Gadenin日本語Get the appSow in mid to late summer, not in autumn
This is the single decision that settles how good the plant looks in winter. Ornamental kale needs roughly ten to twelve weeks of growing before the cold arrives, because it has to build a wide rosette of leaves first and only then color it. Sowing has to happen in the hottest part of the year, eight to ten weeks before your first frost date, which always feels wrong at the time. Every week you delay past that point comes off the finished width of the plant, and a narrow plant colors just as well but reads as a small tuft rather than a rosette.
Sown too early is a real fault too, though a less common one. A plant sown in early summer runs on for months in warm weather, stacks up leaf after leaf on a lengthening stem, and arrives at the cold season tall and gappy with an obvious bare stalk under the head. Aim for a plant that is around six to eight inches (15 to 20 cm) across and still tight when the nights start dropping into the forties Fahrenheit (single figures Celsius).
| Weeks before first frost | Stage the plant should be at | What you do |
|---|---|---|
| 10 to 12 | Seed in cells | Sow. Germinate somewhere shaded and cool |
| 8 to 9 | Three to four true leaves | Plant out into the final bed or pot |
| 4 to 6 | Rosette 6 to 8 inches (15 to 20 cm) across | Stop feeding. Leave it alone |
| 0 to 2 | Full width, still green | Wait. Color follows the cold, not the calendar |
Germinating in summer heat
The seed itself germinates fast, in three to five days at 68F (20C), and will come up over a range from about 45F to 80F (7C to 27C). Above 80F (27C) germination gets erratic and the seedlings that do emerge stretch badly in the first three days, which is the beginning of the long bare stem you are trying to avoid. Since you are sowing in the hottest weeks of the year, the whole job is about keeping the seed cooler than the air around it.
Sow into cells or small pots rather than the open ground. Stand them in bright shade, not full sun, and water enough to keep the surface dark and damp twice a day. The moment the first seed leaves show, move the tray into full light. Seedlings held in shade for even two extra days after emergence stretch, and once a seedling has stretched there is no fixing it.
- Fill 2 inch (5 cm) cells and firm lightly Use a free draining seed-starting mix. Cells this size hold enough moisture through a hot afternoon but are small enough that you are forced to plant out on time.
- Sow two seeds per cell, quarter inch (5 mm) deep The seed is small and cannot push through more than that. Cover with sieved compost and firm with a fingertip so there is no air gap under the seed.
- Keep in bright shade until emergence Three to five days. Water twice a day in hot weather. A sheet of shade cloth or a north facing bench is enough.
- Move into full sun the day they emerge Full light from day one keeps the stem short. Pinch out the weaker of the two seedlings at the first true leaf rather than pulling it, so you do not disturb the one you keep.
- Plant out at three to four true leaves That is roughly three weeks from sowing. Do not let it go longer. A plant that fills its cell and starts circling has already begun to build the bare stem.
Why small transplants beat big ones
The strongest instinct with ornamental kale is to grow the seedling on in the pot until it looks like something worth planting. It is the wrong instinct, and it costs you the plant's shape. A rosette plant lays down its leaves in a spiral on a short stem, and the stem lengthens whenever the plant is under any check, is short of light, or is simply kept growing too long before it settles into its final position. A pot bound seedling suffers all three at once.
The visible result appears in winter, when the colored head sits several inches up on a thin, leafless stalk and the whole thing leans. In the ground it can be partly hidden by planting deep, but in a container it is exposed. Planting out at three to four true leaves, when the seedling still looks too small to bother with, is what gives you a low, wide rosette sitting almost on the soil.
Write down the sowing date and your first frost date in the same place. Nearly every complaint about ornamental kale, whether it is a leggy stem or a plant that never got wide, traces back to the gap between those two numbers. One season's record turns the timing from guesswork into a fixed rule for your garden.
Spacing and where the seedlings go
Set plants ten to twelve inches (25 to 30 cm) apart if you want each rosette to be seen as a separate object, which is how they look best in a bed edge or a row along a path. At that spacing the leaves of neighboring plants just touch by midwinter. Closer than eight inches (20 cm) they shade each other's lower leaves, those leaves yellow and drop, and you get the bare stem again from a different cause.
In containers, one plant to a six to eight inch (15 to 20 cm) pot, or three in a twelve inch (30 cm) bowl set in a triangle. Plant deeper than the seedling sat in its cell, right up to the lowest leaves. Ornamental kale roots readily from the buried stem, which both anchors it against winter wind and shortens the visible stalk from the start.