Why Are My Salpiglossis Leaves Curling?

Aphid infestation

Aphids are the most common pest on salpiglossis. The sticky, glandular hairs on the stems and leaves trap small insects naturally, but aphids colonise the soft shoot tips and the undersides of the lobed leaves with particular persistence. Green peach aphid and Myzus persicae are frequently found on salpiglossis. Aphid feeding causes the soft leaves to curl, pucker, and develop a distorted, crinkled appearance. Heavy infestations on young plants stall growth significantly and can prevent or delay flowering. Because salpiglossis is already slow to establish in UK conditions, aphid pressure in the early weeks after planting out is especially damaging.

What to do

• Check the shoot tips and the undersides of the lobed leaves regularly from early summer. The sticky hairs make aphid colonies harder to spot than on smooth-leaved plants.
• Spray with insecticidal soap every four to five days for two to three weeks, ensuring thorough coverage of the sticky, hairy leaf surfaces.
• A jet of water can help, though the sticky stems mean aphids are less easily dislodged than on smoother plants.
• Avoid high-nitrogen feeding which produces the soft, lush growth that aphids find most attractive.

Cold stress

Cold stress is the most common reason salpiglossis fails in UK gardens. As a half-hardy annual from the Andes, salpiglossis needs consistent warmth to grow and flower well. Temperatures below 10 degrees Celsius at night cause the soft, lobed leaves to curl, pale, and the plant to stall entirely. Plants that have experienced cold stress often take several weeks to recover properly once temperatures improve. In a cold or wet UK summer, salpiglossis under glass in a cold frame, polytunnel, or greenhouse consistently outperforms outdoor plants in exposed positions.

What to do

• Do not plant salpiglossis outdoors until nighttime temperatures are reliably above 10 degrees Celsius, typically late May to early June in most UK locations.
• Harden off thoroughly for at least two weeks before planting out: salpiglossis is particularly sensitive to the sudden transition from protected growing conditions.
• Choose the warmest, most sheltered, sunniest position available. South or south-west facing beds in front of a wall are ideal.
• Cover with fleece on unexpectedly cold nights in early summer. Cold-stressed plants that have not yet flowered may not have time to recover before the season ends.

Overwatering

Salpiglossis prefers well-drained soil and does not tolerate persistently wet conditions. In heavy clay, in containers without adequate drainage, or during a wet UK summer, the fine root system deteriorates and the plant declines. The soft leaves yellow and curl, and the plant may collapse at the stem base. Overwatering is most likely when plants are maintained on a fixed watering schedule during cool, overcast periods when the compost dries very slowly.

What to do

• Plant salpiglossis in well-drained, fertile but not overly rich soil. Good drainage is more important than high fertility.
• In containers, use a free-draining compost blended with perlite and ensure excellent drainage holes.
• Allow the surface of the compost to dry slightly between waterings. Do not water on a schedule: check the compost moisture before watering.
• Reduce watering frequency during cool, overcast periods when evaporation from the compost is minimal.

Drought stress

Salpiglossis needs consistent moisture to grow and flower well, particularly during the main flowering period from midsummer onwards. Container plants and those in very free-draining soil in a warm, sunny position are most at risk. The soft leaves curl and wilt rapidly when the compost dries out, and drought stress causes the flowers to drop prematurely and the flower buds to fail to open fully. Unlike some annuals, salpiglossis does not recover well from repeated drought cycles.

What to do

• Water salpiglossis regularly during warm, dry periods, particularly from midsummer onwards during the main flowering season.
• Container-grown plants need watering every one to two days in warm weather. Check the compost daily and water before the leaves show stress.
• Mulch around border plants to retain soil moisture, which is particularly important in a dry summer.

Powdery mildew

Powdery mildew occasionally affects salpiglossis later in the season, particularly in warm, dry conditions or when plants are crowded together. The lobed leaves develop a white powdery coating and curl at the margins. It is most common on plants that have been drought-stressed or that are growing in positions with poor air circulation.

What to do

• Space salpiglossis plants at 30 to 45 cm to ensure adequate air circulation between the branching stems.
• Remove affected leaves and spray healthy growth with a sulphur-based fungicide at the first signs of powdery mildew.
• Ensure consistent watering: drought-stressed plants are significantly more susceptible to powdery mildew than well-watered ones.

Frequently asked questions

Why are my salpiglossis leaves curling?

Salpiglossis leaves curl most often from aphid infestation or cold stress. Aphids cluster on the sticky, hairy shoot tips and the undersides of the lobed leaves, causing them to curl and distort. Cold nights below 10 degrees Celsius cause the soft leaves to curl and the plant to stall, as salpiglossis is a half-hardy annual that needs sustained warmth to grow and flower well.

Why is my salpiglossis not flowering?

Salpiglossis that fails to flower is most often suffering from insufficient warmth, too much nitrogen, or having been planted out before nighttime temperatures were reliably above 10 degrees Celsius. Rich, recently manured soil encourages lush leaf growth at the expense of flowers. Move containers to the warmest available position and switch to a high-potash feed to encourage flowering.

When should I sow salpiglossis?

Sow salpiglossis under glass from February to April at 18 to 20 degrees Celsius. Do not cover the seed, as it needs light to germinate. Prick out carefully as salpiglossis resents root disturbance. Harden off thoroughly for two weeks before planting outside in late May or early June after the last frost.

Does salpiglossis need staking?

Yes, taller varieties of salpiglossis need staking, particularly in exposed positions. The slender, branching stems can reach 60 to 90 cm and are susceptible to wind damage. Insert canes or twiggy sticks at planting time and tie in loosely as the plants grow. Shorter compact varieties may not need support in a sheltered position.