Blanching

Blanching is the gardener's trick of keeping a vegetable's stems or leaves pale by shutting out the light. Without sunlight, the plant can't make the green pigment chlorophyll, so the covered part stays white or yellow, stays tender, and loses the bitterness that light and weather can bring. It's a finishing technique you apply to plants that are already growing well — not a way to make them grow faster.

The classic UK example is the leek. To get those long white shanks you see in the shops, you gradually pull soil up around the stems as they grow — a process called earthing up. Each centimetre of stem buried becomes pale and sweet. Do it little and often from late summer, keeping soil out of the centre of the plant, and you'll lift leeks with generous white sections by autumn and winter. Some growers slip a cardboard tube or drainpipe collar over each plant instead, which is tidier and keeps grit out of the layers.

Celery and endive are the other crops UK gardeners blanch. Trench celery is blanched by wrapping the stems in cardboard, brown paper or sleeves and earthing up around them through the season; modern self-blanching varieties do most of the job themselves if grown in tight blocks so the plants shade each other. Endive (and its cousin, frisée) is blanched in the last week or two before cutting — cover the heart with a plate, a pot, or by tying the outer leaves over the centre — to take the bitter edge off the leaves.

It's worth not confusing blanching with forcing. Both involve excluding light, but they aim at different things. Forcing — as with rhubarb or chicory — uses darkness and a little warmth to bring a crop on earlier than it would naturally appear, often producing pale, tender shoots out of season. Blanching simply whitens and sweetens stems that are already growing in their normal season; there's no attempt to rush them. In short: forcing is about timing, blanching is about colour and flavour.

One more point of confusion worth clearing up. In the kitchen, "blanching" means something completely different — plunging vegetables into boiling water for a minute, then into cold, usually before freezing. That's a cooking step, not a growing one. The garden sense, covered here, is all about light, not heat.

A few practical tips: only blanch healthy, dry plants, as covered stems sitting in damp can rot. Keep the growing tip and the centre of the plant clear of soil. And don't blanch too far in advance of harvest — pale tissue is soft and won't store as long as green growth, so blanch with a picking date in mind.