Bok Choy

Sow seed a quarter to a half inch deep in fertile, well-drained soil at pH 6.0 to 7.5, three seeds every 12 inches for dwarf varieties or every 18 inches for full-size heads, then thin to one plant per spot. Work compost or well-rotted manure in beforehand, and skip fresh manure. Bok choy is a fast, shallow-sown brassica that wants steady moisture and fertility to size up before heat arrives, and crowded plants stall into small, tough heads.

Start seed in 72- or 128-cell trays 2 to 4 weeks before setting out, and transplant while the roots still fill the cell loosely. Do not set out seedlings that are rootbound, wilted, or have been sitting stressed in the tray. Transplant stress and rootbound roots both read to the plant as the end of its vegetative life, and it responds by throwing a seedstalk instead of a head.

Lay a lightweight floating row cover over the bed at sowing or transplanting and seal the edges to the soil with pins or buried soil, or hoop it into a low tunnel. It must be on before the cabbage maggot flies begin flying - locally, that is about when yellow rocket blooms. The cover is a physical barrier: cabbage maggot flies cannot reach the soil to lay eggs, and flea beetles cannot reach the cotyledons. There is no rescue treatment once maggots are in the roots, so exclusion is the whole game.

Sow again in midsummer so the plants size up as days shorten and nights cool. Same depth and spacing as spring. Keep the seedbed damp; summer soil dries out fast and a checked seedling never recovers its vigor. Maturing into shortening days and cooling temperatures sidesteps the cold-then-warm swing that triggers bolting, which is why fall is the dependable bok choy season in most of the country.

Use a starter fertilizer when you transplant, then side-dress about three weeks later, watering it in so it reaches the roots. Bok choy is a medium-feeder: its nutrients can come from soil organic matter or from fertilizer. Bok choy is a succulent leafy crop with a medium nutrient demand and a 45-to-50-day run; the nitrogen has to arrive while the leaves are still expanding or you get small, fibrous stalks.

Check seedlings for tiny jumping beetles and their shotgun-hole feeding. At the cotyledon stage, treat if you find one beetle per transplant, or five beetles across ten transplants. Once plants are past 4 to 5 true leaves they tolerate far more feeding - the threshold rises to about 4 beetles per plant at 3-6 inches tall and 8 per plant above that - so established plants rarely need anything. Flea beetles overwinter as adults in debris and move in from cruciferous weeds in spring; a seedling has so little leaf area that the same feeding that a mature plant shrugs off will kill it outright.

Sample 25 plants weekly from emergence, looking for velvety green caterpillars and greenish-brown fecal pellets. On young plants, treat at about one caterpillar per five plants. Spray Bacillus thuringiensis and cover the leaf undersides and the center of the plant where they feed. Bt has to be eaten to work and only kills early-instar larvae, so it is very effective on young caterpillars and nearly useless on big ones - the timing, not the product, decides the result.

Cut the whole plant off at soil level once it carries 10 to 15 leaves - roughly 40 to 50 days from seeding. Dwarf types are ready around 6 inches, full-size around 12. You can also pick individual outer leaves as you need them and leave the plant standing. Held past maturity the plant turns bitter and then bolts, and a bolting plant pours its sugars into the seedstalk rather than the stems you are growing it for.