Gadenin日本語Get the appThe right seedling has four to six true leaves
A cabbage transplant is at its best with four to six true leaves and a stem short enough that the lowest leaves almost touch the compost. That plant is about four to five weeks old from sowing and it will keep growing without a pause once you set it out. A younger plant with only two or three leaves is fragile and slugs will find it before it establishes.
The bigger risk is going the other way. A cabbage held in a small cell until it has eight or nine leaves has already run out of root room, and it never fully recovers. It heads late, the head stays small, and in warm weather it is far more likely to bolt instead. If your plants have got ahead of you, pot them up into something larger rather than leaving them in the tray.
| What you see | Stage | What to do |
|---|---|---|
| Two or three true leaves | Too young to plant out | Grow on another week or two under cover |
| Four to six true leaves, stem thick | Ready | Plant out within a few days |
| Long pale stem, leaves widely spaced | Grown in poor light | Plant deep, up to the seed leaves, and stake nothing |
| Eight or more leaves, roots circling | Held too long | Pot up now, expect a smaller head |
Sowing in cells, not straight into the bed
Cabbage germinates readily at soil temperatures between 59F and 77F (15C to 25C), usually breaking the surface in four to seven days. Sow a quarter of an inch (5 mm) deep in cells or small pots rather than direct into the bed. Raising them in cells means you control the moisture, you can keep them under insect mesh while they are tender, and you plant a healthy root system into a bed you have already prepared.
Above about 86F (30C) germination becomes unreliable and the seedlings come up thin and stretched. For a crop that will head in cool weather, sow in a shaded spot outdoors and move the tray into full light as soon as the seed leaves open. Light matters immediately: a tray left in dim conditions for even three days gives you stretched seedlings you cannot fix.
- Sow two or three seeds per cell Sow shallow, a quarter of an inch (5 mm), and cover lightly. Two or three seeds per cell insures against poor germination, and you thin later.
- Move into full light on day one The moment the seed leaves show, the tray needs the brightest position you have. Seedlings stretch within days in weak light and never thicken up again.
- Thin to one at the first true leaf When the first true leaf appears, cut the weaker seedlings off at the base with scissors. Pulling them tears the roots of the one you are keeping.
- Keep mesh over the tray Cabbage moths and flea beetles find seedlings quickly. Fine insect mesh over the tray from sowing day is far easier than treating an infestation later.
Water the tray in the morning and let the surface dry by evening. Cells that stay soaking wet overnight are how damping off starts, and a seedling that flops at the base cannot be saved.
Harden off for a week before planting out
A seedling raised under cover has soft leaves and thin cuticles. Put it straight into open ground, wind and full sun and it checks badly: the leaves scorch at the edges, growth stops for a fortnight and the head that eventually forms is a size smaller. A week of gradual exposure prevents all of that.
Start with two or three hours outdoors in a sheltered, part-shaded spot and build up to a full day and night outside by the end of the week. Ease off the watering slightly at the same time, so the plant firms up rather than staying lush. A hardened cabbage seedling has slightly bluish, stiffer leaves and a stem you can feel is woody at the base.
- Days one and two Two to three hours outdoors in shade and out of the wind, then back under cover. Do this in the morning rather than the afternoon.
- Days three to five Half a day in full sun, brought back in at night. Water only when the compost surface is dry to the touch.
- Days six and seven Leave the plants out day and night. If they look the same in the morning as they did the evening before, they are ready to plant.
What a poor root system looks like
Slide a plant out of its cell before you buy or plant it. You want white roots reaching the edge of the compost and just beginning to turn at the bottom, with the compost holding together when you lift it. That plant will push new roots into your soil within days.
Brown, soft roots mean it has been standing wet. A dense mat of roots wound round and round the outside means it has been in that cell too long, and unless you tease the bottom third apart with your fingers those roots will keep circling underground and the plant will stay stunted. Compost that falls away completely means the root system is too small to plant yet.
If you find swollen, distorted roots with knobbly galls on a plant, do not plant it and do not compost it. That is clubroot, it lives in soil for many years, and one infected transplant can contaminate a bed for a decade.
Write down the sowing date
Note the date you sowed, the date you planted out and how many leaves the plant had when it went in the ground. Cabbage varies enormously in how long it takes from transplant to a cut head, roughly 60 to 100 days depending on type and temperature, and the only reliable numbers are the ones from your own garden.
One season of records tells you whether your plants are going out too small, too large or about right, and it lets you work backwards from the weather you want at heading time to the week you should be sowing. Note the position of each plant in the bed too, because if clubroot or a soil pest shows up you will want to know exactly where it was.