Asclepiads are members of the milkweed family (the Apocynaceae) and are found in many areas from Africa, the Middle East and into Asia. There are many genera and species but relatively few are seen for sale except from specialist sources. Some of the genera you are most likely to come across are Stapelia, Orbea, Duvalia, Huernia, Caralluma, Brachystelma, Ceropegia and Fockea.
The flowers of many are both unusual and spectacular. Some are called carrion flowers because of the foul smell that they produce to attract pollinators but there are also sweetly scented members of this group.
Most asclepiads come from very arid areas but many will thrive in cultivation given some heat and care with watering. The majority of these plants prefer warmer conditions than most cacti but although some require a minimum winter temperature of 12°C, some of the species, particularly those that originate from South Africa, will survive at 5°C. Generally however these plants are best kept at about 8–10°C, and bottom heat, provided by a soil warming cable, within an airy propagator is ideal. If it is not possible to provide this temperature in the greenhouse, the plants can be brought inside for the winter and placed near a window (making sure they are inside any curtains at night).
During the growing period a bright sunny position is required with good ventilation to prevent sunburn. It is useful to remember that many of these plants are found under bushes and in rock crevices in their natural environment so that there is some natural filtering of the high light intensity.
Use a coarse, very free-draining compost for these plants, adding at least the same quantity of grit to soil. Some growers of these plants are now using pure grit or coarse gritty sand or inert material such as Seramis with good results
Asclepiads require regular watering throughout the summer but must not become waterlogged. Always ensure that the soil has dried out from the previous watering before wetting them again. Most losses occur from overwatering.
Propagation of clumping asclepiads is easily achieved by cutting off small, often already rooted, stems and allowing the cut surface to dry for a few days before repotting again. This is also useful practice as plants become larger as it is the outer, newer growth that tends to produce the flowers. However some of the asclepiads do not clump and these need to be propagated from seed. General succulent seed lists often include only a few asclepiads, so if you want more choice, it would be worthwhile seeking out specialist growers.
Pests and diseases
Mealy bug is a major pest of asclepiads so inspect your plants regularly for them. Mealy bugs tend to congregate at the base of the stem just above the roots but control can be achieved with a good contact insecticide. It is important to always carefully examine new plants before placing them in your collection.
Another problem associated with asclepiads, particularly stapeliads, is their tendency to develop a fungal disease. This usually occurs if plants are kept too cold or damp. The fungus develop as black patches in the stems of the plants. It is important to cut off the damaged tissue as soon as it is seen. Treatment with fungicide may be helpful but there is no specific cure.
A full set of cultivation leaflets are given free to new members and are available for sale in our shop.
Images: Bill Weightman (1, 5, 6, 7, 8, 9), Chris Moore (2, 3, 4) and Tina Wardhaugh (10)