Orbea dummeri - Cactus Club

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Orbea dummeri

Plant of the Month > Species O to P

by Bruce Brethauer

           Orbea dummeri is an unusual and curiously attractive member of the greater Milkweed Family (Asclepiadoideae) with clustering mounds of succulent stems. Plants typically grow to about 4 inches in height, and will eventually spread to form low mats to a foot or more wide. Stems are branching, with long, pointed tubercles in two ranks. Typically, the stems have a pale grey/green coloration and are heavily marked with reddish purple dots, splotches and lines; but in very bright sunlight, the base color becomes more pale, to almost white with just a hint of green.

           These are typically summer bloomers, producing smallish starfish-shaped flowers high on the stems. On my plants, the flowers open to just under an inch across, but there is some variation in the size of flowers from plant to plant, and some plants may produce flowers to 2 inches across. Color varies from olive green, to nearly chartreuse, but in some online images, the flowers appear to be nearly yellow. The petals bear many papillae, each one topped with a stout, translucent/white hair. The corolla is nearly white, and includes the pollinia, and stigma.  I have noticed no significant scent to these flowers, either pleasant  or otherwise, which contrasts with the typically carrion-scented flowers of many of the other succulent members of the Asclepiadoideae

            Orbea dummeri is native to East Africa (S. Kenya, N. Tanzania, S. Uganda and E. Zaire): it grows in arid areas in Acacia-Commiphora bushland and Combretum woodland, and occasionally on exposed sites on rocky outcrops.  This is an easy plant to grow and flower in cultivation; it responds well to my general guidelines on growing succulents, with a few considerations. Plants grown indoors should be provided with as much light as possible - more is better: but if you are habit of moving you succulents outdoors during the warmer months of summer to benefit from sun, rain and warm temperatures, it would probably be best to site this plant where it will receive a bit of dapple shade - particularly during the hottest hours of the day. In habitat, this plant is dormant during the summer months; drought, extreme heat, and excessive exposure to intense light seem to be factors in inducing dormancy in this plant. Because this year's Summer weather has been unusually mild, and wet, my plant is showing no inclination to go dormant at this time; it gets full exposure to sun, but again, since our June and July  weather has been so rainy and cloudy, overexposure to the sun has not been a factor yet. In the meantime, its growth rate has been exceptional, and I fully expect to see it double or even triple in size this season, and it will probably produce a second wave of flowers as well. It appreciates a dry and cool winter dormancy - it would probably be best to maintain its winter temperature at about 50 degrees or so - cooler temperatures may make it susceptible to bacterial and fungal infestations - especially if it is exposed to humid conditions at this time. It should probably be watered no more than about once a month at this time. When temperatures rise again in spring, resume more frequent watering, and once growth begins, provide periodic fertilization. Because growth can be pretty rapid from Spring through early Fall, this plant would probably benefit from more frequent fertilization than slower growing succulents - perhaps as much as once every three or four weeks with a dilute fertilizer at this time. Keep an eye out for mealy bugs and any signs of fungal or bacterial infections - if any stems become discolored or turn mushy, trim these off and keep a close eye on this plant for any signs of additional issues - while I have not had problems with either fungus or insects, online sources suggest that this plant can be susceptible to these issues.

           Propagation is easy from cuttings. Cuttings can be taken at any time of year, however, for best results, it would be best to start cuttings in spring or early summer, when the plant is actively growing. Set aside a cutting for a few days for the end to heal, and lay the cuttings on the surface of the potting medium (not partially buried, with the stem inserted into the potting medium), and press these down so that there is good contact between the stem and the soil. Roots should be established in a few weeks to a few months - stem growth and branching will soon follow. It may also be possible to grow this plant from seed, although I am uncertain if this plant will readily self (two clones may be required for seed to set).

           Given the ease of care, the rapid growth rate, interesting qualities, and the smaller stature of this plant, I am surprised that it has not proven to be a more popular. I have never seen it offered in any of the "big box" nurseries, and even the specialist mail order nurseries seldom offer this plant. I acquired mine through Miles to Go, but it is occasionally available through Bob Smoley's Gardenworld. I suspect that it may occasionally be offered at various cactus society shows and sales. If you should ever come across this plant in your travels, give it a try - in my opinion, it is one of the most attractive and interesting plant of this genus.

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