Growing Microgreens Indoors Through Winter: A Windowsill Crop That Pays Off in Days

By February, the garden is a memory and the grocery store's greens have traveled further than most people have. This is the season microgreens were made for. They are simply the young seedlings of ordinary vegetables and herbs — radish, broccoli, sunflower, pea — harvested when they are a few inches tall and a week or two old. They taste more intense than their full-grown versions, they grow on a windowsill, and they go from seed to salad in about ten days. For a household that likes fresh food in winter, there is hardly a faster return on a packet of seeds.

The setup is humble on purpose. A shallow tray, some seed-starting mix, seeds, water, and light. No greenhouse, no grow room, no special equipment — though a simple shop light helps on short, grey days. The craft lies in the details: the right seed density, the right moisture, and the discipline to harvest at the right moment.

Start With These Four
Not every seed makes a good microgreen, and a first tray should be a forgiving one. These four are reliable, fast, and distinct enough that a household can learn what it likes:
Radish — the beginner's best friend. Ready in about 6–8 days, with a peppery bite that wakes up sandwiches and soups. Radish seed is cheap, germinates eagerly, and tolerates imperfect light better than most. If only one variety is grown, grow this one first.
Broccoli — the mild workhorse. Ready in about 10–12 days, with a gentle, fresh flavor that suits salads and smoothies. Broccoli microgreens are less spicy than radish and more versatile at the table, which makes them the tray most households reach for daily.
Sunflower — the substantial one. Ready in about 12–14 days, with thick, lemony leaves and a satisfying crunch. Sunflower seeds are larger, so they need a slightly deeper tray and a bit more water, but the harvest feels like a real crop rather than a garnish.
Pea shoots — the sweet one. Ready in about 12–14 days, with tender tendrils and a sweet, fresh-pea flavor. Pea shoots are wonderful wilted into pasta or piled onto toast, and they regrow after a first cutting if the tray is kept watered — a second harvest from the same seeds.
A note on seed sourcing: buy seeds sold for sprouting or microgreens, or untreated garden seed. Seeds treated with fungicides or coatings meant for field planting are not suitable for eating young. Reputable seed sellers label this clearly; when in doubt, ask before buying.

The Setup, in Order

Choose a tray with drainage. A shallow tray about two inches deep works well. Drainage holes matter more than depth — microgreens sitting in standing water rot quickly. A second tray underneath catches drips and keeps the windowsill dry.

Fill with moist seed-starting mix. Use a fine, soilless seed-starting mix rather than heavy garden soil, which compacts and holds too much water. Moisten it before sowing so it is damp like a wrung-out sponge, not wet.

Sow thickly, but not in piles. Scatter the seeds evenly across the surface, denser than garden sowing — seeds nearly touching is right for most varieties. Piles of seed trap moisture and invite mould; gaps waste tray space. A light press with a flat hand or a piece of cardboard settles them into contact with the mix.

Cover for the dark days. Cover the tray with another tray, a lid, or a damp cloth for the first 2–4 days. Darkness encourages strong germination and helps roots anchor. Check daily: the mix should stay damp, not dry and not soggy. A spray bottle gives control that a watering can does not.

Uncover into the light. Once seedlings are about an inch tall and showing their first leaves, move the tray to the brightest windowsill available — a south-facing window is ideal in winter — or under a simple fluorescent or LED shop light kept a few inches above the tray for 12–14 hours a day. Weak light is the most common cause of pale, leggy microgreens; if seedlings stretch tall and flop, they need more light, not more water.

Water from below when possible. Set the tray in a shallow dish of water for a few minutes and let the mix absorb moisture from the bottom, then drain fully. Bottom watering keeps the leaves dry, and dry leaves mean less mould. If watering from above, use a fine spray and water in the morning so leaves dry during the day.

Harvest at the right moment. Most microgreens are ready when they are 2–4 inches tall and have their first true leaves — the second set of leaves, which look like miniature versions of the adult plant's leaves. Cut with clean scissors just above the soil line. Rinse gently, dry, and use the same day for the best flavor, or store in a dry container in the fridge for a few days.

The Mistakes That Ruin a Tray

• Sowing seeds in piles: damp clumps breed mould. Scatter evenly; thin out dense patches before covering.
• Overwatering: soggy mix, rotting stems, mould. Water from below, drain fully, and let the surface dry slightly between waterings.
• Too little light: pale, leggy, weak seedlings. Brightest window, or a shop light a few inches above the tray.
• Harvesting too late: tough, bitter greens. Cut at 2–4 inches, at the first true leaves — not when the tray looks like a lawn.
• Dirty trays: mould and off flavors in the next batch. Wash trays with hot soapy water between batches and let them dry fully.
• Wrong seeds: treated seed, or varieties that grow poorly as microgreens. Buy seed labeled for sprouting/microgreens; avoid treated garden seed.

Keeping a Winter Supply Going
A single tray feeds a household for a few days, not a month. The rhythm that works is a staggered one: sow a new tray every 4–5 days, so that as one tray is harvested, the next is already a few days along. Two or three trays in rotation — one germinating in the dark, one growing in the light, one ready to cut — keep fresh greens on the table all winter with about ten minutes of attention a day.
The cost is small: a bag of seed-starting mix, a few trays, and seed packets that hold dozens of sowings. The return is fresh, living food in the darkest months, grown ten steps from the kitchen table. In a season when the garden sleeps, that is no small thing.

Frequently Asked Questions
Do microgreens need fertilizer? No. The seed itself carries enough energy for the short life of a microgreen, and the seed-starting mix provides what little else is needed. Fertilizer at this stage usually causes more problems — salt buildup, burnt roots — than it solves.
Can I regrow a tray after cutting? Most varieties give one good harvest; pea shoots are the cheerful exception and often regrow for a second cutting. For the rest, compost the used mix, wash the tray, and start fresh — the next tray is only ten days away.

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