Tillandsia bulbosa "Air Plant" - Cactus Club

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Tillandsia bulbosa "Air Plant"

Plant of the Month > Species T to Z

By Bruce Brethauer

   As a rule, I try to restrict myself to discussions about succulent and desert plants in the Plant of the Month section, but this month I have taken a few liberties. In the strictest sense, Tillandsia bulbosa is not a succulent plant, even though its leaves and bulbous base give the plant a very succulent appearance; like many succulents, it is also a very easy plant to grow, and will tolerate a greater degree of drought and neglect than a number of other Tillandsia species, so people could be forgiven for assuming that it may be a succulent plant.

   The Tillandsia species are widely distributed in the tropical and subtropical Americas, from Florida, Georgia, Louisiana, Texas, and south throughout Central America, and much of South America (occurring as far south as central and possibly into southern Argentina).  Tillandsias belong to the Bromeliaceae, or bromeliad family, which includes the pineapple, Earth Stars (Cryptanthus), Urn plants (Aechmea), Billbergia, Abromeitiella, Dyckia and many others. As a rule, the Tillandsias are comparatively small plants, typically with individual rosettes growing from a few inches to perhaps 18 inches tall. A few species grow larger, and virtually all species will offset to produce large clusters containing many plantlets. While a number of species are terrestrial, growing in soil, most of the Tillandsias which are commonly seen in cultivation are epiphytic, growing on branches of trees, on rock surfaces, and other substrates without any need of soil. The roots of most species provide little more than an attachment to branches and other substrates, and are not the primary means by which plants absorb water and nutrients. Dew, rainwater and dissolved nutrients are primarily absorbed through the leaf surfaces of most species. Many species produce a covering of many minute hairs (trichomes) which gives many Tillandsias a grey to silvery appearance. Trichomes may assist these plants in capturing and absorbing moisture. In some species, the covering of trichomes is so dense that plants have a rather felt-like appearance and feel. The entire genus is often referred to as "Air Plants", a reference to their epiphytic lifestyle, but contrary to this common name, the Tillandsias need a bit more than just air alone in order to thrive. Tillandsias are remarkably easy to grow, tolerating a bit of benign neglect, and will grow under a variety of conditions. With a bit of of attention to their specific requirements, it is possible to maintain these plants for decades, producing large "colonies" with many plantlets, and annual flower displays which in many species is quite spectacular.

   Tillandsia bulbosa is quite a distinctive species, producing large bulbous bases measuring from about 1 to perhaps 2 inches across in most clones but in some clones these may grow larger, with some plants producing gigantic bases reputedly measuring to 9 inches in circumference, and reaching 18 inches in length. The leaves are narrow, and curled in at the edges to produce straw like tubes, which are oddly twisted and contorted, giving plants a rather weird appearance. I have grown at least two different clones of this species; one is a larger clone with comparatively large bases and extremely long leaves (some approaching 8 to10 inches in length), while the other plant produces shorter leaves to barely 3 inches in length and with somewhat smaller bases (to just under 1 inch across). When flowering, the uppermost leaves become brilliantly colored in scarlet tones, and the erect flower scape is red and very short; the tubular flowers have bright violet petals. The flowering plants are exceptionally attractive, but as is typical of the bromeliads, this species is monocarpic, with each rosette flowering once and eventually dying afterwards. Invariably, this species will produce several basal offsets at about the time that the main rosette flowers, so the plant will not be lost after it has flowered: in time, a very large plant will eventually be produced as these offsets proliferate. Tillandsia bulbosa is native to the West Indies, southern Mexico, and much of Central America, and south to Colombia and eastern Brazil. It typically grows in dense masses on trees in open woods, in dense forests, in mangrove thickets along the coast, and on lianas on the shores of rivers from sea level to an altitude of 5,000 feet. This species appears to favor habitats which are in the very least seasonally very wet, and benefits form high humidity when grown in cultivation.

   One of the most unusual features of this plant is that in the wild, ants will often colonize its bulbous bases. Contrary to its appearance, these bases are not solid, but are mostly hollow, and are divided into a series of internal chambers, which ants will utilize as living spaces, nurseries, etc., for their colonies. The plant benefits from this relationship, as ants will provide some protection from various herbivorous insects, and will also fertilize the plant, which absorbs nutrients from the detritus left by the ant colony. Ants may also assist in pollinating the flowers, however, the bright coloration of the flowers and floral bracts would suggest that other animals (probably birds and/or butterflies) are the primary pollinators of these flowers. As a rule, there are only a few species of tropical ants which are known to colonize this species in the wild, however, in one summer, one of the plants which I had moved outdoors to benefit from sunshine, warmer temperatures and high humidity was colonized by one of our local species of ants, proving that such relationships are not necessarily species specific. Growers here need not worry about inadvertently introducing castaway ants into their households, as nursery grown plants will have been treated with insecticides, which would eliminate all ants.

