Why Are My Foxglove Leaves Curling?

Powdery mildew

Erysiphe digitalis is the most commonly encountered disease of foxgloves in UK gardens. White, powdery, talc-like coating develops on the upper surfaces of leaves; affected leaves curl, pucker, and develop white patches that can spread to cover large leaf areas. Most prevalent in dry, warm weather with poor air circulation from July to September. Strongly associated with drought stress at the root level combined with warm dry weather.

What to do

• Maintain consistent root moisture with a thick mulch (7 to 10 cm) of leaf mould or composted bark applied in spring before the soil dries; water deeply at the base of the plant during dry periods from June to September (not overhead); improve air circulation by not planting too closely and by removing yellowing lower leaves; grow in a partially shaded, moisture-retentive, woodland-edge position; sulphur-based fungicide sprays are approved in the UK for powdery mildew on ornamental plants and can be applied preventatively from the first signs of mildew.

Drought stress

The large, soft, hairy leaves of Digitalis purpurea are relatively thin and wilt very dramatically and quickly when the soil dries in hot UK summer weather; midday wilting in a hot, exposed position is largely a temporary protective response and the leaves typically recover in the evening. Severe, prolonged drought can cause permanent wilting, leaf yellowing, and premature death of the rosette leaves.

What to do

• Grow in a moisture-retentive, humus-rich, partially shaded position enriched with large quantities of well-rotted compost or leaf mould; apply a deep mulch in spring; water deeply and regularly in hot dry periods; foxgloves grow most successfully in a woodland-edge or dappled-shade position where soil moisture and shelter from the hottest summer afternoon sun naturally reduce drought stress.

Aphid infestations

Aphids attack the developing shoot tips and developing flower spikes; feeding causes young leaves and bracts at the shoot tip to curl and distort. Grey-green or black aphid colonies are visible on shoot tips, on the undersides of distorted leaves, and clustered between the developing flower buds on the lower part of the flower spike. Heavy infestations can reduce flowering quality on the developing spike.

What to do

• Squash aphid colonies on the shoot tip by hand, or knock off with a jet of water; tolerate for a few days initially to allow natural predators (ladybirds, lacewing larvae, parasitic wasps) to colonise; check developing flower spikes from April to June and remove aphids by hand before they build up to damaging levels; apply insecticidal soap or pyrethrin spray if needed, targeting the colonies directly.

Natural biennial senescence

Digitalis purpurea is a biennial: first year develops a rosette of large leaves; second year produces the tall flower spike, sets seed, then dies. As the flower spike extends rapidly in spring, the lower, older rosette leaves naturally yellow, wilt, and die back from the base upward; this is entirely normal as the plant redirects all energy into flowering and seed production. This yellowing and dying back of lower leaves does not indicate disease or stress.

What to do

• No action needed for normal biennial leaf senescence. Remove the yellowing lower leaves for tidiness if desired. Allow some flower spikes to set and drop seed before cutting them off to ensure a self-seeding colony of new first-year rosettes for the following year. True perennial foxgloves such as Digitalis grandiflora or D. x mertonensis are alternatives if a longer-lived plant is preferred.

Frequently asked questions

Why are my foxglove leaves curling?

Foxglove leaves curl most commonly because of powdery mildew (Erysiphe digitalis; white powdery talc-like coating on upper leaf surfaces; leaves curl and pucker; most prevalent in dry warm weather with poor air circulation July to September; strongly associated with drought stress at root level; thick mulch; deep watering at base; partially shaded moisture-retentive woodland-edge position; sulphur-based fungicide approved for UK ornamental plants), drought stress (large soft hairy leaves wilt very dramatically and quickly in hot summer weather; midday wilting largely a temporary protective response; severe prolonged drought causes permanent wilting and premature leaf death; moisture-retentive humus-rich partially shaded position; deep mulch; water deeply in hot dry periods), aphid infestations on developing shoot tips (grey-green or black aphid colonies on shoot tips and developing flower spikes; squash by hand or knock off with water jet; tolerate briefly for natural predators; insecticidal soap or pyrethrin spray if needed), or natural biennial senescence (D. purpurea is biennial; lower rosette leaves naturally yellow and die back as flower spike extends in second year; entirely normal; allow some spikes to set seed for self-seeding colony; consider true perennial species like D. grandiflora for longer-lived plants).

Is foxglove biennial or perennial?

Digitalis purpurea (common foxglove, native UK species): biennial in most garden behaviour; first year develops rosette of large soft hairy leaves without flowering; second year produces tall (1 to 1.8 m) flower spike covered in tubular purple pink white or cream spotted flowers; sets seed; then typically dies; some individuals may produce a second smaller spike in year 3; self-seeds prolifically in suitable conditions (open disturbed acid to neutral humus-rich soil in partial shade); colony appears perennial in the garden even though individual plants are biennial; let some spikes set seed to ensure continuous self-seeding colony. D. grandiflora (yellow foxglove): true perennial; forms increasingly large clump over time; creamy yellow smaller flowers on shorter spikes (60 to 90 cm). D. lutea (straw foxglove): true perennial; small neat narrow leaves; very small pale creamy-yellow flowers; more drought-tolerant than D. purpurea. D. x mertonensis (strawberry foxglove): sterile true-perennial hybrid; large copper-pink flowers; most perennial-behaving of the pink-flowered foxgloves available in the UK.

How do I prevent powdery mildew on foxgloves?

Soil moisture: moisture-retentive humus-rich woodland-edge or partially shaded soil that does not dry out rapidly in summer; large quantities of well-rotted garden compost or leaf mould at planting; thick mulch (7 to 10 cm) of leaf mould or composted bark applied in spring. Watering: water deeply and regularly during dry periods June to September at the base of the plant (not overhead); deep watering reaching root zone more effective than shallow frequent surface watering. Air circulation: good air movement around plants reduces still warm humid leaf-surface conditions favouring mildew; avoid planting too closely; avoid very enclosed sheltered spots; remove old yellowing lower leaves. Position: partial shade (dappled shade under deciduous trees or morning sun with afternoon shade); avoid full hot afternoon sun in July and August which creates ideal mildew conditions on large soft leaves combined with dry soil. Chemical: sulphur-based fungicide sprays approved in the UK for powdery mildew on ornamental plants; primarily preventative; remove badly mildewed leaves before spraying.

Are foxgloves poisonous?

Yes. All parts of all Digitalis species are toxic to humans, pets, and livestock including the leaves, flowers, seeds, and roots. Toxicity is due to cardiac glycosides (primarily digitoxin and digoxin) that affect heart function; present throughout the plant; not destroyed by drying or cooking. Symptoms of foxglove poisoning include nausea, vomiting, diarrhoea, abdominal pain, confusion, visual disturbances (particularly yellow vision or seeing halos around lights associated with digitalis toxicity), and potentially serious heart arrhythmias and cardiovascular effects at higher doses. In the garden: generally safe to grow with appropriate care and awareness; wash hands after handling; keep children and pets away from the plant; do not allow children to handle or taste any part of the plant; wear gloves when handling if sensitive to contact skin irritation from the hairy leaves. If poisoning suspected: contact NHS emergency services (999 in the UK) or NHS 111 for general poisoning queries from members of the public. Medicinal use: the cardiac glycosides extracted from Digitalis lanata and D. purpurea are the source of the prescription heart medicines digoxin and digitoxin; this does not make any part of the garden plant safe to consume.