Growing Microgreens in a Greenhouse

11.08.2026.

The growing principle

Not miniature vegetables, but short, disciplined crop cycles.

Microgreens are edible young plants harvested after germination, once their cotyledons have opened—depending on the crop and preferred cut, just before or as the first true leaves begin. Unlike sprouts, they usually grow on a shallow substrate or suitable growing mat. Cut just above the surface; seed hulls, roots and growing medium remain in the tray.

This distinction determines how the greenhouse should be used. A tomato bench benefits from space, warmth and a long season. A microgreen bench benefits chiefly from repeatability. The cycle from dry seed to harvest is so brief that small errors quickly show: an over-sown tray stays wet, a pleasant greenhouse in the morning can become very hot by afternoon, and dirty scissors can compromise an otherwise carefully managed batch.

For keen home growers, this precision is useful rather than intimidating. You need neither a large installation nor a complicated feeding programme to begin. A dependable tray format, a few straightforward crops, drinking water, an easy-clean work surface and a daily check at roughly the same time matter most. Treat the first month as calibration. Record the crop, seed batch, sowing weight, any soaking time, covering time, start of the light phase and condition at harvest. These notes are more valuable than a supposedly universal harvest day.

Microgreen quality is set before sowing—and protected until chilling.

01 / Seed behaviour

Choose by rhythm, not colour alone.

Start with a crop whose seed size and germination behaviour can be assessed clearly in one tray. Fine brassica seed quickly forms a low, compact canopy. Larger peas and sunflowers produce more substantial shoots, but need more room, closer water management and consistent cleaning. Avoid mixtures at first. Only once you know how quickly each type germinates, how much water it absorbs and when it becomes too tall or firm for your taste can harvests be sensibly combined.

Buy clearly labelled, untreated seed specifically intended for eating as sprouts or microgreens. Keep details of the supplier, germination rate and batch, and label every tray with crop and sowing date. This helps isolate a weak run, repeat a successful process and identify whether a batch grows more slowly than usual during a cool or overcast greenhouse week.

Fine seed / quick

Broccoli

Soaking: Usually unnecessary.
Dark phase: Short and controlled.
Character: Mild, fresh and delicately savoury.
First tray: Ideal for practising even sowing.

Fine seed / colourful

Radish

Soaking: Usually unnecessary.
Dark phase: Short; uncover once seedlings straighten.
Character: Peppery, crisp and colourful.
First tray: Beginner-friendly; still monitor density.

Large seed / vigorous

Pea shoots

Soaking: Often useful; drain thoroughly afterwards.
Dark phase: Light covering can aid rooting.
Character: Sweet, juicy and generous.
First tray: Easy to read, but needs airflow.

Large seed / robust

Sunflower

Soaking: Commonly used, with clean drinking water only.
Dark phase: Remove the cover promptly as growth increases.
Character: Nutty, crisp and full-bodied.
First tray: Best once your hygiene routine is secure.

Use only untreated seed intended for growing and eating as microgreens or sprouts. Treated, coated or ornamental seed does not belong on a microgreen bench. At first, grow one species per tray and mix different crops only after harvest, when their cutting times and growth patterns are known.

02 / Density as a variable

Dense enough for a canopy. Open enough to breathe.

Too sparse

Productive density

Overcrowded

Seed should form an approximately even surface, not mounds beside bare patches. In a productive tray, cotyledons close into a harvestable canopy while individual stems can still dry after watering. Where seeds lie in thick lines or clumps, moisture remains trapped at the surface. Weak, stretched stems and uneven growth then become more likely.

Tray, medium and calculation

Measure once. Record the result consistently.

A shallow tray of around 30 × 50 cm is practical for home greenhouse growing: differences in density and germination are easy to see while the tray remains manageable. A solid lower tray beneath a perforated growing insert enables simple bottom watering. The lower tray is a temporary reservoir, not a permanently filled water basin.

Starting seed quantity = tray area × proven crop rate.

