Why Are My Ammi Leaves Curling?

Aphid infestation

Aphids are the most common pest problem on ammi. As a member of the carrot family, ammi is attractive to several aphid species including the willow-carrot aphid and various green aphid species that move onto umbellifer plants in late spring and summer. They colonise the shoot tips and the undersides of the feathery leaves, causing the fine foliage to curl and distort around the colonies. On tall ammi plants, infestations on the upper portions of the plant can be difficult to spot until the damage is visible from below.

What to do

• Check the shoot tips and the undersides of curling leaves for aphid colonies, particularly from late spring onwards when migratory aphids move onto their summer host plants.
• Knock aphids off with a jet of water. The tall stems of ammi make this easier than on low-growing plants.
• Spray with insecticidal soap every four to five days for two to three weeks for persistent infestations. Spray in the evening to avoid harming visiting pollinators.
• The flowers of ammi are excellent habitats for beneficial insects including parasitic wasps and hoverflies that naturally control aphid populations.

Drought stress

Despite being a reasonably robust annual, ammi has fine, feathery leaves that lose moisture relatively quickly in warm, sunny conditions. During a dry spell, particularly when plants are approaching their flowering stage and making rapid upward growth, the leaves wilt and curl in the afternoon heat. Young transplants and recently established seedlings are most vulnerable. Drought stress at the wrong time can cause the plant to bolt prematurely without developing to its full potential height and flower size.

What to do

• Keep the soil consistently moist during dry periods, particularly for young plants and those putting on rapid growth before flowering.
• Water in the morning so the soil stays moist through the warmest part of the day.
• A 5 cm mulch of garden compost around established plants helps significantly with moisture retention and also suppresses competing weeds around the base of the stems.
• Container-grown ammi needs more frequent watering than border plants. Check the compost daily in warm weather and water before the leaves show drought symptoms.

Overwatering

Ammi prefers well-drained soil and suffers in persistently waterlogged conditions. In heavy clay soils or after prolonged wet weather, the roots can rot and the plant begins to decline: the lower leaves yellow and curl, and the plant fails to reach its full height before deteriorating. This is more common in very wet UK springs or in containers without adequate drainage.

What to do

• Plant ammi in well-drained, reasonably fertile soil. Improving clay soil with grit and organic matter before sowing helps drainage significantly.
• In containers, ensure excellent drainage. Ammi is quite tall for a container plant and does best in large, well-drained pots rather than small ones.
• Reduce watering frequency during prolonged wet or cool periods.

Carrot fly

Carrot fly (Psila rosae) may occasionally attack ammi, as it is in the same plant family as carrots and parsnips. The tiny larvae tunnel into the roots and stems near soil level, causing the plant to wilt, yellow, and collapse without obvious above-ground cause. The feathery foliage curls as the plant loses its ability to take up water. Unlike aphid damage, there is no visible pest on the above-ground parts of the plant; the damage is below soil level.

What to do

• Cover young ammi plants with fine insect-proof mesh to prevent the adult flies from laying eggs at the base of the plants. The mesh needs to be in place from germination or transplanting.
• Avoid sowing or planting ammi immediately after carrots, parsnips, or other Apiaceae in the same spot, as carrot fly populations in the soil will be elevated.
• There is no effective chemical treatment once larvae are in the roots. Remove affected plants and improve the growing conditions for any remaining healthy plants.

Powdery mildew

Powdery mildew occasionally affects ammi as the season progresses, causing a white powdery coating on the stems and leaves alongside some curling and distortion. It is most common on plants in very sheltered positions with poor air circulation, particularly in warm, dry summers. By the time powdery mildew appears on ammi, the plant is usually well into its flowering period and the impact on the overall display is limited.

What to do

• Thin overcrowded plants to improve air circulation around the stems.
• Remove and bin affected material. Spray remaining healthy growth with a sulphur-based fungicide if the infection is extensive.

Frequently asked questions

Why are my ammi leaves curling?

Ammi leaves curl most often from aphid infestation or drought stress. As a member of the carrot family, ammi is attractive to aphids which colonise the shoot tips and the undersides of the feathery leaves, causing them to curl and distort. Drought causes the fine leaves to wilt and curl rapidly in warm weather.

Why are my ammi majus leaves curling and going yellow?

Yellow curling leaves on ammi can indicate waterlogged roots, nutrient deficiency in very poor soil, or the natural ageing of lower leaves as the plant matures and puts energy into flower production. If yellowing affects the whole plant and the compost is wet, root rot from overwatering is the likely cause.

Can ammi cause skin irritation?

Yes. Ammi majus (bishop's flower) contains furanocoumarins that can cause phototoxic reactions: contact with the sap followed by sun exposure can cause burns and blistering on sensitive skin. Wear gloves and long sleeves when handling ammi, particularly in bright sunshine.

When should I sow ammi?

For the best results, sow ammi in autumn for spring germination and early summer flowering. It can also be sown in early spring under glass for planting out after the last frost, or direct-sown outdoors from April. Ammi majus is a half-hardy annual; Ammi visnaga (toothpick plant) behaves similarly.