Euphorbia horrida Boiss.
Growth Habits: A clumping spiny plant that throws offsets, mainly from the base. Initially when young, the plant resembles a globular cactus, but as it ages it can reach a height of 3ft. (75 cm.) and a girth of approximately 4 inches (10cm.) or more. When young it is very much like a cactus with its handsome spines (which are in fact the dried remnants of flower stalks) but of course closer examination shows that it has no areoles and therefore cannot possibly be a cactus. When the plant is young the spines have a beautiful purple tinge and the body a fresh green appearance, although there is a cultivar with a greyish tinge to the body. As the plant ages, like the rest of us it loses its initial handsome appearance and is not as appealing (to me anyway). There are many varieties of this species, perhaps natural hybrids between it and taller Euphorbias, giving rise to the big, spiny forms like E. horrida noorvalescens.
Scientific name: Euphorbia horrida
Common names: African Milk Barrel
Etymology: The genus Euphorbia was established by Linnaeus in 1753 and commemorates Euphorbus, the 1st century physician to King Juba II of Mauritania, who is thought to have used plants, such as Euphorbias, as medicine. The specific name horrida means frightening.
Origin: South Africa (lower Great Karoo)
Light: Will accept anything from light shade through to full sun
Compost: A normal open compost is more than adequate for this plant. You can if you wish make it a little richer than for some of the cacti species, but do not overdo it or the plant will lose its natural characteristics.
Water: Moderate watering in summer will ensure that the plant stays true to type. Too much water will either kill the plant by rotting at the base or if the weather is conducive to growth the plant may ‘bolt’ and outgrow its normal proportions.
Flower: As with 99% of Euphoprbia the flower is small, yellow and insignificant. Up to five fertile and sterile peduncles appear on a single flowering eye, these "spines" can be 40 mm long, the main spine develops from a sterile peduncle.
Fruit: The fruit is a capsule, typical of the Euphorbia genus.
Min. temp: The average minimum temperature should be around the 50°f. (10°c.) but mature plants are said to be hardy to 25°f. (-4°c.) for short periods of time. Personally I would not like to risk so low a temperature, particularly if the air is humid.
Cultivation: Established plants of Euphorbia horrida are easy to grow and will in fact stand quite a bit of neglect. Getting them established is however not always easy. If the atmosphere is very humid, cutting tend to rot before they have rooted
Habitat: The Karoo is a semi arid plateau of South Africa. The Karroo, where irrigated, is very fertile. Livestock grazing is important there, and citrus fruits and grains are raised. The name is also applied to the low scrub vegetation found in semi arid regions
Comments: I always like to have a few different Euphorbia in the greenhouse. There diversity of shape and colour is a big attraction, although some of them over time take up too much room so it is always as well to have one or two young plants ready to replace their older relatives. Always be aware that the sap, a milky latex liquid is poisonous and they should not be handled with open wounds on the hand and keep fingers and hands well away from the eyes after handling them. It is as well to know when taking cuttings that in some species the sap is under some pressure and will squirt out when the epidermis of the plant is pierced.