There is no universal gram amount per tray. Seed size, variety, germination, medium, light level and desired harvest stage all change the appropriate quantity. Begin with your microgreen seed supplier’s guidance, weigh every sowing with kitchen scales and adjust only after comparing canopy closure, surface dryness and harvest appearance. New seed batches deserve their own test tray first.

Suitable media include fresh, light, structurally stable seed compost without raw animal manures, coconut-fibre products from a reliable source, or mats specifically intended for this crop. Moisten the medium evenly before sowing without soaking it. Dense garden soil is unsuitable for this shallow, short-term crop. Also avoid immature compost and materials of unknown origin, as microgreens are often eaten raw.

03 / Tray setup

Keep roots, water and the edible canopy functionally separate.

Keep the system simple enough to clean completely after every batch. Moisture reaches roots from below; between waterings, the edible leaf canopy stays as dry and well ventilated as possible.

Air around the canopy

Even sowing zone

Root mat and medium

Perforated insert

Lower water reservoir

Place a perforated growing insert inside a solid lower tray. This lets the medium take up water from below, while surplus water can be poured away afterwards. Keep the substrate layer shallow, level and evenly moist. Spread seed as a calm, even layer rather than in heaps. Roots anchor in the medium; enough open space must remain around the leaves for the crop to dry between waterings.

Food-safe contact surfaces Use intact, washable trays and reserve them for edible crops. Cracked containers can retain residues and cannot be cleaned reliably.

Medium depth A thin, level layer is sufficient for many quick-growing microgreens. Peas and sunflowers usually need more support than finely sown brassicas.

Water route Add water to the lower tray, let it rise into the root zone and remove excess. Inserts should not stand with submerged roots for extended periods.

Air route Leave visible space around every tray. Air needs to circulate above and between trays, not merely move somewhere in the greenhouse.

04 / From dark to light

The dark phase is a germination tool, not a fixed ritual.

Some crops benefit during early germination from a second tray as a cover, a dome or a light weight. The aim is even moisture and good contact with the medium—not a standard number of dark days. Crop, temperature and seed vigour decide when the cover comes off.

Phase 01

Sow and settle

Even sowing

Phase 02

Rooting

Check daily

Phase 03

Move into light

Filtered daylight

Phase 04

Finish with airflow

Dry and upright

Level the moist medium, distribute seed evenly and press only enough for contact. Mist only if it settles the seed; avoid puddles.

Check the tray every day. If roots lift the insert or seedlings press firmly against the cover, reduce the weight or uncover them. Warm, stagnant air and an unusual smell are warning signs.

Move trays into bright but tempered greenhouse light as cotyledons are ready to open. Avoid an abrupt move into hot, direct midday sun behind glazing.

Water from below as needed, ventilate the greenhouse and harvest when the crop is crisp, proportionately grown and at its intended stage.

Watch for warning signs: A tray with a musty or sour smell, fluffy growth, a constantly wet surface, slime or plants collapsing in patches should not be continued or harvested. Separate and discard a suspect batch, clean the surrounding area and review sowing density, water quantity, temperature and air movement before sowing again. Washing cannot make a questionable crop safe afterwards.

05 / Greenhouse management

Give the quickest crop the calmest place in the greenhouse.

Greenhouse growing is efficient because daylight, water, tools and the harvest route can sit close together. It also creates the key risk for microgreens: temperature and humidity rise rapidly in an enclosed glazed structure. The aim is not maximum warmth. Seek an even, moderate environment where the canopy dries quickly without heat build-up or direct sun stress.

For many common crops, a moderately warm range of around 18 to 24 °C is a useful starting point. A thermometer at tray height is more helpful than judging conditions at the door. Check the climate at the brightest time of day, not only on a cool morning. After a cold night followed by sunshine, open roof vents and the door early. In South African spring, sunny days can heat shallow trays sharply. In summer, a shaded bench or light shade cloth is often more effective than extra water, because watering does not solve heat stress.

