Bok choy grows fast — 45–60 days — and it bolts the moment it feels heat or stress, which is why indoor starting earns its keep: you control the early weeks, keep the seedlings cool and steady, and plant them out into cool spring soil.
Bok Choy belong to the Brassicaceae family, need part shade, and take 45–60 days to mature, with seed germinating in 7–10 days. That combination — a moderate season and fairly quick germination — shapes every decision in this guide, from when you sow to whether indoor starting is even worth it. Bok choy is one of the few brassicas where indoor starting is genuinely useful for a spring crop: the seed germinates in 7–10 days, the seedlings grow fast, and a transplant that goes out into cool soil with steady water is far less likely to bolt than a direct-sown plant caught by a hot spell. It also tolerates part shade, which helps in warm zones. The key is to keep seedlings cool and never let them dry out or get root-bound.
Bok Choy at a glance
| Growing factor | What bok choy need |
|---|---|
| Days to germination | 7–10 |
| Sowing method | both |
| Days to maturity | 45–60 |
| Soil pH | 6.0–7.5 |
| Spacing | 8–12 inches |
| Sun | part shade |
| Cold tolerance | hardy |
| Water needs | moderate |
| Family | Brassicaceae |
When to start bok choy seeds indoors
In Zones 3–6, start bok choy indoors 4–6 weeks before your last frost, or direct-sow 2–3 weeks before. In Zones 7–9, grow bok choy as a fall and winter crop — start indoors in late summer. In Zones 10–13, sow through the cool season. Bok choy bolts in heat, so cool-season timing matters more than anything.
Timing in brief: start indoors 4–6 weeks before your last frost, or direct-sow 2–3 weeks before. Work backwards from your last frost date using our seed-starting calculator and the frost-date calculator, and confirm the timing with your local extension service. Zones 11–13 are frost-free, so never plan around a frost date there — the calendar in those zones is about heat and rain instead. If you are unsure of your zone, the hardiness-zone finder will confirm it.
What you need
- Fresh bok choy seed — check the packet date, and test old seed before you rely on it
- Seed trays or cells, plus peat pots or soil blocks if you are starting a crop that dislikes root disturbance
- Fine, sterile seed-starting mix — not garden soil, which is too heavy and carries disease
- A spray bottle or a tray for bottom watering
- Labels and a marker — bok choy seedlings all look alike at first
- A grow light, or the brightest windowsill you have
- A heat mat, if you are starting a warmth-loving crop or your room runs cool
- Clean water, and a small fan for air circulation once seedlings emerge
Keep the seed packet as your reference for variety, sowing depth, and days to maturity. Wash reused trays in hot soapy water first — old compost is where damping-off fungi live.
Step by step: starting bok choy seeds indoors
Sow bok choy seed 1/4 inch deep in cells — one or two seeds per cell. Germination takes 7–10 days. Thin to the strongest seedling and grow on cool and bright until plants have three or four true leaves.
- Fill your containers. Fill trays, cells, or peat pots with moist seed-starting mix, damp like a wrung-out sponge. Water dry mix before you sow, not after.
- Sow at the right depth. Sow at the depth on the packet and no deeper — seed sown too deep runs out of energy before it reaches the surface.
- Label everything. Write the variety and sowing date on every tray.
- Water gently. Mist the surface or water from below so seed is not washed away. Cover the tray to hold moisture in, and remove the cover the moment seedlings appear.
- Keep it warm and bright. Seed germinates in 7–10 days in suitable conditions — check daily, and move the tray into light the moment green appears.
- Thin to the strongest. If two seedlings share a cell, snip the weaker one at soil level — pulling disturbs the roots of the one you keep.
- Pot on when ready. Move seedlings into individual pots once they have two or three true leaves, handling them by a leaf, never the stem.
- Feed lightly. Seed mix has almost no nutrients, so once seedlings have true leaves, feed at half strength with a balanced liquid feed every week or so.
For direct-sown crops, the outdoor version is simpler: sow where the plant will grow, keep the bed moist until germination, and thin to 8–12 inches apart. The soil pH for bok choy should be 6.0–7.5.
