Why Are My Cerinthe Leaves Curling?

Aphid infestation

Aphids are the most common pest problem on cerinthe. They are particularly drawn to the tender shoot tips and the bracts that wrap around the tubular flower clusters, where the sheltered, soft tissue makes ideal feeding and colonising territory. The bracts naturally have a curled, wrapping habit, and aphid colonisation within these structures intensifies the curling effect while also distorting the adjacent leaves. Green and blackfly are both common on cerinthe. Heavily infested plants produce fewer flowers and the characteristic silvery-blue colouring of the bracts becomes dull and distorted.

What to do

• Part the bracts and inspect the sheltered areas around the flower clusters for aphid colonies.
• Knock aphids off with a jet of water directed into the bracts and at the undersides of leaves.
• Spray with insecticidal soap every four to five days for two to three weeks, ensuring coverage within the bract clusters where colonies shelter.
• The tubular flowers are important for bumblebees, so spray in the evening when bee activity is minimal.

Cold damage

Cerinthe is substantially more cold-tolerant than many half-hardy annuals but is not fully hardy, and hard frost causes significant damage to the thick, succulent-like leaves. When exposed to temperatures below minus 3 to minus 5 degrees Celsius, the leaves become waterlogged and translucent, then collapse and turn black or brown. Milder cold snaps cause the leaf edges to curl and develop pale, discoloured areas. Overwintered outdoor plants are most at risk during sudden cold spells in January and February after a mild autumn has kept them in growth.

What to do

• In cold regions, overwinter cerinthe in a cold greenhouse, cold frame, or sheltered porch rather than outdoors.
• In milder areas, a double layer of horticultural fleece provides enough protection through most UK winters.
• After a cold spell, remove and cut back damaged leaves and shoots. Cerinthe often regrows from healthy tissue at the base once temperatures improve.
• Do not plant cerinthe out in spring until the risk of hard frost has passed and nighttime temperatures are reliably above 2 to 3 degrees Celsius.

Drought stress

Despite its slightly succulent appearance, cerinthe is not a true drought-tolerant plant and needs consistent moisture to perform well. In dry conditions, particularly in containers or in free-draining soils during a dry spring, the thick leaves lose their firm, upright posture, curl slightly, and the plant's vivid blue-green colouring becomes duller. The flowers also become shorter-lived in drought conditions.

What to do

• Water cerinthe when the top 2 to 3 cm of soil feel dry. Keep soil consistently moist during the main growing and flowering period.
• Mulch around border plants to retain soil moisture during dry spells.
• Container-grown cerinthe needs more frequent watering: check daily in warm weather and water before the leaves show stress symptoms.

Overwatering

Cerinthe's slightly succulent leaves store some moisture, and the plant is susceptible to root rot in persistently waterlogged compost or heavy, poorly draining soil. Overwatered cerinthe develops yellowing, curling leaves, loses its characteristic vibrant colouring, and the stems may become soft and sappy at the base. This is most common in autumn-sown plants growing through a wet UK winter or in containers watered on a fixed schedule without regard to actual soil moisture.

What to do

• Plant cerinthe in well-drained soil. In containers, use a free-draining compost and ensure adequate drainage holes.
• Reduce watering significantly during cool, wet, or overcast periods, particularly for overwintering plants in cold frames or greenhouses.
• If root rot is suspected, remove the plant from its pot, trim away mushy roots, and replant in fresh, well-aerated compost.

Powdery mildew

Powdery mildew occasionally affects cerinthe as the season advances and conditions become warmer and drier, or when plants are overcrowded in sheltered positions. The thick leaves develop a white powdery coating, and the affected areas curl and distort. It is less common on cerinthe than on many other garden plants and usually appears only on plants that are already stressed or nearing the end of their natural season.

What to do

• Improve air circulation around plants and avoid growing them too densely.
• Remove and bin affected leaves. Spray remaining healthy growth with a sulphur-based fungicide or potassium bicarbonate solution.
• Ensure adequate watering: plants under drought stress are significantly more susceptible to powdery mildew than well-watered plants.

Frequently asked questions

Why are my cerinthe leaves curling?

Cerinthe leaves curl most often from aphid infestation or cold damage. Aphids particularly target the shoot tips and the bracts surrounding the tubular flowers, causing them to curl. Cold snaps in early spring or late autumn can cause the thick, succulent-like leaves to become waterlogged and curl or collapse.

Why are cerinthe leaves spotted and curling?

White or pale spots on cerinthe leaves are usually the natural white speckling that many cultivars, particularly Cerinthe major Purpurascens, display on their foliage. This is an ornamental feature, not a sign of disease. If the spots appear alongside curling and distortion, check for aphid damage or powdery mildew.

When should I sow cerinthe?

Cerinthe is best sown in autumn for overwintering and early spring flowering, or in late winter under glass for planting out in spring. It germinates readily at cool temperatures. Autumn-sown plants that overwinter successfully are more robust and flower earlier than spring-sown plants.

Is cerinthe hardy in the UK?

Cerinthe major is half-hardy and will not survive hard frosts, but it is more cold-tolerant than many half-hardy annuals and can overwinter successfully in milder UK gardens, particularly in sheltered positions or in the south and west. A cold but frost-free greenhouse or cold frame provides reliable overwintering protection.