Growing Microgreens at Home in Scotland

Look at the tray on your windowsill. If the seedlings are pale, thin and flopping sideways, they are stretching for light they are not getting. If there is a fuzzy white haze on the mat, do not reach for the bin yet: fine white fluff around the base of each seedling is usually root hairs, which are harmless, and a grey, patchy, musty-smelling growth that spreads over stems is mould, which is not. Telling those two apart, and getting enough light onto the tray, come first.

What microgreens are, and what they are not

Microgreens are seedlings of familiar vegetables such as cress, radish or beetroot, sown densely and cut very young, once the first true leaves appear. True leaves are the second set, the ones that look like the adult plant; the first pair to open are the plain seed leaves. You eat the stem and leaves and leave the root and seed husk behind in the tray.

Sprouts are a different product. Sprouting seeds such as mung bean or alfalfa are kept wet, warm and usually dark in a jar, with no growing medium, and are eaten whole, seed and root included. That warm, wet, unlit method is why sprouts are handled as a higher food-safety risk than other salad crops. After a 2011 E. coli outbreak in Europe linked to sprouts grown from contaminated seed, Food Standards Scotland tested soaking and washing treatments on contaminated mung bean and alfalfa seed and still found low levels of contamination once the seeds had sprouted. Guidance for pregnant women from NHS inform is that sprouted seeds should be cooked until hot throughout. Do not follow this tray method for jar sprouting.

A tray of microgreens grown in light on a clean medium and cut above the surface is much closer to growing cress. The risks that remain are contaminated seed, dirty medium and a tray that stays wet.

For where microgreens sit among other indoor crops, see the windowsill crops guide.

Choosing seed

Buy seed sold for sprouting or microgreens, or plain packets of the crop itself that carry no dressing or coating. Do not use seed sold in bulk for field sowing or seed that has been treated with a coloured dressing (a pink, blue or green powdery coat on the seed), since those are not intended to be eaten as shoots. This is the one place where cheap is a false economy.

Suitable crops include cress, radish, chard, turnip, mustard and beetroot, along with coriander, fenugreek, purple basil, Greek cress, amaranth, red-stemmed radish and brassicasThe cabbage family: cabbage, kale, broccoli, cauliflower, Brussels sprouts, kohlrabi, swede, turnip and more, sharing the same pests, diseases and rotation rules. Full definition → generally. Stick to crops known to be eaten as shoots; not every vegetable seedling is safe to eat, so do not grow tomato, potato or aubergine this way.

Radish, cress and mustard finish quickly enough that a failed tray costs you little. Beetroot and chard seeds are clusters, so they come up unevenly and take longer. Taste a few stems at each stage, because the flavour builds as the plants grow. Your own taste, not a day count, tells you when to cut.

Growing medium

You have two sensible options.

Peat-free compost. Fine peat-free seed compost, or multi-purpose compost sieved to remove lumps, in a container about 5cm deep. Moisten it, firm it lightly and level it. This gives a sturdier crop. The peat-free compost guide explains what to buy. Fresh commercial compost is the safer choice; garden soil or a bag left open for months is not.

Kitchen roll, felt or hemp mats. Cut to fit the tray, wet, and scatter seed on top. Cheap, clean and tidy, and good for cress and fenugreek. The weakness is that the mat holds only so much water and dries fast in a heated room, so it needs checking daily. If you want to go fully soilless, the Kratky method guide and the hydroponics for beginners guide cover water-based systems.

Whichever you use, clean the tray first. If you are reusing compost or trays, the guide to sterilising compost for seed starting explains how, and a tray that has had a damping offA fungal disease that kills seedlings at soil level, usually caused by overwatering, poor airflow, or reused unsterilised compost or trays. Full definition → problem should be washed and disinfected before it is used again.

Setting up the tray

Any shallow container with drainage works: a purpose-made seed tray, a takeaway tub with holes punched in the base, or a cake tin. You need a second tray or saucer underneath, which is what you will water into.

1. Fill with moist compost about 5cm deep and firm it gently, or lay a wet mat.
2. Sprinkle the seed evenly over the surface. Aim for seed almost touching, but not piled in clumps.
3. Cover compost-grown seed with a very thin layer of compost. Press mat-grown seed down lightly.
4. Mist to settle the seed, then cover the tray with another tray, a plate or a sheet of card.
5. Set it somewhere the air is mild, around 18 to 22°C (see below).

Dense sowing is the point of microgreens, but thick clumps with no air between them invite damping off. Aim for even cover with no piles, and if grey patches appear in the thickest corner of a tray, sow thinner there next time.

Temperature matters for germinationA seed sprouting: breaking dormancy and putting out its first root and shoot, given the right warmth and moisture. Full definition →. 18 to 22°C is ideal, which is a normal living room but often not a cold north-facing sill or a porch. If your sill is chilly, germinate on a warmer shelf and move the tray to the light afterwards. The seed germination temperature guide has the detail.

