Why Are My Parsley Leaves Curling?

Aphid infestations

The most commonly encountered pest of parsley in UK gardens. The willow-carrot aphid, celery aphid, and other species attack young shoot tips and establish colonies between the tightly curled leaves of curly-leaved parsley where they are difficult to see. Feeding causes leaves to curl, pucker, and distort; sticky honeydew deposits and sooty mould on the leaves; ants attending the colonies are a diagnostic sign.

What to do

• Gently uncurl the tight curled leaves of curly-leaved parsley to expose concealed aphid colonies; squash or rub off colonies with damp fingers, or knock off with a medium-pressure jet of water; tolerate small infestations for several days to allow natural predators (ladybirds, lacewing larvae, parasitic wasps) to establish; for culinary parsley, hand control is strongly preferred over insecticide sprays; if spray is used, check the edible crop withholding period on the product label (typically 24 to 48 hours).

Carrot fly damage

Psila rosae (carrot fly) larvae burrow into the taproot of parsley creating characteristic brown, slimy, rusty-brown tunnels; the root damage disrupts water and nutrient uptake; above-ground symptoms are progressive yellowing and wilting that collapses without obvious cause. Lifting a suspected carrot-fly-damaged plant reveals the tunnelling damage in the root. Two main egg-laying flights per year: May to June and July to August.

What to do

• Surround the growing bed with fine insect-proof mesh (maximum 0.8 mm aperture) on a frame at least 60 to 90 cm tall; the adult carrot fly flies close to the ground below about 60 cm, so a correctly installed barrier prevents it from reaching the plants; grow parsley in containers raised above about 60 cm (balcony, patio, raised pot) as a practical alternative; sow early (March to April under cover) to establish a good root before the May to June flight; minimise foliage bruising when harvesting as the volatile compounds released attract the female fly.

Crown rot and overwatering

Parsley has a fleshy, carrot-like taproot and a dense crown at the base; the crown is susceptible to rotting in persistently wet, poorly draining, cool conditions. Symptoms begin as progressive yellowing and wilting of the outer leaves from the base; the plant progressively collapses; the crown tissue is brown and soft at the base. Associated with waterlogged, heavy soils and very wet UK autumn and winter conditions.

What to do

• Improve drainage by incorporating coarse grit into heavy UK clay soils; or grow in raised beds or containers; ensure containers have large drainage holes and do not sit in constantly filled saucers; water parsley moderately and allow the soil surface to begin to dry between waterings; in containers, use a free-draining, moisture-retentive multipurpose compost rather than a compacted, poorly draining compost; in very wet UK autumn and winter conditions, covering parsley with a cloche or growing undercover significantly reduces crown rot risk.

Natural second-year bolting

Parsley is a biennial; in its second year it diverts energy from leaf production to a rapidly elongating flower stalk from about March onward in UK conditions. Leaf quality deteriorates significantly; the leaves produced after bolting begins are smaller, fewer, and less flavourful than first-year leaves. This is entirely natural and expected behaviour.

What to do

• Replace parsley plants after their first full year of production with fresh young first-year plants; for continuous supply, maintain both a first-year planting for best leaf quality and a second-year planting for early spring leaves before it bolts; allow some second-year plants to set seed for a self-seeding colony; fresh plants can also be bought as plugs or small pots from a UK nursery or garden centre in spring to avoid the slow germination of parsley seed.

Frequently asked questions

Why are my parsley leaves curling?

