all these kinds, many are tropical and lack resistance to cold, while others have varying degrees of frost-tolerance. A few can endure temperatures down into the low 20s and even the upper teens, and these are safe bets for use in gardens in our area.
These include the shrubby Aloe striatula, the diminutive Aloe aristata and Aloe brevifolia, the somewhat larger Aloe maculata (synonym: Aloe saponaria) and Aloe glauca, the creeping-stemmed Aloe distans and the spiral-leafed Aloe polyphylla.
Many kinds can endure a few degrees below freezing, but get damaged after that. In such cases, it is possible to site them in the garden’s warmer spots to minimize the risk.
Since overhead cover helps to deflect cold air as it settles, a place under eaves or an overhead branch affords some protection. Because cold air sinks, the bottoms of valleys or ravines are prone to colder temperatures than slopes.
At the Ruth Bancroft Garden, we place wooden frames, covered with clear plastic, over vulnerable plants. These are left in place throughout the cold months. Alternatively, the gardener who keeps an eye on weather reports can drape frost cloth or other insulating material over sensitive plants when a cold front approaches.
Some commonly grown aloes in California do well through most winters without any special precautions, but can have their flowers ruined by freezes in extra-cold winters, or even sustain serious injury in the very coldest years.
Examples are Aloe arborescens, which forms a large shrub with spikes of scarlet flowers in winter, the stemless Coral Aloe (Aloe striata), and the candelabra-flowered Aloe ferox, which has a single large head of leaves, but develops a trunk in time.
These plants have a dramatic presence in the garden even when not in flower, and their colorful flowers brighten up the winter months, so we consider them well worth growing, even if we lose flowers once in a while in cold years.
We will have a variety of aloe species and hybrids at our fall plant sale on Oct. 13, and will have knowledgeable people on hand to answer questions.