Bowiea volubilis, the "Climbing Onion" - Cactus Club

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Bowiea volubilis, the "Climbing Onion"

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by Bruce Brethauer

       In a group of plants known for its many interesting curiosities, Bowiea volubilis is one of the great curiosities of the succulent world. It produces large onion-like bulbs which may measure from a few inches upwards to as much as 10 inches across (most of the plants which I have seen will produce bulbs from 2½ to 4 inches across). The bulbs, like onion and tulip bulbs are comprised of tightly clustered modified leaves which serve as reserves of nutrients and moisture. Depending upon growing conditions, the bulbs may be uniformly pale green, or may be covered or partially covered with the dried remnants of outer leaves (much like an onion skin). In time, these bulbs eventually split to produce two bulbs: over a period of many years, some plants can produce numerous offsets, while others will tend to remain solitary, only producing offsets after its bulb has grown quite large.



       Periodically, plants will produce long "vines", which are actually the plant’s inflorescence, which in this species are intricately branched, and are either climbing or scramble along the ground and onto nearby plants. These "vines" can grow quite large (in some plants, upwards of 15 feet in length). These do not produce true tendrils or other structures which may anchor or attach the vines to other plants, so the vines can only stay in position by weaving their way through the stems of other plants. In cultivation, it is best to provide this plant with a trellis or other vertical support so that the inflorescence can grow more upright, otherwise its growth will be scrambling, and may tangle through nearby plants in you collection, making it difficult or impossible to move or rearrange them. This inflorescence produces many dozens to hundreds of tiny flowers, shaped like six pointed stars with greenish to greenish-white petals. The flowers are reminiscent of onion or garlic flowers, but this species is in the hyacinth family, and is not closely related to the onion family. Some growers report that these flowers readily set seed, which self sew into nearby pots, producing many new seedlings. To date, my plant has never set seed (perhaps different individuals are less likely to set seed than others) but plants can readily be propagated by dividing some of the bulb offsets. It may also be possible to induce the formation of numerous bulbils beneath the surface leaves by maintaining extended drought conditions. These bulbils can later be extracted to establish additional plants, but since this procedure unduly stresses the parent plant, and will take a noticeable toll of its health and appearance, I do not recommend this as a propagation technique.



       Bowiea volubilis responds well to basic succulent care, with a few minor differences. First of all, most authorities insist that this species demands warm conditions, with temperatures maintained above a minimum of 50 Fahrenheit year round. This does not reflect my experience - This plant seems to respond well to a cool winter period of dormancy, and my plant has survived exposure to very cool periods outdoors prior to the time that it was moved inside. In at least one instance, it has survived light frost. Also, I have found that growing specimens of this plant - especially those which are growing their vining inflorescences - require more frequent watering than most other succulents, and should not be subjected to extended drought at this time (unless you want the plant to go dormant and loose its "vines"). I have found it best to feel its bulbs at this time to determine the need for watering - if the bulbs are very turgid, they can probably wait, but I they seem at all soft, give them a good watering. I have found that this plant is an opportunistic grower, and will grow, and produce its "vines" whenever growing conditions are to its liking. Scorching heat and drought will quickly put this species into dormancy. The inflorescence will become dry, and will eventually fall away, and the bulbs will become covered with a papery envelope of dried leaves (similar to the outermost skin of an onion). Even if more favorable growing conditions are provided immediately, it will usually take at least several weeks before this plant will break dormancy again. Keeping the plant dry and cool through the winter will keep the plant dormant, but if it is kept wetter and warmer, it will tend to grow continuously, even through the winter months.



       The literature seems to be divided on whether or not the "onions" grow at the ground’s surface or underground in habitat. I have seen more than one reference state that in habitat, these plants produce underground bulbs, with only the vining inflorescence growing above ground. This has been confirmed by Bill Hendricks who has observed plants in habitat during his trips to South Africa. These same references stated that it is only in cultivation that these plants are grown with their bulbs exposed. In my experience, seed grown plants will readily produce their first bulbs on the surface of the ground, or with their bulbs only half buried, so this may be a trait which is influenced by environmental conditions - perhaps in wetter and cooler conditions, plants may be somewhat more inclined to produce their bulbs at ground level, while those growing in hotter, drier conditions will be more likely to produce their growth underground. At any rate, all of the plants in cultivation which I have observed are grown with these bulbs exposed - and are probably grown in this manner as a precaution against rot - besides, growing these plants with their bulbs exposed definitely creates a bit more visual interest.

       Several varieties, or possibly, different species have been suggested for this genus. At present it appears as though most authorities only recognize the single species Bowiea volubilis, but occasionally, additional names may be seen in the trade - and sometimes these names are used quite arbitrarily - but it is my understanding that the plant identified as Bowiea volubilis tends to produce larger "bulbs", and is slower to produce offsets. Bowiea nana tends to produce smaller bulbs and is more likely to produce clusters of bulbs. Bowiea gariepensis is a more robust plant, producing larger bulbs, and larger, thicker vines. It is also suggested that flower colors may also vary slightly.



   Unfortunately, this is not a plant for every grower - in spite of its superficial resemblance to onions, the "bulbs" of Bowiea volubilis are not edible - they produce a powerful cardiac poison, and should never be ingested by people or animals - so care should be taken when growing this plant to prevent children and pets from getting close access to it. Aside from this drawback, this is an interesting and attractive plant, and is quite easy to grow, well worth a place in any succulent collection.


 
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