Why Are My Cabbage Leaves Loose and Not Curling In?

A cabbage with good outer leaves and a visible growing centre that begins to form layers but then stays open and floppy — the inner leaves not curling tightly inward to form a solid ball or pointed head — is producing a loose head. This is different from failing to head entirely; the plant is making an attempt but the leaves are not becoming sufficiently compact. Loose, open heads are usually usable but less dense and harder to store, and in extreme cases may be more correctly described as a large rosette than a head at all.

Excess nitrogen

Too much nitrogen applied during the heading period — particularly a heavy nitrogen feed when the plant is already forming its head — promotes continued vegetative (leaf) growth rather than the consolidation and tightening of the head. The inner leaves keep growing outward and expanding instead of folding inward. High-nitrogen feeding should be completed in the early vegetative phase; once the head is clearly forming, switch to a low-nitrogen or potassium-rich feed, or stop feeding entirely. Avoid fresh manure around cabbages at planting time — it releases nitrogen unpredictably through the summer.

Warm temperatures during hearting

As with failure to heart completely, warm temperatures during the heading phase produce loose, less compact heads. The inner leaf tissue grows rapidly in warm conditions but does not pack tightly. Cool nights (below 15°C) are particularly important for firm head formation in most cabbage types. This is one reason autumn cabbages maturing from September onward tend to produce the firmest, densest heads of the year — they form in progressively cooling conditions.

Savoy versus ball-head varieties

Savoy cabbages (crinkle-leafed types) always look more open and loose than Dutch ball-head or pointed varieties — this is their natural characteristic and not a defect. If you are comparing your savoy to a picture of a smooth ball-head variety, they will always look different. Evaluate each variety against its own type. Savoys are also the most cold-tolerant and best flavour-improved by frost among the heading cabbages.