Plant of the Month: April

Caltha palustris Common name: Kingcup, marsh marigold, cow lily Family: Ranunculaceae Vital statistics Height and spread: 30 - 60cm (12 - 24in) x 40 - 60cm (16 - 24in). Form: Herbaceous perennial Soil: Rich, boggy soil at the water's edge. Aspect: Full sun. Hardiness:  Fully hardy.

Caltha palustris @ Rosemoor

Growing along the margins of Rosemoor's Stream and Bog Garden, Caltha palustris brings a lovely splash of spring sunshine to the early months of the year. In the same area we also have specimens of C. palustris's rather more sophisticated cousins, C. palustris var. alba (white flowers) and C. palustris 'Flore Pleno' (smaller, fully double yellow flowers).

Caltha

This genus contains approximately 12 species of deciduous perennial, marginal water plants, bog plants and rock garden plants that are grown for their attractive flowers, and are similar in appearance to buttercups.

They are widespread in temperature regions of both hemispheres.

The leaves are kidney to heart-shaped, fleshy, and bright to dark green with sturdy stalks.

The cup-shaped flowers range in colour from white through pale yellow to gold and have five tepals (more in the double-flowered forms). They flower from February to April and sometimes have a second flush in late summer. Caltha are one of the earliest perennials to flower.

The plant was once used medicinally and named verrucaria because of its supposed ability to cure warts. It is now considered too toxic for such use.

Caltha palustris

Palustris means marsh-loving, hence this species is found in shallow water or bogs. Plants nearest water flower earlier, probably due to the fact that their roots experience less frozen soil. Its leaves are kidney-shaped, dark green, toothed and 4 - 10cm (1.5 - 4in) long.

In spring, bright golden-yellow, waxy flowers, 4cm (1.5in) across and very similar in appearance to buttercups are borne on upright stems, 30 - 45cm (12 - 18in) tall.

'Flore Pleno' has double yellow flowers with greeny-yellow centres and a height and spread of 25cm (10in).

Caltha palustris var. alba is compact, clump-forming and has single white flowers

AGM

The RHS Floral A Committee awarded Caltha palustris an Award of Garden Merit and described it as: Rhizomatous herbaceous perennial to 60cm, with rounded, rich green leaves and clusters of deep yellow flowers 4cm wide.

The RHS Floral A Committee awarded Caltha palustris 'Flore Pleno' an Award of Garden Merit and described it as: Rhizomatous herbaceous perennial to 30cm, with dark green, rounded leaves and clusters of long-lasting, very double, bright deep flowers.

Cultivation

Caltha palustris is a marginal or marshland plant which thrives with its feet wet, but likes them to be well anchored. Having some at the water's edge and some further away is desirable as it spreads the season of flower.

Prone to powdery mildew.

Propagation

Propagation is by division at the end of the summer or very early in spring so as not to spoil the season's display.

Sow seed as soon as it is ripe and keep damp.