If your red cabbages are producing lots of leaves but no firm heart, the most likely causes are old seed, too much nitrogen, or growing them in the wrong season.

Start by checking the seed packet date, as cabbage seed is usually viable for up to four years. If the seed is old, germination and plant performance can both suffer.

Another factor is soil nutrition. Too much nitrogen fertiliser encourages soft, leafy growth, which can stop cabbages from forming a dense heart. If plants are growing plenty of leaves but not heading up, this is often part of the problem.

It may also help to change your timing. Red cabbages are often easier to grow over the cooler months rather than as a summer crop.

For better results, try this:

• Plant in late March to early April
• Choose a sunny site
• Prepare the soil well with Garden Time™ Compost before planting
• Avoid overdoing high-nitrogen fertilisers

By planting in autumn, young cabbage plants can establish a strong root system before winter. In cooler conditions, they are more likely to develop a dense heart and should be ready to harvest in late winter.

You could also try planting seedlings from your local garden centre instead of sowing from seed, as there are usually good red cabbage varieties available and they give you a head start.