Light for seedlings
Bok choy seedlings need strong light to stay stocky. A grow light a few inches above the leaves for 14–16 hours a day is ideal; a dim windowsill gives you leggy plants that bolt early.
Give seedlings 14–16 hours of light a day. A south-facing windowsill can work in spring, but most seedlings do better under a grow light hung a few inches above the leaves and raised as they grow — if the light is too far away, seedlings stretch and go leggy, and leggy seedlings rarely recover. Our grow-light calculator can help with hanging height and hours. Give them a dark night too; do not leave lights on around the clock.
Watering seedlings
Keep compost evenly moist during the 7–10 day germination window. Bok choy needs moderate, steady water — a dry spell or a check in growth is often what triggers bolting.
Water seedlings from below whenever you can: stand the tray in a shallow dish for ten minutes, let the mix soak it up, then drain it away. Top watering washes seed around and keeps the surface wet, which invites damping off. Keep the mix evenly moist — never soggy, never dry — and check daily, because a small cell dries fast under lights and a dry spell during the 7–10-day germination window can stall the seed. Once seedlings have true leaves, let the surface dry slightly between waterings. Our watering calculator gives a starting point. Use room-temperature water — cold water shocks young roots.
Hardening off
Harden bok choy off over 7–10 days. It is hardy and tolerates cool nights, but harden gradually — a stressed transplant bolts.
Hardening off means getting indoor seedlings used to the outdoors gradually, over 7–10 days. Start with a few hours in a sheltered, shady spot, then lengthen the time outside each day and introduce more sun and wind. Bring trays in at night for the first few days, especially if frost threatens. Seedlings put straight outside without hardening off wilt, scorch, or stop growing for weeks — the shock undoes all the careful indoor work.
Transplanting outdoors
Set bok choy 8–12 inches apart in fertile, moisture-retentive soil in full sun or part shade. Plant at the same depth as in the pot, water in thoroughly, and mulch to hold moisture. Harvest whole heads when they feel firm.
Bok Choy grow best in part shade and a soil pH of 6.0–7.5, so choose the sunniest suitable spot and test the soil before you plant. Good companions nearby include marigolds, basil, onions. Space plants 8–12 inches apart — crowding is one of the commonest causes of small harvests. Our plant-spacing calculator works out how many plants fit your bed. Plant on a cloudy day or in the evening, water in thoroughly, and mulch to hold moisture.
Common problems and fixes
| Problem | Fix |
|---|---|
| Cabbage Worms | Check plants regularly, remove by hand, and cover young plants with insect mesh. |
| Aphids | Spray off with water and encourage beneficial insects. |
| Damping off | Use fresh sterile seed mix, water from below, and give seedlings good air circulation. |
| Leggy seedlings | Move grow lights closer — a few inches above the leaves — and give 14–16 hours of light a day. |
| Seed not germinating | Check the seed is fresh and the compost is moist; bok choy seed takes 7–10 days to germinate. |
Bolting before heads form
Heat, drought, or transplant stress. Keep seedlings cool, water steadily, and transplant young.
Flea beetles
Tiny beetles make shot-holes in leaves. Cover young plants with insect mesh.
Leggy seedlings
Too warm and too dark. Grow seedlings on cool and bright.
Frequently asked questions
Is bok choy better started indoors or direct-sown?
Both work, but indoor starting gives you more control over the cool, steady early growth that prevents bolting. Direct sowing is fine in cool weather with steady water.
Why did my bok choy bolt?
Usually heat, drought, or a check in growth. Sow in cool seasons, keep water steady, and transplant young without disturbing roots.
Can bok choy grow in shade?
Yes — bok choy tolerates part shade, which is an advantage in warm zones where full sun brings heat and bolting.
How long do bok choy seeds take to germinate?
Bok Choy seed takes 7–10 days to germinate in suitable conditions. Keep the compost moist and at room temperature, and use fresh seed — old seed germinates slowly or not at all. Our germination-time calculator can help you work out the timing for your sowing.
Can I use old bok choy seed?
Check it first. Seed viability falls with age and poor storage, so test a few seeds on damp kitchen paper before sowing a whole tray. Our seed-viability checker walks you through the test.