Microgreens are young vegetable and herb seedlings harvested soon after their first leaves appear. They let you grow something edible indoors without an allotment, a greenhouse or a deep planter. A shallow tray on a bright windowsill can supply fresh shoots for salads, sandwiches and garnishes in around one to three weeks, depending on the crop and growing conditions.
The method is simple, but successful microgreens need clean equipment, suitable seed, light and careful watering. Constantly wet compost and overcrowded seedlings are common reasons a promising tray develops mould instead of a usable crop.
What exactly are microgreens?
Microgreens are not a special species of plant. They are ordinary edible crops harvested very young, generally after the seed leaves have opened and as the first true leaves begin to develop.
They are different from sprouts. Sprouts are often grown without compost and eaten with their roots; microgreens are usually grown in a shallow medium and cut above the compost. Growing methods and food-hygiene considerations differ.
Cress, radish, mustard, beetroot, chard and some salad leaves can work well. Flavours vary dramatically, from mild and leafy to distinctly peppery. Start with one or two types so you learn their growing speed before experimenting with complicated mixtures.
Choose seeds intended for edible microgreens
Buy seeds specifically sold for microgreens or from a reputable supplier that confirms their suitability for edible young shoots. Untreated seed is important; ordinary decorative or treated agricultural seed may not be intended for eating at the seedling stage.
Avoid seeds from plants with poisonous leaves or seedlings. Tomato and potato seeds, for example, are not suitable microgreen crops. When uncertain, check a trusted edible-crop reference instead of assuming every garden seedling is safe.
Equipment for your first microgreen tray
You need a shallow, clean container, seeds, peat-free seed compost and a way to water gently. A reused fruit punnet works if it is thoroughly cleaned and has drainage holes.
Put the growing tray on a waterproof saucer or another suitable catchment tray so excess water doesn't damage your windowsill. Avoid using a deep sealed tub without drainage; water collecting at the bottom can cause root problems.
A plant label is useful if you make more than one sowing. Write the crop and date so you know whether slow progress is normal or a sign that the growing conditions need adjusting.
Preparing the compost
Fill the tray with a shallow layer of clean peat-free seed compost, gently levelling its surface. A fine-textured mix makes it easier for small seeds to establish than compost full of large woody pieces.
Moisten the compost before sowing so you don't have to blast the seeds across the tray with a watering can afterwards. It should feel damp, not saturated.
The Royal Horticultural Society suggests sieving ordinary multipurpose compost if necessary and using a fine-rose watering can to avoid disturbing tiny seeds. Use fresh material rather than compost that has held diseased plants.
How to sow microgreens
Scatter seeds evenly over the compost surface. You can sow more densely than you would for plants intended to mature into vegetables, because you will harvest the seedlings before they need much root space.
However, don't pile seeds several layers deep. Severe overcrowding traps moisture and reduces airflow, increasing the chance of mould and uneven growth.
Cover lightly with compost as directed for the crop. Very small seeds may need only a fine covering, while larger seeds have different requirements. Follow the packet's instructions rather than using the same depth for every variety.
Label the tray, water gently if needed and set it in a warm, bright location.
Light and temperature indoors
Most microgreens do well in a bright indoor position where the seedlings receive enough light to stay reasonably compact. A windowsill may work, but avoid cold glass, radiators and harsh midday sun that dries compost rapidly.
Light becomes especially important after germination. Seeds started in a temporarily dark place should be moved into good light promptly when shoots appear, following the crop's requirements.
Pale, elongated seedlings stretching towards a distant window usually need more light. Increasing fertiliser will not correct that.
How often should you water microgreens?
Keep the growing medium lightly and evenly moist. The seedlings have small roots and can wilt quickly if a shallow tray dries completely.
At the same time, constant waterlogging encourages mould and damping-off diseases. Check the compost rather than pouring water on by habit. A fine spray or gentle watering at the surface works when seeds are first sown.
Once roots establish, some growers water from below, adding a small amount to the catchment tray and allowing it to soak upwards. Remove excess water after the compost has absorbed enough.
Use clean water and avoid splashing soil onto leaves just before harvest.
How long before microgreens are ready?
Many common varieties produce usable shoots within one to three weeks, depending on warmth, light and seed type. Radish and cress may be quick, while some other crops take longer.
Look for opened seed leaves and the first small true leaves, rather than relying entirely on a calendar date. A tray grown on a bright summer windowsill may mature faster than one grown in the middle of a dim British winter.
Taste a small, clean sample from a confirmed edible crop to judge flavour. Microgreens can change in texture and intensity as they develop.
How to harvest without soil in the food
Use clean kitchen scissors to cut the shoots above the compost surface. Hold a small bunch gently and cut without scraping the roots or soil into your harvest.
Wash harvested shoots under clean running water, handle them with clean hands and use them promptly. Keep them refrigerated if you are not eating them immediately.
Microgreens are often eaten raw, so hygiene matters. Discard trays with obvious mould, slimy growth or an unpleasant smell. Don't try to make a mouldy crop safe simply by rinsing it.
Most microgreen trays are treated as one-cut crops. After harvesting, clear the spent roots and compost, wash the container thoroughly and start again with fresh material.
Why is mould growing in my tray?
Visible fuzzy growth may be mould, particularly if compost smells musty and stems are collapsing. Excessive watering, poor ventilation and seed packed too densely can contribute.
Some seedlings produce fine white root hairs near their bases that can resemble mould at first glance. If you're unsure, err on the side of caution with an edible crop.
Improve air movement, avoid leaving trays saturated and clean all equipment before another sowing. Don't reuse diseased compost for food-growing seedlings.
Other common problems
Patchy germination: Seed age, uneven moisture or different sowing depths may be responsible.
Seedlings collapse at soil level: Damping-off diseases can develop in overly wet conditions. Discard affected trays and clean everything.
Leaves turn pale: Check light, waterlogging and whether the crop is naturally pale at that stage.
Seeds stick to leaves: Some seed husks remain attached briefly. Allow normal growth and avoid roughly pulling them off.
Tray dries out overnight: Use a slightly deeper compost layer or choose a position away from intense radiator heat.
Growing a continuous supply
Instead of sowing five trays at once, start a small tray every few days or each week according to your household's appetite. This spreads harvests so you have fresh shoots when you need them.
Try radish for peppery flavour and cress for a fast first crop. Keep notes on how long they take in your particular window. Once the routine works, experiment with other confirmed edible microgreen varieties.
Source
Royal Horticultural Society: Growing microgreens.