Diosma (Coleonema)

How to choose a diosma

The White Diosma is Coleonema album, a bright green shrub with white flowers that grows to about a metre and a half if left unclipped. The Golden Diosma is grown as much for its yellow gold foliage as for its flowers, and stays lower and more compact, which makes it a favourite for edging and for contrast against dark green plants. The Compactum Pink Diosma is a compact pink flowered form of Coleonema pulchrum, and the Red Velvet Diosma is a named variety with more strongly coloured flowers.

For a clipped low hedge, choose one variety and plant it all the way along so the line grows evenly. For a mixed border, the golden form gives colour all year.

Where diosma grows

Diosma suits temperate and cool climates: Melbourne, Adelaide, Perth, Canberra, Hobart, Sydney and the tablelands. It tolerates moderate frost, wind and some coastal exposure once established. It also grows in the subtropics if drainage is excellent, but it tends to be short lived in humid summers, and in the tropics it is not worth attempting.

Full sun gives the densest growth and the most flowers. In shade the plant opens up and becomes leggy. It is used with other evergreen shrubs in borders and foundation plantings, and it is one of the reliable plants for cool climates. You can browse all our shrubs for companions.

Diosma has naturalised in parts of southern Australia, so do not plant it beside bushland, and never dump prunings in or near a reserve.

Planting and spacing

Plant in autumn or spring in soil that drains freely. On clay, raise the bed or plant on a mound, because diosma dies quickly with wet feet. A light, slightly acidic soil is ideal. For a low hedge, space plants 50 to 60 centimetres apart; as individual rounded shrubs, allow about a metre. Water in well and mulch, keeping the mulch clear of the stem.

Care basics

Water through the first summer. After that diosma copes with ordinary dry spells in temperate areas, though a deep soak in long hot periods keeps the foliage fresh. Feed lightly in spring after flowering with a controlled release fertiliser; it does not need much.

Pruning is what keeps diosma dense. Trim lightly all over as soon as flowering finishes in late spring, taking off the spent flowers and a little of the new growth. Never cut back into bare wood, because old stems without leaves seldom reshoot and the gap stays. A plant trimmed lightly each year from the start stays compact for many years; one left alone for several seasons goes woody at the base and is usually better replaced than cut hard.

Common questions

When does diosma flower?

From late winter through spring, generally July or August to October depending on the district, with a few flowers at other times.

How big does diosma grow?

The taller pink and white kinds reach about a metre and a half high and wide if left unpruned. Golden and compact forms usually stay under a metre.

Can I cut diosma back hard?

No. It rarely shoots from bare wood. Trim lightly each year after flowering and keep the cut within leafy growth.

Why is my diosma dying in patches?

The most common cause is root rot from poor drainage or overwatering, which shows as sections browning off. Improve drainage before replanting.