Round-leaved sundew

About this plant

Drosera rotundifolia is the sundew most people in northern countries will have met in the wild. The rosette is usually 4 to 10 cm (1.5 to 4 in) across; each leaf is a round blade, 6 to 12 mm (0.25 to 0.5 in) wide, on a slender stalk 2 to 9 cm (1 to 3.5 in) long, covered in red tentacles tipped with mucilage. Small flies and midges stick to the leaves and are slowly digested. In summer a thin stalk carries a one-sided row of small white flowers, each with petals 6 to 10 mm (0.25 to 0.4 in) long, which open only in full sun. In early autumn the plant stops producing ordinary leaves and forms a tight bud of small scales at the soil surface, called a hibernaculum, in which it passes the winter.

This is the plant on which Charles Darwin did most of the experiments in Insectivorous Plants (1875). He began in 1860 after noticing how many insects the sundews on a Sussex heath had caught, and over the following years showed that the leaves respond to minute quantities of nitrogen-containing substances and secrete a digestive fluid comparable to gastric juice.

It grows in acidic sphagnum bogs, fens, wet meadows and lake margins across the northern hemisphere. It is still common in many regions but has declined where bogs have been drained, and it is protected in some countries; never collect plants from the wild.

Light

Give it full sun. In habitat the plant grows in open moss with nothing shading it, and in cultivation it colours red and grows compactly only in strong light. A shaded or indoor plant stays green and weak.

Water

Keep the medium permanently wet with mineral-poor water. The tray method with a deep tray, or planting in an outdoor bog container that never dries, both work. In the wild the plant can grow with its crown at the waterline, and it is worth flooding the pot now and then during hot weather. This is not a plant that tolerates drying out.

Growing medium

Living sphagnum moss is the natural companion and an excellent medium, as long as the moss is kept trimmed so it does not swallow the plant. Long-fibre sphagnum or a peat and sand mix both work. No fertiliser.

Temperature

The species wants cool to mild summers and a cold winter. Prolonged periods above about 30 °C (86 °F) weaken it, and in hot climates it is often lost by late summer. Provenance matters here: a species this widespread varies in how much heat it takes and how long it rests. Plants from central Europe tolerate warmer conditions than Californian ones, and stock from coastal northern California, southern Europe or Japan is the best choice for mild climates and greenhouses. Keep a note of where your plants came from. Winter temperatures near or a little below freezing suit the hibernaculum; it survives being frozen in a bog that is frozen solid, and it can be grown outdoors in USDA zone 9 and colder.

Dormancy

Required, and this is the main difficulty for indoor growers. The plant must be allowed to form its winter bud in autumn and must then be kept cold, roughly 0 to 5 °C (32 to 41 °F), and only just damp; the species expects about six months of dormancy, matching the half-year it spends resting in habitat. Outdoors in a temperate climate this happens naturally. Indoors, the dormant bud can be kept in a refrigerator in slightly damp sphagnum inside a bag, checked monthly for mould. The resting bud usually has no roots, which is why it can be lifted and moved so easily and why dormancy, not the growing season, is the time to transplant. Growth resumes when the bud is returned to light and warmth in spring.

Feeding

Outdoors the plant catches its own prey. Feeding is rarely needed and tiny leaves are easily damaged by over-large food.

Repotting

Repot in early spring as the bud begins to open, setting it so that the base of the bud sits in the medium rather than on top of it. Established clumps can be divided then. The species is also straightforward from seed sown on wet sphagnum and given a cold period.

Common problems

Decline in summer heat and rot during a warm, wet dormancy are the two common ways to lose this plant. Both come back to the same point: it is a plant of cold bogs and does best where its growing season is cool and its winter is cold.

Species-specific notes

Several similar temperate sundews are sold, including Drosera intermedia and Drosera anglica, which have longer, spoon-shaped leaves. All share the need for a cold dormancy. The round-leaved sundew crosses with both where they grow together: with D. intermedia it forms D. × beleziana and with D. anglica it forms D. × obovata, both sterile hybrids that are larger than either parent and can only be propagated by division or leaf cuttings. D. anglica itself is thought to have arisen long ago as a fertile hybrid between D. rotundifolia and D. linearis.