Bok choy is a cool-season leafy vegetable in the cabbage family, grown for its thick white or green stalks and tender leaves. It matures quickly, often in 30–50 days, making it useful for early spring and fall harvests when most other greens are slow. Despite the label "wild mustard," this is a cultivated Brassica rapa, not the roadside weed.
It grows best in cool weather and bolts (sends up a flower stalk) when days lengthen and temperatures climb above the mid-70s°F. Sow it early in spring or in late summer for fall, keep the soil consistently moist, and harvest before heat triggers bolting. Plants tolerate light frost, which can improve flavor.
Clubroot
Swollen, distorted roots; wilting in midday heat; stunted growth and yellowing foliage. Plants recover poorly even with watering.
Remove and destroy infected plants with roots. Raise soil pH toward 7.2 with lime. Improve drainage and rotate out of brassicas for several years.
Black Rot
Yellow, V-shaped lesions spreading inward from leaf margins, with blackened veins. Severe cases cause wilting and leaf drop.
Remove and destroy infected plants. Use disease-free seed, rotate brassicas on a 3-year cycle, avoid overhead watering, and keep tools and beds clean.
Downy mildew
Yellowing on top of leaves with grey-purple fuzz underneath. Spreads rapidly in humid conditions.
Remove affected leaves. Improve air circulation. Avoid overhead watering. Copper spray as preventive.
Flea Beetle
Small round shot-holes scattered across leaves; tiny dark beetles that jump when disturbed. Heavy feeding stunts young plants.
Use floating row covers on seedlings. Remove crop debris and weeds that harbor beetles. Apply kaolin clay or spinosad if damage is severe.
Cabbage Worm
Ragged holes in leaves and green velvety caterpillars on undersides; dark green frass collects in leaf crevices and head.
Handpick caterpillars and eggs. Apply Bacillus thuringiensis (Bt) weekly during egg-laying. Use floating row cover to exclude white cabbage moths.
White Rust
White, blister-like pustules on the undersides of leaves with yellow spots on the upper surface; severe infections distort leaves and stems.
Remove and destroy infected leaves, improve air circulation, avoid overhead watering, and rotate brassicas to a new bed each year.