When to sow pak choi

Pak choi is a crop for the second half of the year. In Germany, Austria and Switzerland, sow it outdoors from early July to mid-August, or raise plants in modules from late June and plant them out by mid-August. In the UK the same window works well, and you can keep sowing into late summer under cover for autumn leaves.

The reason is bolting. Pak choi flowers readily when days are long, and a spell of cold, roughly below 50–54°F, while the plants are young pushes them the same way. A spring sowing gets both: chilly nights early on, then the longest days of the year. Plants sown after midsummer grow into warm weather and shortening days, and make leaves and stalks instead of flowers.

You can still sow in April or May if you want to try. Pick a bolt-resistant variety, keep the soil moist, and harvest early as baby leaves or small heads rather than waiting for full size.

Pak choi likes fertile, moisture-holding soil and copes with most ground where cabbages grow. It is usually sown as a follow-on crop after early peas, lettuce or new potatoes, so the bed rarely needs much preparation. Just loosen it and rake it level.

Sow thinly, 0.4–0.8 in deep, in rows 12–16 in apart. The seeds germinate within about a week in summer warmth. Two to three weeks after sowing, thin the seedlings to 10–12 in for full heads, or to about 8 in for smaller, semi-mature ones. For baby leaves, 3–4 in is plenty.

To raise plants first, sow two or three seeds per small pot or module cell and keep them warm, ideally around 68°F. After about three weeks they are ready to plant out. Plant them while they are still small: large, pot-bound seedlings settle in badly and are more likely to bolt.

A 120 × 80 cm raised bed takes three rows of four at full spacing, 12 heads. Grown to semi-mature size at 8 in, you can fit 24.

Water is the thing that matters most. Pak choi is shallow-rooted and needs a lot of it, and a dry spell is one of the quickest ways to make it bolt. Keep the soil evenly moist and water in dry weather, but don't let the bed become waterlogged. A mulch helps hold moisture in summer.

After a well-fed early crop there is usually enough nutrient left in the soil. Two to three weeks after the seedlings come up, a light top-dressing is enough, for example about 50 g of horn meal per square metre.

Full sun suits sowings made in cooler weather. In a hot spell, light shade or a cover of fine mesh keeps plants cooler and less likely to bolt, and the mesh keeps pests off too.

Full heads are ready about seven to ten weeks after sowing, or five to seven weeks after planting out, so a July sowing gives you pak choi from late August into October. For baby leaves, start picking about four weeks after sowing.

Cut the whole head just above the soil, or pick the outer leaves of young plants as you need them. Don't wait too long: once you see a flower stalk rising from the centre, harvest straight away before the stalks turn tough.

Handle it gently, because the fleshy stalks bruise and snap easily. Pak choi doesn't keep long once cut, so harvest what you'll use within a few days. In the bed it holds well until the first proper frost; a fleece cover buys you extra weeks in autumn.

Look for the words "bolt-resistant" or "slow to bolt" on the packet, especially if you want to sow before July. The Bavarian garden academy names 'Joi Choi' F1 as a suitable bolt-resistant type, and the RHS lists 'Glacier', 'Summer Breeze' and the purple-leaved 'Red Choi' among varieties with its Award of Garden Merit.

If you save seed or prefer organic, open-pollinated varieties, 'Yorokobi' from Bingenheimer is a compact type bred for autumn growing. Compact varieties also make better use of a small raised bed.

Flea beetles are the classic pak choi problem: tiny round holes pitted into the leaves, worst on seedlings. The only reliable protection is fleece or fine insect mesh laid over the row on the day you sow, with the edges weighed down. Keeping the soil evenly moist also helps.

The same mesh keeps out cabbage white butterflies, whose caterpillars eat the leaves, and cabbage root fly, whose maggots tunnel into the roots and stalk bases so that young plants wilt and collapse. Slugs and snails like the tender leaves as well, especially in a damp autumn.

Clubroot is the serious one. Pak choi is very susceptible: plants stay stunted and wilt in warm weather, and the roots swell into thick, distorted clubs. Its spores can survive in soil for up to 20 years. Liming acid soil reduces the damage, and raising plants in pots gives them a head start on infected ground, but the real answer is to keep it out of your beds.

Pak choi belongs to the cabbage family, with cabbages, kale, kohlrabi, Chinese cabbage, radishes, turnips and rocket. Leave at least three to four years before any of them grows in the same bed again, and longer if clubroot has ever appeared.

Companion planting charts pair pak choi with lettuce, spinach, onions or herbs. We found no solid evidence for any of these pairings; they are tradition. What does make sense is timing: pak choi fits neatly into a bed after an early crop such as peas, lettuce or new potatoes, as long as that crop wasn't a brassica.

The one rule with a real reason: don't grow pak choi next to or straight after other brassicas. They share flea beetles, cabbage root fly and, above all, clubroot.