Bok Choy

Bok choy (Brassica rapa subsp. chinensis) is one of the fastest vegetables you can grow to a usable size. Baby bok choy - harvested at 4-6 inches tall - is ready in 30-35 days from transplant, which means a spring planting can give you a full harvest before the summer heat arrives. Full-size heads take 45-60 days. If your goal is maximum pound-per-square-foot per season, bok choy belongs in your cool-season rotation.

What you’re actually growing

Brassica rapa subsp. chinensis is a member of the rapa group - the same species as turnip (B. rapa subsp. rapa) and napa cabbage (B. rapa subsp. pekinensis). It forms a loose rosette of thick, white or green petioles and broad green leaves. Unlike most heading brassicas, it doesn’t form a tight head - the loosely packed cluster is harvested whole or leaf by leaf.

The distinction between baby and full-size bok choy is mostly harvest timing, not a different cultivar type. Baby bok choy is simply full-size bok choy harvested 2-3 weeks early. However, some varieties are bred specifically for small-head production: ‘Toy Choy’, ‘Joi Choi’, and ‘Dwarf Bok Choy’ reach 6-8 inches at maturity and are consistently tender. Standard full-size varieties like ‘White Stem’ and ‘Pak Choi Joi’ can reach 12-18 inches.

Shanghai bok choy (B. rapa subsp. chinensis var. communis) has green petioles rather than white - often sold as “Shanghai pak choi” or “green stem bok choy.” It has a slightly more delicate texture than white-stem types and is popular at specialty and Asian markets.

The ROI case

Bok choy at retail runs $2.00-$4.00/lb for full-size heads and $4.00-$6.00/lb for baby bok choy at specialty and farmers market pricing, based on USDA AMS terminal market vegetable price data. Your 1.0 lb average yield per plant at $2.50/lb returns $2.50 per full-size plant. Baby bok choy at premium prices returns proportionally more per pound on a smaller harvest.

The real advantage is speed and season overlap. A packet seeded in early spring can produce two succession harvests before summer heat triggers bolting - meaning you get two crops from one bed before your summer plants go in. Again in fall, the same sequence runs from late August through October or November in most zones. Four crops per year from one bed is achievable with tight succession planting.

Growing requirements

Direct sow in spring 4-6 weeks before the last frost date, or start indoors 4-5 weeks before transplanting. Bok choy bolts readily in response to long days and heat - spring timing is important. If you’re planting when days are already lengthening fast (after May 1 in most of zone 6), stick to baby-size varieties and harvest early. Fall planting (mid-August to early September in zone 6) is actually more reliable than spring in areas with unpredictable late cold snaps followed by sudden heat.

Seed germination is fast at 45-95°F - you’ll see seedlings in 4-7 days. Thin or space transplants to 6-8 inches for baby bok choy, 12 inches for full-size. Crowded plants go to seed faster than properly spaced ones.

Soil pH of 6.0-7.5. Bok choy is a moderate feeder. Compost incorporated before planting and a balanced fertilizer at transplanting is usually sufficient for the fast growth cycle. Consistent moisture is more critical than fertility: drought stress increases bitterness and accelerates bolting. Maintain 1 to 1.5 inches of water per week, evenly distributed.

What goes wrong

Bolting is the most common problem - the plant abruptly sends up a flower stalk and leaves become bitter and tough. It’s a response to cold temperatures followed by warming (vernalization), long days, or heat. The prevention is timing: plant early enough that the crop matures before days lengthen significantly, or plant in fall when day length is decreasing. Varieties marketed as “slow bolt” genuinely delay the response by a week or two.

Flea beetles (Phyllotreta spp.) chew tiny round holes in leaves and are the most common pest of bok choy and other Asian brassicas. Damage is mostly cosmetic but severe infestations can kill seedlings. Row cover from day one is the most effective prevention. Diatomaceous earth scattered around the base of plants reduces adults on the soil surface.

Cabbage aphid (Brevicoryne brassicae) colonizes dense rosettes, particularly in the inner leaves. A hard water spray directed into the center of the plant dislodges most colonies. Insecticidal soap for persistent infestations.

Clubroot (Plasmodiophora brassicae) is a soilborne protist that causes distorted, swollen roots and stunted top growth. It persists in soil for up to 20 years, survives a wide pH range, and has no effective chemical treatment once established. Rotate brassicas out of any bed where clubroot appears for at least 3-4 years, and raise soil pH to 7.0-7.2 which reduces pathogen activity (University of Wisconsin Extension, Clubroot of Crucifers, 2019).

Harvest and storage

For baby bok choy, harvest when plants reach 4-6 inches tall by cutting at the soil line with a sharp knife. For full-size bok choy, cut at the soil line when heads are compact and before any yellowing of outer leaves.

You can also harvest individual outer leaves and let the plant continue growing - this extends the harvest by 1-2 weeks on full-size plants. Stop this approach at the first sign of bolting.

Fresh bok choy keeps in the refrigerator for 3-5 days in a loosely closed plastic bag. The petioles wilt quickly at room temperature. Don’t wash before refrigerating - moisture accelerates decay. For longer storage, blanch for 2 minutes, cool in ice water, drain well, and freeze in zip bags. Frozen bok choy is only suitable for cooked applications.

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Related crops: Kale, Radish

Related reading: Spring Garden Planning - how to time cool-season crops to avoid the common spring bolt problem