by Bruce Brethauer
Kalanchoe tomentosa is an attractive plant, with very succulent, heavily felted leaves and stems. Plants have a grayish, to silvery-white coloration, with characteristic chocolate-brown to nearly black markings along the tips and edges of the leaves. The stems are branching, typically ramifying from the base; established plants will eventually grow to about 24 inches tall, and spread to about as wide, or somewhat wider. These plants have a broad appeal, and are readily available from any nursery which offers a good selection of cactus and other succulents. These make good house plants, and are especially useful in succulent patio planters, succulent wreaths, and living walls, as this is an easy plant to grow, it mixes well with other leaf succulents, and the grayish-white coloration of this plant acts as a nice foil, helping to accentuate plants with more colorful foliage.
The Kalanchoes belong to the Crassulaceae, or Crassula family, which includes such familiar genera as Sedum, Sempervivum, Crassula, and many others. While the majority of other members of the Crassula family have flower parts in multiples of 5, the flowers of Kalanchoes have parts in multiples of 4, with 4 sepals, 4 petals, 8 stamens, and 4 free (not united) carpels. These traits can be seen in the following image of the flowers of Kalanchoe daigremontiana.
The flowers of Kalanchoe tomentosa , while small and not especially showy, are interesting, in that the outer petals are also densely covered with with felt. Plants which are grown exclusively as a houseplant will seldom produce flowers: flower production requires warm temperatures, and very bright light. To increase the likelihood of of flower production, this plant should be moved to the patio in spring and summer to benefit from increased temperatures, and exposure to full sun.
This species is native to Madagascar, frequently growing on granite and gneiss outcrops. The heavily felted leaves and stems are an adaptation to drought, and are especially effective in reducing water loss through evaporation in exposed and windy sites. In other plant species, heavily felted leaves are often an adaptation to higher elevations - the felt may help to protect these plants from excessive exposure to ultraviolet light. In habitat, this species occurs at elevations between 3900 and 5200 feet.
Over the years, a number of select cultivars have been introduced, these varying mostly in details of the shape, size, and density of the foliage, or the overall size of the plant. "Chocolate Soldier" is the most popular of all, with broader regions of color on the leaf tips and margins, with colors that range from a radiant rusty brown on new growth, and gradually maturing to a more chocolate-brown coloration. Some online sources also indicate that "Chocolate Soldier" is a more reliable plant with a faster growth rate than the species.
My general guidelines are a good starting point for the basic care of this plant: always remember to provide as much light as possible year round - otherwise you risk weak and rather leggy looking growth. I move my plants outdoors from spring, through summer, and into fall to benefit from higher temperatures, and increased light levels. Normal rainfall will provide more than adequate moisture at this time, but make sure that this plant is given an extra gritty potting medium which drains and dries out quickly - perpetually wet soil will kill this plant. During this time, this plant will benefit from regular applications of dilute fertilizer - I use a lower nitrogen "bloom booster" type - both Peters or Miracle Grow have worked well for me. I mix these at about 1/3 the indicated strength, and make monthly applications in spring and summer; other growers may fertilize somewhat more frequently - some as often as every 2 weeks in the summer. When temperatures drop to the lower 40's in fall, I bring my plant inside, and maintain it under cooler and drier conditions. While this species will tolerate brief periods of temperatures into the lower 40's and even into the upper 30's, sustained cold and long periods of cold and wet conditions can kill this plant, and a frost will kill it outright. Temperatures from the mid 60's to the mid 50's would would probably be best for the winter dormancy of this species. This plant should also be provided with good air circulation year round, especially during hot and muggy conditions - under these conditions, molds and mildews can become established in the felted laves. It should be mentioned that the lower leaves are shed as the plant grows; while this is normal, in time, this can result in a plant with long stems topped with rosettes of leaves. Pruning will encourage branching, and will result in plants with a fuller appearance.
Propagation is easy, plants can be established by rooting cuttings - while larger cuttings will establish faster, it is also possible to establish new plants by rooting a single leaf. In either case, cuttings should be taken, (and rooted) in late sprig through summer, while the plant is actively growing. Established plants are readily available from a number of sources: I acquired my plant through The Glasshouse Works, but it is frequently offered through such area growers as Groovy Plants Ranch, Bakers Acres Greenhouse, Oakland Nursery, Botanica (the gift shop at the Franklin Park Conservatory), and is frequently offered in the cactus and succulent selections of any number of "big box" nurseries
While I have never noticed any issues with insect pests on my own plants, some authorities suggest that mealy bugs can be an issue, and recommend that growers keep an eye out for this pest - keep in mind that the heavily felted leaves provide a nearly perfect camouflage for this pest. It should also be mentioned that some species of Kalanchoe are toxic if ingested - while none of my resources have indicated any toxic issues with this species, it would be wise to prevent any accidental ingestion of any parts of this plant.
These issues aside, Kalanchoe tomentosa is an attractive, easy to grow species which is widely available, spineless, and compact enough to be grown as a houseplant, yet large enough to be grown in a mixed succulent summer planter. With the growing popularity of living walls, I anticipate that this species (as well as many other succulents) will prove to be especially popular- its attractive appearance, easygoing nature, and drought tolerance will secure its place in many succulent collections.