Blackout, then light

Blackout means keeping the tray covered and dark. Covering the tray for the first few days keeps the seed dark and damp while it germinates and pushes the stems to lift the cover, which gives you a sturdier plant. When the seedlings lift the cover or reach it, take it off and move the tray into full light. Check daily from day two: a lid left on too long gives pale, yellow, spindly growth. Pale stems from the covered days turn green once they are in the light. If the cover holds moisture, lift it briefly each day to let air out.

Some growers skip the cover and put sown trays straight on a bright sill. A cover suits larger seed such as radish and helps a tray that would otherwise dry out on a radiator shelf.

How much light is enough

Microgreens grow best on a windowsill that gets at least four hours of natural light a day. A north-facing sill in a Scottish winter can struggle to deliver that, so expect slower growth and paler leaves, and a few extra days to harvest compared with summer.

Stems that lengthen and pale while leaning hard towards the glass mean too little light. The leggy seedlings guide covers the cause and cure in more detail, and the day length and photoperiod guide explains what plants actually respond to.

A grow light is worth adding when your best sill is not bright enough, or you want reliable trays from December to February. A small LED strip on a timer is enough for a tray; the LED grow lights guide has the spectrum, wattage and running costs. Keep the light a short distance above the tray and raise it as the seedlings grow. On a plain sill, turn the tray a half-turn each day so the seedlings do not lean, and stand a sheet of white card behind it to bounce light back.

Watering without mould

Wet, still air is what mould wants.

• Mist or bottom water. Mist to settle the seed, since heavier watering can dislodge seed and stems. Bottom watering, where you pour water into the lower tray and let the medium draw it up, keeps the leaves and stems dry. Tip out any water still standing in the lower tray once the medium has drawn what it needs.
• Keep the medium moist, not soggy.
• Use mains water for seedlings in trays.
• Keep air moving. Damping off is the fungal collapse of seedlings, and it thrives in crowded, humid, still air, so ventilate to reduce humidity. A tray in the corner of a shut room, especially with a lid on, is exactly that.

Heated rooms in winter create two opposite problems. A tray on a windowsill above a radiator dries out quickly, particularly a mat, because heated indoor air is dry. In a long Scottish heating season a tray on a cold sill next to a closed window can sit wet and still, especially where condensation runs down the glass, so keep it off the pane. Neither needs equipment, only attention: feel the medium each morning and open a window for a few minutes, or turn the tray, when the air is stagnant.

Root hairs or mould?

Root hairs are fine, white and cottony, and grow from the roots as they search for water. You see them in the first days, close to the seed and the surface of the mat, and they look like a frost around the base. They are fuzzy but even, they sit against the roots, and they usually flatten or vanish when you mist them, though that test is a rule of thumb rather than a guarantee. They are not a problem.

Mould is different. It looks greyish or dull white, grows in patches that spread over stems, leaves or the mat itself, smells musty or sour, and the seedlings beneath turn soft and collapse. If you see it, do not eat that section, and once it has spread beyond a small patch, bin the tray.

If you are unsure, mist the tray and look again in an hour. If you are still unsure, treat it as mould. Bin the tray, wash and disinfect the container, and put the next tray in a more ventilated spot with thinner sowing.

Harvest

Harvest comes at one to three weeks, once the first true leaves have appeared and the seedlings are sturdy. The fastest crops are ready in as little as seven to 10 days, and winter light adds a few days. Cut with clean scissors just above the surface of the medium, rinse, and use promptly.

Cut when the leaves have opened and the tray looks like a small green lawn; some crops such as radish and cress are often cut a little earlier, at the seed-leaf stage, once they taste right. Waiting longer usually costs flavour and increases the risk of the tray tipping over into mould. Sow a new tray every week or so to keep a supply going.

Realistic yield and cost

Expect a garnish, a sandwich filling and a salad topping, not a salad course. One tray is a modest handful of crop, so to fill a bowl weekly you need two or three staggered trays. Seed is the main cost, then compost, and a light if you add one; the tray can be a container you already own. Cress and radish give the best return for the money.

Food hygiene

• Start with clean hands, a clean tray and fresh compost or a new mat.
• Buy seed from a source that sells it for eating as shoots.
• Wash the crop after cutting and before eating.
• Cut above the medium and do not eat roots, husks or anything from a section with mould.
• If someone who is pregnant, elderly or unwell will eat the crop, take the same care you would with any raw salad.

After the crop

Spent compost is full of fine roots, so it makes a decent addition to a compost heap. The reusing spent compost guide explains what is safe to reuse and what to bin. Do not reuse compost from a tray that had mould, and do not reuse a mat. Spent mats can go in the compost bin, and any containers should be washed before reuse.

For other fast crops beyond microgreens, see the quickest sow-to-harvest crops and the container and patio crops guide.

Common questions

Sources