Why microgreens love a kitchen windowsill

Microgreens are the young shoots of vegetables, herbs and salad crops, harvested just as the first pair of seed leaves opens — and sometimes a little beyond. Because you eat them at that stage, you never need the deep soil, large pots or long growing season that full-sized plants demand. A tray the depth of a paperback is ample. The roots stay shallow, the plants can be packed in tightly, and most crops are ready in seven to twenty-one days.

The kitchen windowsill suits them for two further reasons. Gentle indoor warmth speeds up germination, so seeds that sulk outdoors in a cold October romp away on a sill. And the light, even from a north-facing window, is enough to keep shoots green and tender, provided you give them as much of it as you can. A sunny south-facing sill will grow bigger, tougher leaves faster — useful for pea shoots, less so for delicate basil.

What you need to start

You can spend very little, because most of the kit is already in the kitchen.

• Shallow trays: purpose-made seed trays with drainage holes, or recycled mushroom punnets, foil roasting trays or the base of a large tub. Aim for two to five centimetres deep and pierce holes if there are none.
• A cover: cling film, a plate, or a second tray upturned on top. This creates the dark, humid spell that seeds germinate best in.
• Compost: a light seed-raising mix or coir is ideal. Ordinary multi-purpose compost works if you rub out the lumps and avoid pressing it down hard.
• Seeds: buy in bulk where you can, because you will sow thickly. Reliable first crops are radish, mustard, cress, broccoli, kale, peas and sunflower.
• A spray bottle and a small saucer for misting and for bottom watering.

Sowing thickly, step by step

The whole method rests on density. Sparse sowing wastes space and gives you a few straggly stems; thick sowing gives you a lush, self-supporting carpet that is easy to cut.

• Fill the tray to within a centimetre of the rim, level the surface and firm it gently with your palm. Water the compost before sowing so you are not washing seeds around afterwards.
• Scatter seed evenly and generously. Radish and mustard want roughly a seed every half centimetre. Peas and sunflower want a single layer with the grains almost touching, so pre-soak them overnight to speed things up.
• Cover most seeds with a fine layer of compost or vermiculite — roughly two to three times the seed's own thickness. Mustard and cress can be left uncovered, but mist them well and keep the cover on longer.
• Press the surface lightly so every seed makes contact with the damp compost, then cover the tray and put it somewhere warm and dark at around 18–21°C. A cupboard or the top of the fridge is fine.
• Check daily. The moment you see green, remove the cover and move the tray into the light. Leaving it covered any longer invites mould and weak, yellow stems.

Watering, light and airflow

Once the shoots are up, water from below. Stand the tray in a centimetre of water for a few minutes, then lift it out and let it drain — this keeps the leaves dry and discourages damping off. If the surface looks dry between waterings, mist it lightly rather than pouring.

Light matters more than most people expect. A windowsill that reads as bright to your eye can still be dim to a seedling, so rotate the tray a quarter turn each day to stop the shoots leaning hard towards the glass. In high summer, shield them from fierce midday sun with a sheet of kitchen paper, as glass can scorch tender leaves in an hour.

Airflow is the other quiet essential. A window cracked open for part of the day, or a fan on its lowest setting nearby, keeps the humid microclimate from turning stale. Damp, still air is the main cause of mould on a windowsill crop. Aim for a steady 15–21°C; a cold sill in winter will slow everything down, so lift trays onto a folded tea towel at night if the glass gets chilly.

Harvesting and using your crop

Cut when the shoots are at their tender best rather than waiting for size. Radish, mustard and broccoli are ready at about five to seven centimetres, peas at eight to twelve, sunflower once the seed cases have dropped and the stems stand upright. If the stems feel wiry or the leaves leathery, you have left them a day or two too long.

Use sharp scissors and cut just above the compost line, taking the whole tray in one sweep. Some crops — peas, coriander and kale in particular — will push up a smaller second flush if you keep watering, but the second cut is always thinner than the first.

Eat them straight away for the best flavour. Rinse briefly in cold water, dry on kitchen paper, and pile onto sandwiches, fold through salads, stir into soups at the last moment or scatter over eggs. Pea shoots and sunflower make a fine substitute for basil in a green pesto. Anything you cannot use within the hour keeps for three or four days in a lidded tub lined with kitchen paper in the fridge.

Troubleshooting and keeping a steady supply

• Mould or fuzzy white patches: usually too wet, too warm or too enclosed. Remove affected patches, increase airflow, water less often and sow slightly thinner next time.
• Pale, leggy stems: not enough light after germination. Move the tray to a brighter sill immediately, though do not expect them to thicken up much.
• Slow or patchy germination: a cold windowsill or dry compost. Pre-soak larger seeds and keep the tray consistently moist, never sodden.
• Continuous harvests: sow a fresh tray every four or five days rather than one big tray a fortnight. Three or four small trays on rotation will keep you in salad leaves all year, even in a flat with a single window.