Why the Kitchen Windowsill Works So Well

Salad leaves are the most generous crop a small space can give you. They germinate in days, grow fast, and — crucially — they don't need to reach full size before you can eat them. A windowsill that catches four or five hours of daylight is more than enough to raise a tray of tender, peppery leaves, and unlike a garden bed it sits within arm's reach of the chopping board. There is a real pleasure in snipping a handful of rocket straight onto a sandwich while the kettle boils.

The other advantage is speed. Cut-and-come-again varieties are designed to be harvested young and repeatedly, so you're not waiting three months for a single head of lettuce. Start a tray in early spring and you can be picking leaves by Easter, then sowing the next batch before the first one has finished.

What You'll Need

• A shallow tray — roughly 5cm deep and 20cm wide. Proper seed trays are ideal, but mushroom punnets, old takeaway containers and foil roasting tins all work. Poke a few drainage holes in the base if there aren't any.
• Fresh peat-free multipurpose compost. Don't use soil from the garden: it compacts in a shallow tray, drains badly and often carries weed seeds.
• Cut-and-come-again seed. Lettuce, rocket, mizuna, mustard, pak choi, spinach and chard are all reliable. A mixed packet gives you a prettier, tastier tray.
• A mister or a small can with a fine rose. Coarse watering will wash your seed into a corner.
• A saucer to sit the tray on, and a clear lid or a piece of cling film for germination.

Sowing Your First Tray

Fill the tray loosely with compost, then press it down gently with your fingers or the base of a mug so the surface is level but not rock-hard. Aim to leave about 2cm of clear space below the rim, which makes watering far easier.

Water the compost before you sow, using the mister, until it's evenly damp but not dripping. Then scatter the seed thinly across the surface. You're aiming for roughly one seed every centimetre — closer than that and the seedlings compete, which encourages weak, leggy growth and damping off.

Cover the seed with about 3mm of compost or a scattering of vermiculite and mist the surface again. Press the lid or cling film over the top to hold in moisture, then put the tray somewhere warm and bright but out of direct midday sun. Most salad seed germinates in five to ten days. Check daily and remove the cover the moment you see green, or the seedlings will stretch and flop.

Day-to-Day Care

Light is the thing that makes or breaks a windowsill crop. Once the seedlings are up, give them the brightest spot you have — a south- or east-facing sill is ideal. Turn the tray a quarter turn every couple of days so the plants grow upright rather than leaning into the glass.

Watering is a matter of little and often. The compost should feel like a wrung-out sponge: damp to the touch, never sodden. Once the roots have knitted the surface together, you can water from below by pouring a centimetre of water into the saucer and letting the tray drink it up. Empty anything left after an hour, as standing water rots roots.

There's no need to feed the first two crops — the compost has enough in it. After the second cut, a weak dose of seaweed feed every fortnight will keep the leaves coming. If seedlings are crowded, thin them to around 3cm apart by snipping the extras with scissors rather than pulling, which disturbs the roots of the plants you're keeping.

Cutting and Coming Again

This is where the tray earns its keep. Once leaves are around 7–10cm tall, take a pair of sharp scissors and cut them about 2–3cm above the compost, working across the tray rather than stripping one patch. Harvest in the morning if you can, when the leaves are at their crispest.

Water gently after each cut and the plants will push up a second flush within a fortnight, then a third. Most trays give three or four good harvests before the plants exhaust themselves. Don't let them grow too large: big, old leaves turn bitter, especially rocket and mustard, and lettuce will bolt — running to seed and turning tough — in warm weather. If you have a sunny windowsill in midsummer, move the tray a little further from the glass during the hottest part of the day.

Sowing Little and Often

The secret to an uninterrupted supply is succession. Instead of filling one tray, sow a small tray every two to three weeks from February through to September. Each sowing takes two minutes and costs pennies. In winter, growth slows dramatically and light levels drop, so expect thin pickings; a bright sill will still give you something, but spring onwards is when the tray really comes into its own.

If seedlings suddenly collapse at the base, you're almost certainly watering too much and keeping the air still — ease off, remove any lid or cover, and improve ventilation. Pale, spindly plants mean too little light. Both problems are easy to fix, and there is always another tray to sow.