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The plant you want is a flat, dense rosette, ten to sixteen inches (25 to 40 cm) across, sitting so low that you cannot see the stem at all from standing height. Every leaf overlaps the one below it in a spiral, and the colored center reads as the middle of a single circular object. It is closer to arranging a plant than to pruning one, because there is nothing to cut back and no branching to manage.
The failure mode is equally specific: a colored head on a bare stalk three to six inches (8 to 15 cm) tall, leaning under its own weight. Once that stem exists it will not shorten, and the plant will not branch to hide it. This is why training here is entirely about preventing the stem in the first place, over the eight to ten weeks between sowing and the first cold nights.
| Cause of a long stem | When it happens | How to prevent it |
|---|---|---|
| Seedling grown on too long in its cell | First three weeks | Plant out at three to four true leaves |
| Too little light | Any stage | Full sun all day. Never raise seedlings in shade |
| Sown too early | Before mid summer | Sow 10 to 12 weeks before first frost, not sooner |
| Plants too close together | Autumn | 10 to 12 inches (25 to 30 cm) apart minimum |
| Lower leaves lost to drought | Late summer | Keep the soil evenly moist while it is growing |
| Autumn feeding | Autumn | Stop feeding six weeks before frost |
Plant deep, and plant deep again
The one real correction available to you is burying the stem. Ornamental kale roots freely from any part of the stem in contact with damp soil, so a seedling can be set into its final position with the soil brought right up under the lowest ring of leaves, several inches deeper than it grew in the cell. This does two jobs at once: it hides the stem you already have, and the new roots that form along the buried section anchor the plant against winter wind.
You can repeat this once during the growing weeks. If a plant in the ground has visibly lengthened by early autumn, draw soil or compost up around the stem the way you would earth up a potato, up to the lowest healthy leaves. In a container, top up with fresh compost to the same level. Do not bury living leaves, and stop doing this once the cold arrives, since soil piled against the stem in freezing wet conditions invites rot.
- Judge the stem before you plant Hold the seedling and look at the gap between the soil surface and the lowest leaf. Anything over half an inch (1 cm) is stem you should bury when you plant.
- Set the plant so the lowest leaves rest on the soil Dig the hole deeper than the root ball needs and lower the plant until the leaves are just clear of the surface. Firm the soil around the buried stem.
- Water in once, thoroughly A single deep watering settles soil into contact with the buried stem, which is what triggers the new roots. Do not water again until the surface dries.
- Earth up once in early autumn if needed Draw soil up to the lowest leaves. Stop once nights are consistently cold, and never pile soil into the center of the rosette.
- Remove failing lower leaves cleanly Twist off yellowing outer leaves downward at the stem. A clean break leaves no stub to rot against the stem through the winter.
Growing one deliberately on a tall stem
The bare stem is a fault when it happens by accident and an effect when you do it on purpose. A plant grown on in a generous pot from an earlier sowing, with every lower leaf stripped off as it matures, ends the season as a colored head on a clean upright stalk a foot (30 cm) or more tall. Used singly in a pot or repeated down a row, it looks entirely intentional, which the accidental version never does.
It needs commitment from the start. Sow four to six weeks earlier than usual, pot on rather than planting out small, strip the lower leaves progressively so the stem is bare and even rather than ragged, and stake the plant early, before it needs it. The stem is not strong enough to hold a wet, frosted head against winter wind, and a cane pushed in later will go straight through the root ball. Tie loosely just under the head with soft material.
If you try this, record the sowing date, the pot size and the finished stem height. The margin between an elegant standard and a plant that snaps in the first gale is narrow, and it depends far more on your own wind exposure than on any general rule.
Wind, weight and staking in the ground
A well grown low rosette needs no support at all. Its own width and the buried stem take care of it, and it will sit through gales and snow unmoved. Snow on top of the rosette is not a problem and often protects the color; brush off only what has frozen into a heavy crust.
Plants that have lengthened despite everything will lean, and the lean gets worse once the head is wet and frozen. Push a short cane in on the windward side, close to the stem but angled away from the root ball, and tie once just below the leaves. Straightening a leaning plant by pulling it upright tears roots, so instead lift it, replant it deeper, and firm it in. Autumn is late for that but ornamental kale transplants far better than most plants and will usually re-root within a fortnight if the ground is not yet frozen.