Why Are My Celery Leaves Curling?

Celery leaf miner

Celery leaf miner (Euleia heraclei) is the most common pest of celery and celeriac in UK gardens and also attacks parsnip, parsley, and other plants in the carrot family. The small fly lays eggs on the leaves and the larvae mine between the upper and lower leaf surfaces, creating pale, blistered, translucent patches that turn brown as the tissue dies. Leaves curl around the mined areas. There are two flight periods per year (May to June and July to August) and attacks can be severe, particularly in the second generation in late summer.

What to do

• Cover celery plants with fine insect mesh from transplanting through to harvest. This is the most effective preventive measure, as it excludes the adult fly from laying eggs on the leaves entirely.
• Remove and destroy mined leaves promptly, killing any larvae inside them by crushing the mined section between thumb and forefinger before removing the leaf.
• In uncovered crops, check plants weekly from May onward and remove affected leaves as soon as mining is noticed. Multiple applications of hand-removal are more practical than spraying for this pest.

Celery leaf spot

Celery leaf spot (Septoria apiicola) is a fungal disease that causes small, round, brown spots on celery leaves, stems, and stalks. In cool, wet conditions the spots enlarge and merge, causing yellowing and curling of the affected tissue and eventually the collapse of badly affected leaves. The disease spreads rapidly in humid, overcast conditions and is worst in wet summers. It is seed-borne, and outbreaks often start from infected bought transplants or seed.

What to do

• Use hot-water-treated seed if available, or buy seed from reputable UK suppliers: commercial celery seed is routinely treated to reduce seed-borne Septoria infection.
• Remove and destroy affected leaves as soon as spots appear, to reduce spore spread within the crop. Do not compost them.
• Avoid overhead watering and working among wet plants: the disease spreads via water splash and contact with contaminated surfaces.
• Copper-based fungicides (copper oxychloride) are approved for UK home garden use and provide some suppression of leaf spot when applied preventively in wet seasons.

Drought

Celery has the highest water requirement of almost any commonly grown UK vegetable: it evolved in marshy ground and requires consistently moist, never dry, soil throughout its growing season. Even brief drought causes the leaves to wilt, curl, and develop bitter flavours, and the stalks become stringy and hollow. Drought also triggers bolting (premature flowering), which makes the stalks inedible. In the UK, celery needs watering every few days in dry weather rather than the weekly watering schedule that suffices for most other vegetables.

What to do

• Water celery very frequently: every 2 to 4 days in warm, dry conditions. Celery grown in containers needs watering daily in summer. Never allow the soil to dry out.
• Incorporate large quantities of compost into the planting area before planting and apply a generous mulch around established plants to retain every possible drop of soil moisture.
• Plant celery in a position that receives afternoon shade in the hottest part of summer: east-facing or partially shaded positions dry out less rapidly than full-sun beds.

Aphids

Carrot-willow aphid (Cavariella aegopodii) and willow-carrot aphid both attack celery and related carrot family crops in the UK. They colonise the growing tips and underside of the youngest leaves, causing the young leaves to curl and distort as they develop. In heavy infestations the growing tip is completely distorted by aphid activity and the plant fails to develop further.

What to do

• Inspect celery growing tips weekly from May for aphid colonies. The aphids tend to be green to yellowish and may be difficult to see against the celery foliage.
• Apply insecticidal soap spray to infested growing tips, covering all surfaces thoroughly. Repeat every 5 to 7 days.
• Fine insect mesh over the crop from transplanting provides effective protection against both leaf miner and aphids simultaneously.

Bolting

Celery is a biennial that flowers in its second year after overwintering. In UK garden conditions, it can be tricked into bolting prematurely in its first summer if it experiences cold temperatures (below 10 degrees Celsius for an extended period) after the seedlings have established. Bolted celery plants produce a tall flower stem, the stalks become hollow and bitter, and the plant is essentially ruined for eating.

What to do

• Do not transplant celery outside before late May in most of the UK, and always harden off plants gradually over 2 weeks before transplanting to avoid sudden cold exposure.
• Use bolt-resistant varieties: self-blanching varieties such as 'Victoria', 'Loretta', and 'Tall Utah' are widely sold in UK seed catalogues with good bolt resistance.

Frequently asked questions

Why are my celery leaves curling?

Celery leaves curl most often from celery leaf miner damage, celery leaf spot, or drought. Celery leaf miner (Euleia heraclei) larvae mine into the leaf tissue, creating pale, blistered patches that cause the leaf to curl around the damage. Celery leaf spot (Septoria apiicola) produces small, brown spots on the leaves that merge in heavy infections, causing yellowing and curling of the affected tissue. Drought causes the leaves to wilt and curl, and is particularly damaging to celery, which has the highest water requirement of any commonly grown UK vegetable.

What is celery leaf miner and how do I control it?

Celery leaf miner (Euleia heraclei) is a fly whose larvae mine into the tissue of celery, celeriac, and parsnip leaves. The larvae feed between the upper and lower leaf surfaces, creating pale, blistered, translucent tunnels and patches that turn brown as the mined tissue dies. Leaves curl around the damaged areas. There are typically two generations per year in the UK: May to June and July to August. Control: remove and destroy mined leaves promptly, crushing any visible larvae inside them. Cover the crop with fine insect mesh from planting to harvest to prevent the adult fly from laying eggs. For established infestations in uncovered crops, remove affected leaves and the larvae inside them.

Why is my celery bolting?

Celery bolts (runs to seed) most often as a result of temperature stress, particularly exposure to cold temperatures (below 10 degrees Celsius) for an extended period after the seedlings have established. This cold exposure triggers the plant's vernalisation response and it flowers and sets seed prematurely rather than continuing to develop the edible stalks. Bolted celery becomes bitter and the stalks hollow out. Prevention: do not transplant celery outside before late May, as cold night temperatures in April and early May trigger bolting. Harden off seedlings gradually over 2 weeks before transplanting. Choose varieties selected for bolt resistance.

How do I grow celery in the UK?

Celery is one of the most demanding vegetables to grow in the UK, requiring consistent moisture, fertile soil, and protection from cold and drought throughout its long growing season. Sow in February to March under cover at 15 to 18 degrees Celsius; do not cover seeds as they need light to germinate. Prick out into individual modules when large enough to handle and grow on under cover until late May. Transplant to a well-prepared bed with plenty of incorporated compost, spacing plants 30 to 40 centimetres apart. Water very frequently: celery wilts and bolts in drought. Self-blanching varieties ('Victoria', 'Loretta') are easier than trench celery and do not require earthing up.