Why are my cabbages not hearting up?

The order matters and it explains everything. A cabbage spends most of its life making large spreading outer leaves, and only then starts folding new leaves inwards into a dense heart. Anything that interrupts the first phase costs you the second, and by the time you notice the open rosette in autumn the decisive weeks are behind you.

Step by step

1. Give them the full spacing.Summer cabbage around 35–45cm apart, larger winter and savoy types 45–60cm. Crowded plants shade each other, never build a frame, and stand open all season. This is the commonest cause.
2. Plant firmly — really firmly.Brassicas want a solid root anchorage. Heel the soil in hard around the stem with your boot, then tug a leaf: the leaf should tear before the plant moves. A rocking plant repeatedly breaks its fine roots and stalls.
3. Keep them going through midsummer.A dry fortnight or a run out of nitrogen in July, right when the frame should be expanding, is a check the plant may never make up. Water thoroughly in dry spells and give a nitrogen-leaning feed midway through growth.
4. Sow the right type at the right time.Cabbage varieties are bred for specific seasons — spring, summer, autumn, winter and savoy — and the sowing window is narrow. A variety sown well outside it grows leaves and never hearts.
5. Draw soil up around the stems in autumn.Earthing up the stems of tall winter brassicas stabilises them against wind rock, which is the main cause of loosening after planting. Stake sprouts and tall kale on exposed sites.
6. Check for root problems if plants stay small and wilt in sun.Stunted brassicas that wilt in sunshine on damp soil should be dug up and inspected. Swollen distorted roots mean club root and the plant will never heart.
7. Net against pigeons and caterpillars.A plant that keeps losing leaf area cannot build a frame. Netting is the difference between a plant that hearts and a stripped stalk in many gardens.
8. Be patient with winter types.Winter cabbages and savoys heart up slowly and late, often not until deep autumn. A plant that looks open in September may be perfectly on schedule.

Tips

• Loose leaves from a non-hearting cabbage are perfectly good food — cook them like spring greens rather than writing the plant off.
• Brassicas prefer a firm, limed soil near neutral. On very acid ground, liming the brassica bed improves both growth and club root resistance.
• Raise plants in modules or a seedbed and transplant rather than sowing where they will grow — it gives you control over spacing and lets you plant into a bed that is still finishing another crop.
• A collar of card or membrane around the stem at planting deters cabbage root fly, which is another cause of a stunted plant that never hearts.

Common mistakes

• Planting into fluffy, freshly dug soil — Brassicas need firm ground. Loose soil lets the plant rock and its fine roots break repeatedly.
• Spacing by how small the transplants look — A cabbage transplant is a few centimetres across and the mature plant is half a metre. Space for the finished size.
• Sowing whatever cabbage seed is in the tin — Cabbage types have narrow, specific sowing windows. The wrong type for the season produces exactly this failure.

If it doesn't work

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