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The following notes are mainly based on my limited experience with Asclepiadaceae (Brachystelma, Ceropegia, Fockea, Huernia Hoodia, Stapelia / Orbea etc.) grown in a south-east facing conservatory in North-West London, England. Different climates, facilities and genera may well allow or require a different approach, and I would welcome contributions to this page from other growers, particularly of the more difficult genera. However, the owner of this page cannot accept liability for any plant loss, or damage or personal injury arising from use of information included here.
Cultivation notes - from a damp English climate
Most Asclepiads enjoy warm conditions, and appreciate regular application of water (and fertiliser) in hot summer weather providing that the plants are in their growth phase. For some of the more difficult Asclepiads, heat is a requirement and watering should be more circumspect. I always use rain water, and tend to water over the top of most plants - after all that is how it happens in habitat ! However, many growers prefer to water plants from the bottom (simulating drier conditions where the roots seek underground moisture), and a careful approach to watering is essential for difficult or rare plants. The air is kept moving gently in my growing space by a small ex-computer fan and this ensures that water on the plants dries off rapidly as most succulent plants, and especially Asclepiads, resent prolonged soggy conditions. It is a good idea to allow the compost to dry out between waterings, and if the weather goes cold in the middle of the summer, then stop watering ! Much of the reputation that Asclepiads have for rotting unexpectedly is probably related to watering plants too early in the year while still dormant, or when the weather is uncertain, or to attack by other pests such as root mealy bug, the damage from which allows disease into the tissues.
A heated tray or propagator under the plants may help with over-wintering, although some species (e.g. Ceropegia, Fockea, Huernia, Piaranthus, Stapelia / Orbea) tolerate cool winter temperatures (40°F) if kept absolutely dry. However, if kept dry during the winter to avoid rotting in cool conditions, rehydration in the Spring requires care, as the roots may have died. Brachystelma tubers should be kept absolutely dry (50°F) when not producing vegetative growth, and in my conditions this usually includes the winter months. However, brachystelma tubers may also dry out beyond recovery if overwintered dry in warm conditions, and the best solution for this sort of plant is to keep them in continuous growth in warm conditions e.g. a propagator.
Asclepiads seem to do best in very free-draining gritty compost (mine are also in clay pots) which helps the compost to dry out between watering. Peat-based composts, with lots of sharp sand and grit works well, but peat also encourages root-mealy bug and I now use garden compost-based mixtures diluted with sand and grit, which are "sterilised" in a large stainless steel tin in the oven (248°F for 2 - 3 hours). This treatment gets rid of bugs and their eggs, but the compost is not sterile in a clinical sense.
I also like to have a layer of grit (ca. 1cm) under sensitive or difficult plants, so that they are not sitting on a damp substrate. The roots will strike through the grit into the soil perfectly happily, but the base of the plant or tuber stays dry. A grit top dressing also discourages algae and mosses, buildup of salt crusts on the soil surface, and helps to prevent the compost from washing out when watering. However, if you grow in plastic pots, top dressing may increase the time that the compost stays wet after watering.
Always remove dead plant material (dead flowers, leaves, stems) from your growing space, as otherwise in damp weather it will become colonised by fungi and rapidly become a source of spores, which may in turn infect your asclepiads.
Pests of asclepiads . . . also see Pests & Diseases
Please remember that all insecticides, fungicides and some other horticultural chemicals are very toxic to people, and handle with extreme caution - rubber gloves, face mask and goggles are advisable.
If a plant that was growing well suddenly goes into a decline, suspect root-mealy bug. This pest destroys the roots, preventing proper uptake of water, so the plant looks under-watered even though it is sitting on soggy compost. Probably the damage also helps fungi to enter the tissues, and the next stage is a rotten plant. Root mealy bug may be combated with a good systemic insecticide.
Ordinary mealy bugs are also a major problem with Asclepiads, and are difficult to eliminate from crevices between the stems. Mealy bugs can be spread through a collection by the wandering vegetative growth of tuber-forming Ceropegias. Scale insects are said to be a major pest of Asclepiads in some climates.
With the withdrawal of dimethoate from sale in EC countries, the only really effective systemic insecticides for domestic use are those based on Imidacloprid marketed in the UK as "Provado". The same chemical is available under other names elsewhere, so check the small print on labels. This water-soluble granular powder is added to water used to used to irrigate plants which then take it up throught the roots and become toxic to most pests that feed on any plant parts. Imidacloprid appears to be effective against most pests of asclepiads (but not against red spider) when used as directed. So far, I have seen no adverse effects on a wide range of succulent plants. It remains to be seen how long it will take for mealy bugs to develop resistance, but at present Imidacloprid offers the real possiblility of clearing them out of a collection.
It is a good idea to take cuttings from suspect plants that are not thriving, clean off obvious infestation and start off some new plants
in case the original can not be saved. The cutting and compost should be treated prophylactically with imidaclorprid. Brave growers may
also like to try grafting onto e.g. Ceropegia tubers.
There has been some discussion on the Internet of watering routinely with antibiotic solutions to discourage fungal rot. One could also water with systemic fungicide. However, my personal view is that this is not a good idea except possibly while raising seedlings, and may lead to antibiotic/fungicide -resistant strains of fungi and bacteria, against which there will be no defense. Even worse, micro-organisms can exchange genetic material responsible for resistance, and it is conceivable that this could lead to antibiotic resistance in organisms which are harmful to humans or animals.
In addition, antibiotics, fungicides and insecticides are also very toxic - one exploits the differential toxicity between diseases and their hosts, but this does not mean that the host will not also suffer from prolonged treatment. Copper-based fungicides can accumulate in the soil to toxic levels.
Many Asclepiads are readily grown from seed, and some people grow plants of the faster growing species to flowering size from seed each year, thus avoiding problems of overwintering. However, the seed of many species (e.g. Stapelia sp.) has a limited life expectancy, and should be sown fresh. I find that cactus and succulent seed is best sown into "sterilised" compost in semi-sealed containers, and watered with a fungicide (Benlate or Nimrod T) until the seedlings reach the "pricking-out" stage.
Those species with fleshy stems are easily propagated from portions of the plant laid flat on a gritty potting mixture, when they will produce roots from the underside of the stems. Planting stem cuttings vertically seems generally less successful (an exception is the vine-like Ceropegia species e.g. C. radicans), and the portion of plant embedded in the compost is prone to rot rather than root. Tuber-forming Cereopegias can be propagated from small tubers formed at joints in the thin stems. Regular propagation of plants with a few cuttings seems to be the best insurance against loss of the main plant.