How to grow cress

On a windowsill, whenever you like. Cress doesn't care about the season indoors: it germinates in a few days and is ready to cut within one to two weeks. In the darkest winter weeks it grows a little slower and leggier, but it still works.

Outdoors, you can sow from March, once the soil is workable, until September. The best results come from spring (March to May) and late summer (August and September). Cress is a cool-season plant: in hot, dry summer weather and long days it rushes into flower within a couple of weeks, and the leaves turn sharp and tough. If you sow in June or July, choose a spot in light shade and keep it well watered.

Because it is over so fast, sow little and often. A new tray every week or so on the windowsill, and a short row every two to three weeks in the bed, gives a steady supply.

You need a shallow dish, something to hold moisture and seed. Cotton wool or a few layers of kitchen paper are the classic choice; a centimetre or two of seed compost works just as well and gives slightly sturdier plants. Wet the base thoroughly and pour off any standing water.

Scatter the seed thickly, so the seeds almost touch, and press it on lightly. There's no need to cover it: cress germinates in light or dark, and on paper or wool it simply sits on top. After a day the seeds swell and turn slimy, which is normal and helps them cling to the base.

Keep the base moist but not swimming, and put the dish somewhere bright at room temperature. A spray bottle is handy for the first days. At about 68°F you'll see sprouts after two to four days, and the cress is ready to cut in about seven to fourteen days, once it stands 2–3 in tall with open green seed leaves.

Cut it with scissors just above the base. Cress grown this way doesn't regrow usefully, so start the next dish a few days before the current one is ready.

Cress isn't fussy about soil, as long as it stays moist. Rake the bed to a fine surface; it doesn't need compost or feed for such a short crop. A spot in full sun is fine in spring and autumn, while in summer light shade keeps it from bolting.

Sow thickly in shallow drills 4–6 in apart, or broadcast a small patch. Press the seed onto the soil or cover it only very thinly, at most 0.2 in. Unlike most crops, cut cress doesn't need thinning: a dense stand is exactly what you want.

In a 120 × 80 cm raised bed, rows 4–6 in apart run five to seven deep across the width. You'll rarely want the whole bed of it, though. One or two short rows every couple of weeks feed a household, and cress is handy for filling a gap between slower crops.

The seed germinates even in cool soil, from about 41°F, but gets going much faster in warmth: around 68°F it is up in about four days. Early sowings in March can take a week or two to emerge.

Cress has one real need: water. Never let the soil or the cotton wool dry out, or it toughens and bolts. Moist soil also makes life harder for flea beetles outdoors.

Outdoors, cress is ready two to three weeks after sowing, at about 2–4 in tall. Cut it just above the ground, or pick young leaves as you need them. Harvest before the plants flower: once the small white flowers open, the leaves turn hot and tough. Full-grown plants are also much coarser and feathery-leaved, a quite different thing from the tender seedlings.

Cress is best eaten the moment you cut it, and there's no need to wash windowsill cress. Its sharp flavour fades quickly once cut, so cut only what you need.

Garden cress comes as plain (single-leaved), broad-leaved and curled types. Broad-leaved cress gives a little more to eat per plant, curled cress looks pretty on a plate; all are grown the same way.

Watercress (Nasturtium officinale) is a different plant: a perennial that grows in clean, flowing water and is grown commercially in shallow water beds. It can be kept in a pot standing in water, but it isn't a windowsill seed crop. Don't eat wild watercress raw from streams in grazing land, as it can carry parasites; stick to cultivated plants.

Land cress (Barbarea verna), sold in German-speaking countries as Barbarakraut or Winterkresse, tastes much like watercress but grows in ordinary garden soil. Sown in late summer, it is hardy enough to give leaves through mild winters.

Flea beetles are the main pest outdoors. These tiny black beetles jump when disturbed and pepper the leaves with small holes. They are worst in warm, dry weather, from spring on. Keep the soil moist, sow when the weather is cool, and in bad years cover the row with fine insect mesh (about 0.8 mm).

On the windowsill, the most common worry is 'mould' that turns out to be root hairs. Young cress grows a fine, even, white fuzz around its roots, most visible when the base is drying out; it collapses when you water and smells fresh. Real mould grows in patches, may be grey or green, and smells musty. If it's mould, throw the batch away, wash the dish, and next time use less water and more air.

Outdoors, white rust can occasionally show as white, blister-like spots on the leaves. Since you cut cress young, it rarely matters; don't use the affected leaves and sow the next batch elsewhere.

Cress is a crucifer, in the same family as cabbages, radishes, rocket and mustard. It shares their pests and their soil disease, clubroot, which can stay in the ground for up to ten years. Treat cress as a brassica in your rotation: don't sow cress after cress, and give the bed three to four years, at the very least two, before brassicas return.

Planting tables sometimes pair cress with radishes and claim it improves their flavour. We found nothing beyond tradition for that. Because cress is cut within weeks, it hardly competes with anything and is easy to tuck between slower crops.

Two real points: cress shares flea beetles with radishes, rocket and young cabbages, so a row next to them can draw the same pests; and it belongs in the brassica slot of your rotation. Its one proven talent is as a test plant: gardeners sow cress on fresh compost to check it is mature enough, because the seedlings react quickly to anything harmful.