Cultivation Notes on Euphorbia (Part 1)

About the genus

The genus Euphorbia consists of over 2,000 species that have very different modes of growth. They can range from small geophytic plants (underground tubers) to small and large sized shrubs right up to large trees several metres high.

Euphorbia cremersii
Euphorbia cremersii – a Typical Geophytic Form

Their habitat range is also quite extensive and various species can be found on each of the five major continents. The majority of the plants of interest to the succulent enthusiast are found on the African mainland, the island of Madagascar and the Arabian Peninsula.

Euphorbias are rarely grown for their flowers as these are usually very small. The whole flower structure can be quite complex but, in most cases, there are additional leaves known as cyathophylls complementing the flower make up. E. pulcherrima for instance, from which our well-known Christmas Poinsettia is derived, can exhibit quite large colourful leaves below the main flower structure.

Most species are summer growing although there are some exceptions which come into their own at the latter end of the year and that require more careful cultivation.

Euphorbia milii
Euphorbia milii

How to grow them

Madagascar is the fourth largest island in the world and the Tropic of Capricorn runs right through the south-western town of Tulear. It follows therefore that any plants endemic to Madagascar require a certain amount of heat to survive.

An ideal cultivation temperature would be in the order of 16–17°C, and it would be unwise to allow temperatures to fall below an absolute minimum of 10°C to reduce the possibility of losses over winter. If the minimum temperature cannot be maintained then the easiest solution is to bring the plants into the living room over winter and treat them as house plants.

Generally, geophytic plants (those with subterranean tubers) are grown partially out of the growing medium, the premise being to stop any chances of rotting. The tuber can be completely buried but ensure that the growing medium is a very well-drained mixture that will not hold a lot of water. Plants whose tubers are completely buried should produce much stronger leaf formations during the growing season.

Euphorbia aureoviridiflora
Euphorbia aureoviridiflora

The growing season for most Madagascan species is from spring through to late autumn. During this time the plants will need to be well watered, starting from the time the first leaves appear and gradually reducing the amount of water when leaves start to wither, turn brown and fall. Plants can be kept dry over winter unless the higher temperatures mentioned above are maintained, in which case a light watering can be given once a month.

Plants will respond to being fed during the growing season with something like a half-strength Chempak or Tomorite solution with every second watering.

A lot of Madagascan euphorbias grow in shady places such as under bushes and shrubs so it can be beneficial for the plants to be in semi-shady positions rather than full sun all the time.

As with many genera, some species are easier to grow than others and as a general rule the shrubbier types are easier than the geophytic types which are now more difficult to come by. It should still be possible to maintain a nice collection of some wonderful Madagascan plants with those that are readily available.

Text and photos: Bob Potter

No part of this article may be reproduced without permission. Copyright BCSS and the Author 2022

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