Natural light may be sufficient for robust, fast-growing crops in South Africa’s cooler seasons if the site is open and glazing is clean. During darker winter periods or long spells of cloud, safely installed plant lighting can extend the day; more warmth does not replace missing light. A small circulating fan should move air gently around trays without continually drying one edge. Avoid condensation drips, cold draughts at the door and dead corners behind stored pots.

Classic aluminium greenhouse

Store
seed

Prepare
sowing

Manage
crop

Cut +
chill

Organise the greenhouse bench like a small food station.

Leave at least a hand-width of clear space beside trays, keep hose ends and watering nozzles off the ground, and reserve a clean surface for scissors, labels and empty harvest containers. The flexible interior of a Classic aluminium greenhouse can be arranged as a compact, orderly growing studio. Use that flexibility for washable surfaces, airflow, seasonal shading and short work routes instead of squeezing another tray into a crowded corner. A bench is productive when each insert can be checked, watered and cut without moving unrelated garden equipment, and the whole area can then be cleaned thoroughly.

06 / Food safety

Work consistently forwards: dirty steps never return to harvest.

Microgreens are often eaten raw. Cleanliness is therefore part of crop management, not an optional finishing step. Buy untreated seed specifically suitable for eating as sprouts or microgreens, and use drinking water for soaking, watering and, if needed, washing. Wash hands before handling seed or cut produce. Animals, dirty garden tools, raw animal manures and immature compost do not belong in the production and harvest area.

Cleaning and sanitising are separate steps. First remove soil, roots and visible residues with water and a suitable cleaner. Only on a clean surface can a sanitising step suitable for food contact work effectively when used according to the manufacturer’s instructions. Establish a simple end-of-cycle routine: empty the tray, remove the root mat, clean trays and tools, rinse as directed, sanitise where appropriate, air-dry and store away from substrate, hoses and garden shoes.

Stop: Used trays, hose ends, substrate residues and garden shoes must not enter the cutting, packing and chilling area.

01Receive

02Clean

03Sow

04Grow

05Cut and chill

Store seed dry, labelled and separate from crop-protection products or other chemicals. Clean trays, tools and bench surfaces before food contact. Handle substrate and seed in a defined sowing area. During cultivation, water carefully from below and remove waste promptly. At harvest, use clean, sharp cutting tools and suitable containers; then refrigerate microgreens without unnecessary delay. The direction remains clear: substrate work and used trays never cross back into the clean cutting and packing area.

07 / Cutting window

Harvest by condition, not a calendar promise.

Times such as seven, ten or fourteen days are only guides. Light, temperature, variety, seed batch and desired stem length alter the real harvest time. Look for an upright, evenly coloured canopy, fully opened cotyledons, clean dry surfaces and a fresh crop-typical flavour. Cut during the cooler part of the day where possible, before substantial heat builds beneath the glazing.

Use clean, sharp scissors or a knife and cut just above the medium. A clear distance from the surface reduces substrate residues and prevents harvested material being pulled through soil or fibres. Clean, dry-harvested microgreens do not automatically need washing; extra moisture can shorten storage life. If washing is needed for the kitchen, use drinking water and dry leaves very thoroughly before chilling.

Harvest only what can be eaten, shared or packed in prime condition. Small staggered sowings—such as one or two trays a few days apart—usually supply a household more reliably with fresh produce than one large sowing where every tray reaches cutting stage together.

Radish

Crisp cotyledons

Broccoli

Even canopy

Pea

Tender shoots

Sunflower

Strong leaf pair

Radish tastes best with open, crisp cotyledons and its distinctive peppery note. Cut broccoli when the canopy is tender and evenly green. With pea shoots, decide your preferred stem length before plants become firmer. Harvest sunflowers at the strong leaf-pair stage, before elongated growth, clinging hulls or damaged leaves undermine their clean, nutty character.

Chilling belongs to the crop cycle.

Move harvested microgreens out of greenhouse warmth as soon as practical. Pack them loosely in clean food-safe containers and chill promptly. Do not store cut produce beside raw meat or unwashed vegetables. Microgreens offer their best quality when the route from clean cutting to the kitchen stays short.