   This species grows best when provided with bright filtered light, warm temperatures, and high humidity, and seems to produce its best growth during the long days of summer. While most authorities would recommend against it, my plants have produced their best growth when grown in a nearly sealed aquarium under terrarium-like conditions with high humidity - conditions which would probably not be tolerated by many other Tillandsia species (which would generally require less humid conditions). Grown in areas with less humidity and more air movement, this plant will benefit from frequent misting - especially during the warmer months, when it produces most of its annual growth. Tillandsias should be provided with bright, diffuse light; either filtered sunlight, or grown under full spectrum fluorescent lights (it is best to grow Tillandsias within about 1 foot of a fluorescent light, as this will provide both adequate light, and additional warmth). While this species seems to appreciate very high humidity, ideally, it should also be given adequate air circulation to prevent conditions which could promote the growth and spread of molds and fungus. Even though this species may experience monsoonal rains in habitat, it should never be maintained under perpetually wet conditions, which would inevitably result in the death of this plant. Instead, plants should be frequently misted (several times per week, or better still, they should be given a light daily misting) and should be watered well about once every week or two. I usually water my Tillandsias by placing the entire plant into a tub of water, leaving them in the tub from several minutes to several hours to absorb water. When removing plants from the watering tub, always shake off any excess water, either returning the plant to its growing area, or placing it temporarily in a somewhat drier location so that excess water may evaporate. Most growers suggest fertilizing tillandsias about once every month or two by mixing a bit of water soluble fertilizer into its water. One of the all-purpose fertilizers with a 10/10/10 or 20/20/20 ratio of nutrients is recommended; this should be diluted to about 1/4 the recommended strength; I would also suggest that the fertilizer should include a complete balance of the so called trace elements - minerals and nutrients which plants require in minute quantities. After the Tillandsias have been soaked in this fertilizer solution, the remaining fertilizer can be used to water other household plants. Whenever possible, plants should be kept fairly warm (80 to 85 degrees or so during the day; and cooler (room temperature) at night) - when plants are continually maintained at room temperature, growth may slow to a crawl.  I'm not certain what conditions initiate flowers in this species, but I suspect that cooler temperatures and /or shorter daylight hours may play a factor, as my plants have always flowered in the late fall and winter months. While the flowers can easily be pollinated to set seed, I have not yet attempted to germinate Tillandsia seed, and cannot offer any specific advice on how to propagate it by this means. Typically, additional plants are propagated by dividing the offsets produced at the base of the mother plant.

   Tillandsias have fallen in and out of vogue over the years, and while I am seeing a bit of renewed interest in these attractive and curious plants, they are still a bit harder to find than they were a few years ago, when it was nearly impossible to go to a nursery without seeing a selection of Tillandsias glued to driftwood, seashells and refrigerator magnets. I prefer to grow plants which are unmounted, as it is often difficult to maintain these plants when they have been permanently mounted to shells and magnets (plants grown on refrigerator magnets seldom see enough daylight or moisture to grow well, and plants attached to shells frequently fall victim to mold due to water puddling on the inside of the shell). It has always been a challenge to locate un-mounted and properly identified Tillandsias in most nurseries, but now that Tillandsias seem to have fallen a bit out of vogue, it is nearly impossible to do so. A few nurseries may offer baskets of mixed (unidentified), un-mounted Tillandsias, and a few specialist mail order nurseries offer labeled and un-mounted plants.

T. bulbosa is common enough that it is frequently seen in Tillandsia assortments, and has been intermittently available, both mounted and unmounted, locally at Oakland Nursery, - but it may also be encountered at other nurseries as well. Mail order nurseries which specialize in Tillandsias will invariably keep this species in good numbers, although it is still very difficult to find the exceptionally large clones of this species.

   Tillandsia bulbosa is a distinct plant with no real look alike species that it may be easily confused with: if you see a plant which looks like the plants illustrated here, it is almost certainly  this species (Tillandsia caput-medusae has a similar appearance, with an enlarged, bulbous looking base and contorted tapering leaves, but that species is covered with a thick coating of felt-like trichomes which gives it  a whitish coloration and fuzzy texture). Good sized specimens - those comprised of many clustered heads - are a memorable sight, and a large cluster in full bloom is unforgettable. This species is so curious, and so easy to grow, that I am amazed that it is not encountered more frequently in collections. In my humble opinion, this is an excellent plant for young and novice growers, as it is both an unusual plant, with a distinctive appearance, and it is a very forgiving species, which will tolerate a fair amount of neglect. It has proven to be very resistant to insect pests: even when other plants in my collection fell prey to white flies and mealy bugs, I have never seen evidence of these pests on this plant. Unlike many other plants in my collection, this species will never need to be repotted, and will never require any sort of a potting medium. Much of the regular watering and fertilization can be delivered by a misting bottle, and while plants will benefit from brighter light and rather warm temperatures, they can be easily maintained at room temperatures near a window. A good sized plant has the appearance of a modern sculpture: all in all, it is a plant which I recommend highly.

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