Why Are My Larkspur Leaves Curling?

Aphid infestation

Aphids are the most common pest on larkspur. They target the shoot tips and the undersides of the finely divided, feathery leaves, where their feeding causes the delicate foliage to curl, pucker, and distort. Green and black aphids are both common on consolida. On the tall, multi-stemmed plants, aphid colonies can be concentrated on the developing flower buds as well as the foliage, distorting the flower spikes. Heavy infestations significantly reduce the quality and length of the cut stems.

What to do

• Check the shoot tips and the undersides of young leaves regularly from late spring for aphid colonies.
• Knock aphids off with a strong jet of water early in the morning or spray with insecticidal soap every four to five days for two to three weeks.
• Avoid over-feeding with nitrogen-rich fertiliser, which produces soft, lush growth that is especially attractive to aphids.
• Encourage natural predators: the flowers of consolida attract hoverflies whose larvae feed on aphids.

Powdery mildew

Powdery mildew is a very common problem on larkspur, particularly as the season advances into warm, dry summer conditions. The feathery leaves develop a white powdery coating and the affected areas curl, pucker, and look bleached. Overcrowded plants where air circulation is poor are most susceptible. Mildew rarely kills larkspur outright, but it significantly affects the plant's appearance and shortens the productive cutting season by causing the foliage to deteriorate before the flower spikes are fully finished.

What to do

• Thin larkspur seedlings to at least 30 cm apart to improve air circulation. Overcrowded plants are far more susceptible than well-spaced ones.
• Remove and bin affected leaves and lower stems. Do not compost mildewed material.
• Spray remaining healthy growth with a sulphur-based fungicide or potassium bicarbonate solution every seven to ten days during susceptible periods.
• Ensure consistent watering: drought-stressed plants are significantly more vulnerable to powdery mildew.

Drought stress

Although larkspur is relatively tolerant of dry conditions once established, the finely divided leaves wilt and curl in hot, dry weather, particularly in containers or in free-draining sandy soils. Drought stress accelerates the plant's natural decline and shortens the flowering season. It also makes plants significantly more susceptible to powdery mildew, which can quickly follow a dry spell in summer.

What to do

• Water larkspur during prolonged dry spells, particularly from late May through June when the plants are at their most active.
• Mulch around plants to conserve soil moisture and keep the root zone cool.
• Avoid growing larkspur in containers: it performs far better in the open ground where it can access deep soil moisture.

Overwatering

Larkspur prefers well-drained soil and does not tolerate consistently waterlogged conditions. In heavy clay or in persistently wet ground, the roots deteriorate and the plant declines: the leaves yellow and curl even when the soil is wet, and the stems may become soft and weak. Waterlogging is most likely during a wet spring, particularly for autumn-sown plants that have been sitting in cold, wet soil over winter.

What to do

• Plant larkspur in well-drained, even fairly poor soil. Heavy, waterlogged ground produces weak plants prone to disease.
• On clay soils, improve drainage by incorporating grit and organic matter before sowing.
• Avoid watering during wet periods. Larkspur does not need additional water during a typical wet UK spring.

Cold damage

Larkspur is a hardy annual and will withstand normal UK winters without damage once established as a small rosette from an autumn sowing. However, late hard frosts in March or April can damage the emerging flower stems and tender new growth of autumn-sown plants, causing the shoot tips to curl, blacken, and collapse. Severe late frosts may kill the flower buds, resulting in a poor flowering display despite the plant otherwise appearing healthy at the base.

What to do

• Cover autumn-sown larkspur with a single layer of horticultural fleece during late hard frost events in spring.
• Damaged shoot tips can be cut back cleanly: the plant will often produce new lateral shoots below the damaged section.
• Spring-sown larkspur sown in March or April avoids the risk of late spring frost damage to the developing shoots.

Frequently asked questions

Why are my larkspur leaves curling?

Larkspur leaves curl most often from aphid infestation or powdery mildew. Aphids colonise the shoot tips and the undersides of the finely divided leaves, causing distortion and curling. Powdery mildew causes the feathery foliage to develop a white coating and curl, particularly in warm, dry conditions later in the season.

When should I sow larkspur?

Larkspur germinates best in cool conditions and is ideally sown direct in autumn for the best early-summer display, or in early spring from February to April. It dislikes root disturbance and should be sown direct in its final growing position. Autumn-sown plants produce the tallest, most vigorous flowers.

Why is my larkspur not flowering?

Larkspur flowers best in cool conditions and may be slow to flower if sown too late in spring or in a warm, sheltered position. It also needs full sun and well-drained soil to perform well. Plants sown in rich, fertile soil sometimes produce vigorous foliage but fewer flowers. In very hot summers, larkspur may decline before reaching full flowering potential.

Is larkspur poisonous?

Yes, all parts of larkspur and consolida are toxic if ingested, particularly the seeds and young growing tips. The plant contains alkaloids that can cause serious poisoning in humans and livestock. Wear gloves when handling consolida and wash hands after working with the plants. Keep children and pets away from the plants in the garden.