Euphorbia decidua
| Light | Bright light to gentle sun; a little shade in the hottest part of the day |
|---|---|
| Water | Sparingly in growth; keep completely dry once the branches drop and it goes dormant |
| Soil | Very gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Best kept frost-free; warm summer growth, cool dry winter; roughly USDA zones 9b–11 |
| Propagation | Seed; sometimes grafting |
| Toxicity | Toxic; milky latex is irritating to skin, eyes and if ingested — keep away from pets and children |
Euphorbia decidua is a small caudiciform succulent from south-central Africa that stores water in a fat, partly buried tuber and sends up slender, spreading branches which it sheds each year as it enters dormancy. The name decidua — "deciduous" — refers exactly to this habit: for much of the year the plant is little more than a knobbly tuber sitting at soil level, only pushing out its thin, angled branches when conditions are right. It is one of the more sought-after of the tuberous euphorbias among collectors of caudex plants.
Description
Euphorbia decidua grows from a large, elongated (obovoid) underground tuberous root that swells with stored water and forms the plant's main body, tapering below into a long taproot. In habitat this caudex sits mostly buried, with only its crown showing; in cultivation many growers raise it a little to display the fattened base.
From the top of the tuber the plant produces thin, ridged, spreading to trailing branches, three- to four-angled and often armed with small persistent spines along the angles. These branches are the deciduous part of the plant — they emerge in the growing season and wither and are shed as the plant moves into its dry rest, leaving the bare tuber behind. Small cyathia (the specialised euphorbia "flowers"), the pale green involucres marked with a red centre, appear toward the tips of the branches during growth. As with all euphorbias, every part exudes a milky white latex when cut.
Distribution and habitat
The species is native to south-central Africa, ranging from southern Tanzania and the Democratic Republic of the Congo south through Zambia, Malawi and Zimbabwe to north-western Mozambique, where it grows in seasonally dry miombo woodland. There it experiences a warm, wet growing season followed by a long dry period — the cue for it to drop its branches and retreat into the tuber until the rains return. Plants typically root in well-drained, often gritty or rocky ground where the tuber can stay relatively dry when dormant.
Cultivation
Euphorbia decidua is grown much like other tuberous, seasonally dormant succulents: the key is to respect its rhythm and never keep it wet when it is resting. Pot it in a very free-draining, mostly mineral mix and give it bright light, with a little protection from the fiercest midday sun.
Water regularly but moderately while the branches are actively growing, always letting the mix dry between waterings. As the plant naturally begins to shed its branches, taper off and then stop; keep it completely dry and frost-free through its dormant period. A wet, cold tuber rots quickly, so err on the dry side, especially in winter. See Watering and Repotting for general technique, and handle the plant carefully — the latex is an irritant.
Propagation
Seed is the usual and most reliable method, sown onto a warm, gritty surface much as for other euphorbias; see Propagation — seed. The thin branches do not root readily and the plant is not freely offsetting, so vegetative propagation is uncommon. Where growers want to bulk up or speed a plant along, grafting onto a compatible euphorbia rootstock is sometimes used, though grafted plants lose the natural tuberous character that makes the species appealing.
Common problems
- Tuber rot — by far the commonest cause of loss, almost always from watering during dormancy or from a slow-draining mix. A dormant tuber should be kept dry.
- No branches / stays dormant — often simply the season, but persistent failure to break can indicate the plant is too cold, too wet, or exhausted; keep it warm and dry and wait for the growth cue.
- Pests — mealybugs (including root mealybugs on the tuber) and the occasional spider mite are the usual offenders; check the caudex and roots at repotting.
See also
- Euphorbia — the genus overview
- Grafting · Soil and potting mix · Watering · Repotting · Propagation — seed