Starting bok choy indoors under lights gives you a strong, early start for both spring and fall crops. After more than 30 years of seed-starting in raised-bed, year-round gardens, I’ve found that bok choy is one of the easiest greens to grow indoors—as long as it gets bright, consistent light and cool temperatures. Proper indoor growing conditions prevent legginess, help seedlings establish thick stems, and prepare them for transplanting without stress.

This guide shares the exact steps, timing, and techniques I use to reliably grow sturdy, healthy bok choy seedlings.

Table of Contents

Why Start Bok Choy Indoors?

Starting indoors allows you to:

Get a jump on cool-season planting
Protect young plants from flea beetles
Control light and temperature
Produce stocky, stress-free seedlings that resist bolting later

Indoors is especially useful for spring crops that must mature before warm weather arrives.

Best Time to Start Bok Choy Indoors

Spring Crop

Start seeds 4–6 weeks before your last expected frost
Transplant outdoors 2–3 weeks before last frost under row cover

Fall Crop

Start seeds 8–10 weeks before your first expected fall frost
Transplant outdoors when nighttime temperatures begin cooling

Over decades of growing bok choy, I’ve found that fall indoor starts often produce the best-quality heads.

Supplies You’ll Need

Seed-starting trays or small cell packs
Quality seed-starting mix
Full-spectrum LED or fluorescent grow light
Heat mat (optional but helpful for very cool rooms)
Light row cover (for hardening off later)

Step-by-Step: How to Start Bok Choy Indoors Under Lights

1. Fill Trays With a Fine Seed-Starting Mix

Use a sterile mix designed for seedlings. Bok choy’s tiny seeds germinate best in a loose, airy medium.

I avoid garden soil or heavy mixes—they slow germination and increase damping-off risk.

2. Sow Seeds Shallowly

Sow 2–3 seeds per cell
Cover with ⅛ inch of fine soil
Mist gently with water

Bok choy seeds sprout quickly, usually within 3–5 days.

3. Use Bottom Heat Only if Room Is Below 65°F

Bok choy germinates best at 65–75°F.

A heat mat is helpful in cold rooms but not essential. Too much heat can encourage legginess later.

4. Place Seedlings Under Bright Lights Immediately

This is the most important step.

Keep lights 2–3 inches above the seedlings
Provide 14–16 hours of light per day
Raise lights as seedlings grow

From long experience starting thousands of seedlings, I’ve found that close, bright light is the only reliable way to prevent tall, thin, weak stems.

5. Thin Seedlings Early

When seedlings reach 1 inch tall:

Snip to one seedling per cell
Choose the stockiest, strongest one

Thinning reduces competition and prevents stretching.

6. Keep the Soil Evenly Moist

Bok choy prefers steady moisture, not soggy soil.

Water from below when possible
Allow the top surface to slightly dry
Avoid water on leaves to prevent damping-off

A small fan on low improves airflow and strengthens stems.

7. Fertilize Lightly After True Leaves Develop

After 10–14 days:

Feed with a half-strength organic liquid fertilizer
Repeat every 10 days

Overfeeding can cause floppy seedlings, so go light.

8. Harden Off Before Transplanting

About 7–10 days before planting outdoors:

Move trays outside for a few hours a day
Gradually increase sun and wind exposure
Keep out of direct hot sun at first

My experience shows that well-hardened bok choy transplants grow faster and resist bolting better.

When Seedlings Are Ready to Transplant

Transplant when seedlings are:

3–4 weeks old
3–4 inches tall
Have 2–3 sets of true leaves

Plant outdoors during cool weather—heat-stressed transplants bolt early.

Conclusion

Starting bok choy indoors under lights is one of the simplest ways to ensure strong, healthy plants that resist bolting and mature quickly in spring or fall. With bright light, cool temperatures, and steady moisture, your seedlings will be stocky, vigorous, and ready to thrive in the garden. These steps come from decades of hands-on experience and will help you master bok choy from seed to harvest.