Parsley leaves curl most commonly because of aphid infestations (most commonly encountered pest of parsley in UK gardens; willow-carrot aphid celery aphid and other species attack young shoot tips and establish colonies between tightly curled leaves of curly-leaved parsley; feeding causes leaves to curl pucker and distort; sticky honeydew deposits and sooty mould; ants attending colonies are a diagnostic sign; gently uncurl leaves to expose colonies; squash or rub off by hand or knock off with water jet; tolerate briefly for natural predators; insecticidal soap if needed; hand control preferred for culinary parsley), carrot fly damage (Psila rosae larvae burrow into taproot creating brown slimy rusty-brown tunnels; progressive yellowing and wilting; lift plant and examine taproot to confirm; fine insect-proof mesh barrier 60 to 90 cm tall; grow in containers raised above 60 cm; sow early March to April to establish root before May to June flight; minimise foliage bruising when harvesting), crown rot and overwatering (fleshy taproot and dense crown susceptible to rotting in persistently wet poorly draining cool conditions; progressive yellowing and wilting from base; brown soft crown tissue; improve drainage; raised beds or containers; free-draining compost; moderate watering; cloche or undercover growing in very wet autumn and winter), or natural second-year bolting (biennial; second year diverts energy to rapidly elongating flower stalk from about March; leaf quality deteriorates; entirely natural; replace with fresh first-year plants after first full year of production).

How do I deal with aphids on parsley?

Identifying aphids on parsley: small soft-bodied yellow-green pale green grey-green or black aphids on young shoot tips developing central leaves and between curled leaves of curly-leaved parsley; sticky shiny honeydew deposits; sooty mould on honeydew deposits; ants running up and down the plant; yellow distorted or puckered young leaves at shoot tip. Control: hand removal and water jet: gently uncurl curled leaves to expose concealed colonies; squash or rub off with damp fingers; medium-pressure jet of water to knock aphids off; repeat regularly; tolerance and natural predation: tolerate small infestations for several days for natural predators (ladybirds lacewing larvae parasitic wasps) to establish; avoid insecticide use that kills natural predators; chemical control: insecticidal soap or pyrethrin-based contact insecticide spray; direct at aphid colonies; check edible crop withholding period on product label (typically 24 to 48 hours); hand control generally preferred for culinary herb to avoid residue risk.

How do I protect parsley from carrot fly?

Understanding the carrot fly: small shiny black fly with orange-yellow head and legs; female detects host plants by smell of volatile compounds released when leaves are bruised or handled; lays batches of small white eggs in soil near base of susceptible plants; cream legless 6 to 9 mm larvae burrow into tap and side roots creating brown slimy rusty-brown tunnelling damage; two main UK egg-laying flights (May to June and July to August); possible third partial generation in mild UK autumns. Physical barriers: most reliable and most widely used method; fine insect-proof mesh (maximum 0.8 mm aperture) on a frame to a height of 60 to 90 cm; ensure barrier pulled down to ground with no gaps; adult female flies close to ground below about 60 cm. Growing in raised containers: containers on a balcony patio or raised surface above about 60 cm naturally protected; practical alternative to netting for small quantities. Timing of sowing: sowing very early (March to April under cover) gives a crop well-established before May to June flight; crops sown during main carrot fly flight periods most at risk; sowing very late (August to September) gives a crop that establishes between the two main flights. Avoiding bruising foliage: harvest leaves early in the morning before the day warms up; harvest from different plants on each occasion; thin in the morning and remove thinnings promptly.

Is parsley biennial and when does it bolt?

Yes, parsley is biennial. First-year behaviour (Year 1): germinates from seed; develops rosette of culinary leaves and substantial fleshy carrot-like taproot; does not flower in first year in most UK conditions; best-quality most productive most culinary-useful leaves; very slow to germinate from seed (typically 3 to 6 weeks; soak seed overnight in warm water before sowing; sow in warm compost at approximately 18°C; pot-raised transplants from nursery or garden centre avoid germination problem but root disturbance can be a concern). Second-year behaviour (Year 2): from about March onward the plant begins to divert energy from leaf production to development of a rapidly elongating flower stalk; flowering stem extends quickly producing umbels of small white or cream flowers; seed sets in summer; plant then dies; leaf quality deteriorates significantly once bolting begins; leaves produced after bolting are smaller fewer and less flavourful. What to do: replace parsley plants after first full year of production; for continuous supply maintain both a first-year planting for best leaf quality and a second-year planting for early spring leaves; allow some plants to set seed for a self-seeding colony.