Gadenin日本語Get the appThe shape of the season
The crop divides cleanly into three phases. First, roughly three weeks from sowing to a transplant with three or four true leaves. Second, four to six weeks of frame building, when the plant grows a wide rosette of large outer leaves in still-warm conditions. Third, three to four weeks of head filling, once nights fall toward 50F to 60F (10C to 15C) and the inner leaves close over.
There is almost no slack anywhere in that sequence. Every week lost to a check, a dry spell or a pest attack comes off the end, and the end is when the head fills. That is why this crop rewards preparing the bed in advance and having mesh and hoops ready before the seed goes in, rather than reacting as things come up.
| Stage | Timing | Main jobs | Decision point |
|---|---|---|---|
| Bed preparation | Two to three weeks before sowing | Compost dug in, pH checked and corrected, hoops and mesh ready | If pH is below 5.8, this bed will give tip burn. Lime now or use another bed |
| Sowing | Late summer, counting back from first frost plus two weeks | Sow half an inch (10 mm) deep, three seeds per station, shade the row, mesh it | Soil above 86F (30C) means shading is not optional |
| Emergence to thinning | Days 3 to 14 | Thin to one per station at the second true leaf, keep the surface damp | Stretched seedlings mean too little light. Fix now or accept small heads |
| Planting out (cell-raised only) | Days 18 to 22 | Plant at 14 to 16 inches (35 to 40 cm), water in, re-close the mesh | Roots circling the cell means plant today, even if the bed is not perfect |
| Frame building | Weeks 3 to 8 | Nitrogen feed at weeks 3 and 5, deep watering twice weekly, pest checks | Pale leaves at week 4 mean feed now, not later |
| Cupping | Around weeks 7 to 9 | Stop nitrogen, pull mulch back from stems, strip flat lower leaves | If the center is still open and flat well past this point, no head is coming |
| Head filling | Three to four weeks after cupping | Even deep watering, slug patrols after dark, squeeze test every few days | Uneven watering here is what causes tip burn inside the head |
| Harvest | 55 to 85 days from sowing | Cut in the morning, keep wrapper leaves, store cold and dry | Hard freeze forecast means cut everything, ready or not |
The three decisions that actually matter
Most of the schedule is routine, but three moments carry nearly all the outcome. Getting these right is worth more than perfect attention to everything else, and each of them has a narrow window where the right action is obvious and after which it is too late to do anything useful.
They are the sowing date, the moment the mesh goes on, and the point at which you stop feeding nitrogen. None of them can be corrected afterwards, which is exactly why they matter more than the daily jobs that surround them.
- Fix the sowing date first Take your average first frost, subtract the days to maturity for your seed, then subtract another two weeks. Sow in that week. Everything else in the season is downstream of this one decision.
- Mesh on the day you sow Not the day you see holes. Late-summer flea beetle and cabbage moth pressure is at its annual peak exactly when your seedlings are at their most vulnerable.
- Stop nitrogen at cupping The moment the youngest leaves stand up and curve inward, feeding stops. Nitrogen after this point gives soft inner leaves, a loose head and soft rot in wet weather.
- Change nothing about the water From cupping to harvest, keep the water deep and regular. Swings between dry and soaked during filling are the direct cause of tip burn on the inner leaves.
A second sowing, and succession
If the season is long enough where you garden, a second sowing 10 to 14 days after the first spreads the harvest and insures against a bad fortnight of weather. Do not push it further than two sowings in autumn, because the third will run into cold weather with too small a frame and give you nothing but loose rosettes.
Where winters are mild, an alternative is a late sowing grown deliberately for loose leaves rather than heads, cut young over several weeks. Treat that as a different crop with different expectations, and sow it at closer spacing, around 8 inches (20 cm), since no head has to fill.
Two sowings of the same type ten days apart tell you more about your local timing than two different types sown on the same day. Keep the variable to one thing per season and the notes stay readable.
Clearing the bed
Once the heads are cut, take the roots and the outer leaves off the bed rather than digging them in. Brassica debris carries aphid colonies, caterpillar pupae and, where it is present, clubroot, and turning it into the soil holds all of that in place for the next crop. Compost it well away in a hot heap or dispose of it.
Then mark the bed in your rotation notes as having grown brassicas this season, and keep the family off that ground for three or four years. Napa cabbage shares its soil-borne problems with cabbage, radish, turnip, mustard and rocket, so the rotation only works if you count all of them together.
What to record through the season
Keep a short entry at each of the eight stages in the table rather than trying to write everything at the end. The dates that matter most are: sowing, emergence, planting out, the day cupping began, and the day of harvest. Add the weather during the frame-building weeks and the date of the first light frost.
At the end of the season, put your harvest date against your sowing date and work out the real days to maturity you achieved. Compare it with the figure on the packet. The gap between the two is your local correction factor, and once you know it, the sowing window stops being guesswork and the loose-head years generally stop with it.