Why Are My Pak Choi Leaves Curling?

Flea beetle

Flea beetles (Phyllotreta species) are the single most damaging pest of pak choi in UK gardens. The tiny, jumping beetles chew small, round holes in the leaves from the moment the seedlings emerge, and in dry, warm conditions they can completely skeletonise young pak choi plants within days. The thin, soft leaves of pak choi are especially vulnerable compared to the thicker leaves of cabbage or kale. Established plants with well-formed heads are more tolerant than seedlings, but flea beetles attack pak choi at all stages. There is no practical chemical alternative to insect mesh for controlling flea beetles on pak choi.

What to do

• Cover pak choi sowings with fine insect mesh immediately at sowing, before the seedlings emerge, and keep it in place until harvest. This is not optional: without mesh, flea beetle damage on pak choi is almost certain in any UK garden from April through September.
• Water the soil around the plants consistently: flea beetles are most damaging on dry, stressed plants and are significantly less active on well-watered plants growing in moist soil.
• Sow pak choi in late July and August for autumn harvest: flea beetle populations decline sharply as temperatures drop in September, making late-summer sowings much easier to protect than spring sowings.

Cabbage aphid

Cabbage aphid (Brevicoryne brassicae) colonises pak choi plants in spring and summer, forming dense, grey-green colonies on the underside of leaves and in the heart of the developing head. The leaves curl inward around the colonies and the growing tip may be completely distorted in heavy infestations. Aphids on pak choi may be less visible than on other brassicas because they are hidden within the tightly packed leaves.

What to do

• Check the underside of pak choi leaves and inside the developing head weekly for aphid colonies. Small colonies can be squashed by hand. Apply insecticidal soap spray to larger infestations, covering all leaf surfaces including inside the heart of the plant.
• Insect mesh that keeps off flea beetles also provides effective aphid protection: a single physical barrier covers both pests.

Caterpillars

Large and small cabbage white caterpillars (Pieris brassicae and Pieris rapae) attack pak choi, rasping large holes in the outer leaves and working toward the heart of the plant. The leaves curl around damaged areas. The fast growth of pak choi means caterpillar damage can reach the edible heart very quickly, particularly from larger Pieris brassicae caterpillars feeding in groups.

What to do

• Inspect pak choi plants weekly for eggs (yellow clusters on the underside of leaves) and caterpillars. Remove both by hand. Fine insect mesh is the most reliable prevention.

Downy mildew

Downy mildew (Hyaloperonospora parasitica) produces pale yellow patches on pak choi leaves with a white-grey downy growth beneath. In cool, wet conditions the leaves yellow and curl rapidly. Pak choi grown under cover in autumn and winter is particularly susceptible to downy mildew in damp, poorly ventilated conditions.

What to do

• Space pak choi at the correct distances (20 to 30 centimetres for full heads; closer for baby leaf). Remove and destroy affected outer leaves promptly.
• Ventilate covered growing areas thoroughly: downy mildew on pak choi under glass or polytunnel is almost entirely a ventilation problem.

Bolting

Pak choi bolts (runs to flower) very easily in response to cold temperatures, long days, or drought. Spring sowings in April and May are the most prone: the long days and cold nights of spring trigger bolting before the plant has time to form a useful head. Once pak choi bolts, the head opens and the leaves become tough and bitter.

What to do

• Sow pak choi in late July to mid-August for autumn harvest rather than in spring: late-summer sowings develop in naturally shortening days and are far less prone to bolting.
• Sow direct rather than transplanting where possible: root disturbance from transplanting can trigger bolting even in correctly timed sowings.
• Choose bolt-resistant varieties such as 'Joi Choi', 'Canton White', or 'Green Revolution' for spring sowings if you cannot avoid them.

Frequently asked questions

Why are my pak choi leaves curling?

Pak choi leaves curl most often from flea beetle damage or cabbage aphid infestation. Flea beetles (Phyllotreta species) chew numerous small holes in pak choi leaves and the tissue between the holes curls and dies in heavy attacks. Cabbage aphid (Brevicoryne brassicae) colonises the underside of leaves and causes them to curl inward around the feeding colonies. Pak choi is one of the brassicas most severely damaged by flea beetles in UK gardens: its thin, soft leaves are easily shredded by beetle feeding, and without protection the plants can be completely destroyed before they reach a useful harvest size.

Why is my pak choi bolting?

Pak choi bolts (runs to flower) very readily when it experiences stress, particularly exposure to cold temperatures after sowing, drought, or root disturbance from transplanting. Spring sowings of pak choi are particularly prone to bolting: the long days and fluctuating temperatures of April and May trigger flowering before the plant has time to develop a useful head. The best seasons for pak choi in the UK are late summer (sown July to August, harvested September to October) and under cover in autumn and winter. Midsummer sowings can also work. Avoid spring sowings outdoors; if you do sow in spring, use bolt-resistant varieties and sow direct rather than transplanting.

How do I cook pak choi?

Pak choi is best cooked briefly to preserve its crisp texture and mild, sweet flavour. The most common methods are: stir-frying (halve small heads or separate leaves for larger ones, stir-fry in a hot wok with garlic, ginger, and soy sauce for 2 to 3 minutes); steaming (halved heads steamed for 3 to 4 minutes); and wilting in a pan with a little water or stock. The white leaf stalks take slightly longer to cook than the green leaf blade, so add the stalks to the pan first and the leaves last. Baby pak choi can be halved and roasted or used raw in salads. Pak choi is also delicious added to soups, noodle broths, and curries in the final minutes of cooking.

When should I sow pak choi in the UK?

The best time to sow pak choi in the UK is late July to mid-August for autumn harvest: plants sown in this window develop in the shortening, cooler days of August and September, which are far less likely to trigger bolting than spring conditions. Sow directly into prepared ground or into modules and transplant quickly to minimise root disturbance. The second-best sowing window is under glass or fleece in September for harvest in October and November, or in an unheated greenhouse over winter. Spring sowings (March to May) are possible but risky and require bolt-resistant varieties: choose 'Joi Choi', 'Canton White', or similar spring-sowing varieties.