Why are my Brussels sprouts loose and open instead of tight?

A Brussels sprout is a tightly folded bud in a leaf axil, and it only stays tight if the plant is growing steadily and standing still. Anything that makes it grow soft — too much nitrogen, warm wet autumn weather — or that makes it move — loose planting, wind on a tall plant — produces loose, open, cabbagey buttons instead.

Step by step

1. Plant into firm, settled ground.Sprouts want soil that has not been recently dug loose. If you have dug the bed, let it settle for weeks, or tread it. Then heel each plant in hard — tug a leaf afterwards and the leaf should tear before the plant moves.
2. Plant deep enough to be stable.Set transplants with the lowest leaves at soil level, deeper than they were in the pot. It gives the tall stem a better anchor for the winter.
3. Space them properly.Around 60–75cm each way. Sprouts are big plants standing for most of a year, and crowding produces tall, drawn, unstable plants with poor buttons.
4. Stake or earth up on exposed sites.A mature sprout plant is a metre tall and catches a lot of wind. A cane and a tie, plus soil drawn up round the base in autumn, prevents the rocking that loosens the roots and blows the buttons.
5. Stop feeding nitrogen after midsummer.Nitrogen drives soft leafy growth. Sprouts need a steady, moderate supply early and none late — a high-nitrogen autumn feed is a reliable way to produce blown buttons.
6. Water steadily rather than in bursts.A dry spell followed by heavy rain produces a growth surge that pushes buttons open. Mulching evens it out.
7. Consider removing the growing tip in early autumn.Taking out the top rosette once the lowest buttons are pea-sized stops upward growth and evens the sprouts up, which is useful if you want them all at once. Leave it on if you want to pick from the bottom up over months.
8. Pick from the bottom upwards.The lowest buttons mature first. Snap them off downwards and take the yellowing leaves below at the same time to improve airflow.
9. Choose an F1 variety if this happens every year.Modern F1 sprouts are bred for uniform tight buttons and are markedly less prone to blowing than older open-pollinated types.

Tips

• The top rosette of a sprout plant is excellent eating in its own right — cook it like a small cabbage.
• Blown sprouts are perfectly good food, just loose. Shred them and fry or roast rather than trying to serve them whole.
• Frost genuinely improves the flavour, so sprouts picked after the first hard frosts are sweeter — which is why they are a Christmas crop.
• Sprouts are a long crop, in the ground from spring to the following spring. Plan the rotation around that rather than trying to squeeze another crop in.
• Mealy cabbage aphid is the pest that most often ruins sprouts — it gets down inside the buttons where nothing can reach it, so catching it early on the leaves matters.

Common mistakes

• Planting into freshly dug fluffy soil — The plant settles and rocks all winter, the roots break, and the buttons blow open.
• Feeding a general fertiliser in autumn to 'help them fill' — Late nitrogen produces exactly the soft fast growth that blows buttons. Feed early or not at all.
• Removing the growing tip too early — It stops the plant building the stem it needs. Wait until the lowest buttons are well formed.
• Picking from the top down — The top buttons are the youngest and smallest. Work from the bottom up and the plant keeps producing.

Questions people ask