08 / Diagnosis

Read a failed tray as a clue—not as a reason to water more automatically.

Negative image
Long, pale stems

Stretched and leaning

Even light is probably lacking, often together with a cover left on too long or excessive sowing density. Uncover at the appropriate time and move the crop into bright, filtered light. Also check whether plants are leaning towards the glazing. Extra warmth will not correct a weak, pale canopy and can intensify heat build-up.

Positive image
Dry and upright

Surface stays wet

Reduce the amount of water, irrigate gently through the lower tray and improve gentle air movement. Check the sowing pattern too: fine seed placed too densely creates a moist, felt-like surface even when the greenhouse is generally ventilated.

Negative image
Patchy emergence

Uneven germination

First check medium moisture and seed distribution. Dry edges, a waterlogged centre or clumped seed cannot produce an even stand. Moisten and level the medium beforehand. Also note whether the particular crop benefited from soaking, light pressing or a short controlled covering period.

Positive image
Cleanly cut, quickly chilled

Short storage life

Harvest only dry, sound leaves with cleaned tools. Limit time in greenhouse warmth, do not pack wet cut produce and chill promptly. If storage life remains short, review both the hygiene route and handling, pack moisture and temperature after cutting.

Questions from the workbench

Microgreen FAQ

Do microgreens need direct sun in a greenhouse?

No. Bright daylight is valuable, but intense direct sunshine behind glazing can quickly overheat shallow trays and stress delicate leaves. Choose a bright but temperable position with good ventilation and seasonal shading. Supplementary plant lighting is particularly useful when natural light is short or persistently unreliable during local winter conditions.

Must all microgreens be soaked and weighted?

No. Large seeds such as peas and sunflowers are often soaked, while fine brassica and radish seed usually do not need it. Covering and light weight also depend on crop, temperature and seed batch. Follow supplier guidance, check daily and respond to visible emergence rather than a blanket blackout timetable.

Can I grow several species in one tray?

It is possible, but single-variety trays are much more reliable when starting out. Species differ in seed size, water uptake, germination speed and ideal cutting time. Keep records for each crop first. Mixtures are easier and more precise to combine after harvest, without one crop needing cutting too early or too late.

Do microgreens need fertiliser?

Many microgreens complete their short cycle using seed reserves and a suitable growing medium. Extra nutrients should therefore not be added automatically. First establish even germination, sufficient light, careful bottom watering and a clean routine. Then follow crop-specific guidance from your seed or system supplier if the chosen method calls for supplementary nutrition.

Is a greenhouse suitable for young plants eaten raw?

Yes, provided growing is consistently treated as food production. This means drinking water, suitable seed, fresh medium, clean trays and tools, exclusion of animals, hygienic hands, airflow that allows drying and prompt chilling. Rainwater should not be used for this ready-to-eat crop without reliably verified water quality. A greenhouse alone does not make a batch safe; daily practice is decisive.

Sources and further reading

Develop your own growing notes with sound information.

These German and international specialist sources support the guidance on seed, hygiene, crop management and the distinction between sprouts and microgreens. They help assess risks, refine tray routines and document decisions about water, medium, climate and harvest in a traceable way.

BfR: Recognising and preventing STEC/EHEC food risks— German Federal Institute for Risk Assessment guidance on food-borne STEC/EHEC risks and prevention.
LAVES: Sprouts and seedlings— Lower Saxony State Office for Consumer Protection and Food Safety information on sprouts, seedlings and hygienic handling.
EFSA: Risk assessment of seed and sprouts— European Food Safety Authority scientific risk assessment for seed and sprout production.
Virginia Cooperative Extension: Greenhouse microgreen production— Technical guide to microgreen production in greenhouses and controlled indoor systems, including crop and system fundamentals.
Penn State Extension: Growing microgreens— Practical information on sowing, growing medium, light, watering, harvesting and common microgreen decisions.

Start with a clean, shadeable tray—and make the process repeatable.Classic aluminium greenhouse

Classic aluminium greenhouse Classic aluminium greenhouse