Why Are My Watercress Leaves Curling?

Aphids

Aphids are the most common cause of leaf curling on watercress grown outdoors or in a greenhouse. Peach-potato aphid (Myzus persicae) and cabbage aphid (Brevicoryne brassicae) both colonise watercress, preferring the growing tips and undersides of the small, rounded leaves. The leaves at the shoot tips curl and pucker tightly around the feeding colonies and may be sticky with honeydew. Watercress is in the brassica family, making it attractive to many of the same aphid species as cabbages.

What to do

• Inspect growing tips and leaf undersides regularly from April onwards. Spray affected shoots with insecticidal soap or a jet of cold water from a hose. Natural predators (ladybirds, hoverfly larvae) provide effective control outdoors. Because watercress is eaten raw, rinse harvested leaves thoroughly regardless of treatment method.

Heat and bolting

Watercress bolts in warm conditions, producing small, curling leaves and white flowers as the plant shifts from leafy to reproductive growth. Once bolting has started it cannot be reversed: the leaves become progressively smaller and more peppery, and the stems toughen. The UK growing season for leafy watercress is typically March to May and September to November; summer crops in exposed, sunny positions almost always bolt by June.

What to do

• Grow watercress in a cool, north or east-facing position in summer. Pick regularly, cutting shoots well down to discourage flowering. Cut back bolted plants hard in late summer; they often produce fresh leafy growth as temperatures cool in August and September. Sow successively every 3 to 4 weeks to maintain a harvest of young, tender growth.

Drought

Watercress requires its roots to be in constant contact with water or saturated growing medium. In a container, if the water level drops and the roots dry out even briefly, the leaves collapse and wilt within hours. Recovery is usually quick once the container is refilled, but repeated drying stresses the plant and accelerates bolting.

What to do

• Grow in a container without drainage holes, or in a tray that holds water. Top up the water daily in warm weather. In a garden, grow in a permanently moist position such as beside a pond, in a bog garden, or in a stream margin.

Watercress leaf beetle

Watercress leaf beetle (Phaedon cochleariae) is a small, dark, iridescent beetle whose larvae and adults chew holes in watercress leaves. Severe infestations cause significant leaf damage and may cause some distortion of young growth, though outright leaf curling is less typical than with aphid feeding. The beetles are most active from spring to midsummer.

What to do

• Inspect leaves for small holes and the tiny (<3mm) dark beetles or their larvae. Handpick adults and larvae where practical. Grow under fine mesh to exclude adult beetles. No insecticides are approved for watercress leaf beetle on edible crops in the UK; physical exclusion is the most effective method.

Frequently asked questions

Why are my watercress leaves curling?

Watercress (Nasturtium officinale) leaves curl most commonly because of aphid infestation, heat stress, or drought. Watercress is a semi-aquatic, cool-season plant that thrives in cold, moving water and begins to struggle when temperatures exceed 20°C. Aphids (particularly peach-potato aphid and cabbage aphid) colonise the growing tips and undersides of the small, rounded leaves, causing them to curl and pucker around the feeding colonies. Heat above 20°C causes watercress to bolt (run to flower), and in the process the leaves become small, curl, and turn peppery and bitter. Drought causes rapid wilting and curling: watercress requires constant moisture at the roots, and even brief drying out causes collapse. Watercress leaf beetle (Phaedon cochleariae) chews holes in the leaves and may cause some distortion in severe infestations.

How do I grow watercress in the UK?

Watercress (Nasturtium officinale) grows naturally in cold, clear, fast-flowing streams across the UK and can be cultivated at home in several ways. The simplest method for most home growers is a container approach: place a wide, shallow container (a seed tray or large pot without drainage holes) in a north-facing or dappled-shade position, fill with a moisture-retentive growing medium, and keep it topped up with water to keep the roots always submerged or at least saturated. Watercress can also be grown as a semi-hydroponic crop with the container sitting in a tray of water that is changed regularly. Watercress from a supermarket can be rooted in water and then grown on; place the stems in a glass of water in a cool, bright spot until roots form (usually within 1 to 2 weeks), then transfer to a moist container. Sow seed directly into wet compost from March to September. Harvest regularly to prevent bolting: cut shoots leaving 5 centimetres to regrow.

Why is my watercress bolting?

Watercress bolts (runs to flower and seed) when it is exposed to warm temperatures or long days. Bolting is the plant's natural reproductive response and cannot be stopped once triggered: the plant puts its energy into flower and seed production rather than leafy growth. Bolted watercress produces small, curling leaves, white flowers, and a progressively more peppery, bitter flavour that many growers find unpleasant. In the UK, watercress bolts most readily from late May to August when days are long and temperatures are high. To extend the productive leafy season, grow watercress in a cool, shaded, north-facing position; pick regularly to discourage flower formation; and sow successively every 3 to 4 weeks from early spring and again in late summer for autumn harvests. Some bolted watercress can be cut back hard and will produce fresh leafy growth if temperatures cool, particularly in late summer and autumn.

Is it safe to eat wild watercress from a stream?

Wild watercress growing in streams and ditches across the UK can be eaten but carries a risk of contamination by the larval stage of liver fluke (Fasciola hepatica), a parasitic flatworm whose lifecycle involves grazing livestock and aquatic snails. Liver fluke contamination cannot be detected by looking at the watercress and is not destroyed by washing. The risk is greatest in watercourses that run through or near fields grazed by sheep or cattle. The Food Standards Agency advises against eating raw wild watercress gathered from streams, and recommends cooking any foraged watercress thoroughly to kill any parasites. Watercress grown at home in clean water from the tap or a clean container carries no liver fluke risk and can be eaten raw. Commercially grown watercress in the UK is grown in controlled water systems and is safe to eat raw.