Cacti and Succulents
Succulent Euphorbias native to hot, arid climates (some 850 of the 2000-odd Euphorbia species) require good light and well-drained soil. Many thrive in full sun, though some may scorch, and benefit from ground-level shade.
Most Euphorbia species can be grown from seed. Several observations should be made. First, some species are dioecious, i.e. have male and female flowers on separate plants. That is, to produce viable seed, plants of both types are required. Use a fine-tipped brush to transfer pollen from the stamens of one plant to the stigma of another. Note: nursery-purchased specimens are likely to have been reproduced vegetatively, from cuttings, and thus will typically be of only one sex.
Second observation: Euphorbias disperse their mature seeds rather explosively. Paint the ripening seed capsule with a layer of white glue to prevent seed loss.
Finally, Euphorbia seed does not remain viable long; sow immediately in sterile medium, at 70-80F/21-27C, and keep moist. Protect from full sun, and decrease watering once seedlings are established.
Cuttings taken in spring or summer provide the simplest way of propagating most Euphorbias; cut at branching species at a joint. Dip in cold water until the latex stops flowing, and allow the cutting to callus, at least several days for leafless species. Rooting hormone can be helpful; pot in sterile medium, protect from full sun, and water infrequently.
Note: Euphorbia latex can be very irritating. Handle with care.
Root rot is a significant risk to succulent Euphorbias: water infrequently, and rarely in winter or lower-light conditions. Fertilize only using low-nitrogen preparations; larger, fast-growing species will need repotting every few years.
Tropical species typically hardy only in zone 10; some north and south African species can tolerate temperature dips as low as freezing, especially if their roots are dry.
Euphorbia grandicornis (cow's horn)
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