Gadenin日本語Get the appSow into soil that is already warm
Bok choy germinates fast. In soil at 68 to 77F (20 to 25C) it is up in three to five days, and at 59F (15C) it takes a week or more and comes up unevenly. Below 50F (10C) germination is slow enough that slugs and damping off take most of the seed before it ever emerges.
The reason to care about soil temperature is not only germination speed. Bok choy is one of the brassicas that reads cold as a signal to flower. A seedling that spends a week or two below about 50F (10C) once it has a few true leaves will run to seed weeks later, when the weather has turned mild and everything looks fine. The bolt you see in late spring was decided by the cold snap you sowed into.
Push a soil thermometer four inches (10 cm) down and read it in the morning, not the afternoon. Morning is the low point of the day, and it is the low point that triggers the response.
| Soil temperature | Days to emerge | What to expect |
|---|---|---|
| Below 50F (10C) | Ten days or more | Patchy stand, and a real bolting risk later |
| 54 to 59F (12 to 15C) | Six to eight days | Usable, but keep row cover over the bed at night |
| 64 to 77F (18 to 25C) | Three to five days | Even stand. This is the target range |
| Above 86F (30C) | Four to six days, thin | Germination drops off and seedlings stretch |
Depth, spacing and how many seeds per station
Sow half an inch (1 cm) deep. Deeper than that and the fast shallow emergence you want turns into a slow weak one. Firm the soil over the seed with the back of a rake so it sits in contact with moist soil rather than in an air pocket.
Spacing is where you decide what you are growing. Bok choy at four inches (10 cm) makes the small tender heads sold as baby pak choi, and the same seed at ten inches (25 cm) makes a full head with a thick white rib. It is one plant at two spacings, not two crops, so you can sow the whole bed alike and take some early as baby heads to open the spacing for the rest.
| What you want | Row spacing | Plant spacing | Weeks to cut |
|---|---|---|---|
| Baby heads | 8 in (20 cm) | 4 in (10 cm) | Three to four |
| Mid size | 10 in (25 cm) | 6 in (15 cm) | Five to six |
| Full heads | 12 in (30 cm) | 10 in (25 cm) | Seven to nine |
| Cut and come again leaf | 6 in (15 cm) | 2 in (5 cm) | Three |
Sow three or four seeds per station rather than a continuous line. The seed is cheap and germination is high, so station sowing gives you a choice of seedling at each spot and much less thinning waste.
Thin in stages, and eat the thinnings
Thinning is not optional here. Crowded bok choy stretches, the ribs stay thin, and the damp still air inside a thick stand is what turns flea beetle and slug damage into rot. Thin three times rather than once, and take the pressure off gradually.
- At the seed leaves As soon as the round seed leaves have opened, take each station down to two or three seedlings. Pull the ones with bent or discolored stems first; they do not catch up.
- At two true leaves Reduce to two per station, keeping the plant with the shortest distance between the seed leaves and the soil. A stretched seedling stays weak for the rest of its life.
- At four true leaves Go to one plant per station at your final spacing. The thinnings at this stage are a salad, which is the point where thinning stops feeling like waste.
- Firm the survivor back in Pulling neighbors loosens the plant you keep. Press the soil back around it with your thumbs and water it in, or it will sulk and wilt for two days.
Modules and transplanting
Bok choy transplants well as long as it is young. Sow two seeds per cell in a module tray, thin to one, and plant out at three to four true leaves, about three weeks from sowing. Past that the root circles the cell and the plant checks badly when it goes out, which is another way to trigger bolting.
Water the tray an hour before you lift, plant at the same depth the seedling was growing, and firm it in. Do not bury the growing point in the middle of the rosette. If soil gets down into the crown the plant rots from the center outwards.
Put the mesh over the bed the same day you sow or plant, not the week after. Flea beetle finds bok choy seedlings within a day or two of emergence, and a covered bed is far easier than a rescue.
What to write down at sowing
Bok choy runs its whole life in six to nine weeks, so the record of one sowing is still useful for the next one in the same season. Write down the sowing date, the morning soil temperature at four inches (10 cm), the date of emergence, and the spacing you used.
Then add one line at the end of the crop: whether it bolted, and how many nights it saw below 50F (10C) in between. Two seasons of that and you will know the earliest date your own garden can take a spring sowing, which is a number no seed packet can tell you.