Microgreens are fast-growing, but that also means problems can develop quickly. A tray can go from looking healthy to wilted, mouldy or uneven within a day or two.
The most useful way to troubleshoot microgreens is to start with the symptom. Poor germination, mould, yellow seedlings and wilting can have completely different causes, and adding more water or airflow without identifying the problem can sometimes make it worse.
Microgreen Troubleshooting: Quick Diagnosis
| Problem | Likely Causes | Check First |
|---|---|---|
| Seeds not germinating | Temperature, moisture, old/low-vigour seed, incorrect soaking or seed requirements | Temperature and moisture |
| Patchy germination | Uneven sowing, moisture or tray contact | Seed distribution and moisture across the tray |
| Seeds rotting | Excess water, poor drainage, unsuitable temperature or disease | Smell, seed texture and saturation |
| White fuzz | Root hairs or mould | Where and how the white growth appears |
| Seedlings collapsing | Damping-off, severe water stress or damaged stems | Stem at growing-medium level |
| Yellow microgreens | Recently uncovered, insufficient light, root problems or other stress | How long they have been under adequate light |
| Long, weak or leggy growth | Insufficient light | Light intensity and distance |
| Wilting | Too little water, excessive heat or root problems | Growing-medium moisture |
| Uneven tray | Uneven seed density, water, light, temperature or tray level | Look for a pattern across the tray |
| Seed hulls stuck to leaves | Normal crop characteristic, insufficient moisture during germination or emergence conditions | Crop type and germination method |
| Bad or sour smell | Rotting seed, excessive moisture or microbial growth | Seed and root zone |
| Algae | Persistent surface moisture combined with light | Growing-medium surface |
| Crop growing too slowly | Temperature, light, crop type or poor seedling establishment | Compare conditions with the requirements of that crop |
1. My Microgreen Seeds Aren’t Germinating
Don’t immediately assume that seed which has not emerged is dead.
Germination is strongly affected by temperature and moisture, and different species germinate at different rates. Basil, coriander and some herbs, for example, should not be judged according to the same timetable as fast-germinating brassicas or radish.
Check:
- Is the growing medium moist without being saturated?
- Has the surface dried during germination?
- Is the temperature suitable for the species?
- Was the seed sown too deeply?
- Does the crop normally benefit from soaking?
- Was soaked seed left in water for too long?
- Has enough time actually passed for this variety?
- Is the seed old or has it been stored poorly?
2. Why Is Germination Patchy?
If one part of the tray germinates strongly while another part is sparse, look for a pattern.
Patchiness can result from uneven seed distribution, uneven moisture, an unlevel tray, differences in growing-medium depth or poor seed-to-medium contact.
The edges of a tray can also behave differently from the centre because they may dry more quickly.
If you consistently see the same pattern on trays in the same position, investigate the growing environment. Light, airflow or heat may be uneven across the shelf.
For crop-specific starting rates, see our Microgreen Seeding Density Chart.
3. Why Are My Microgreen Seeds Rotting?
Rotting seed is different from seed that is simply slow to germinate.
Affected seed may become soft, slimy, discoloured or develop an unpleasant smell.
Common contributing factors include:
- excessive moisture
- poor drainage
- water pooling in the tray
- very dense sowing
- unsuitable temperatures
- damaged or deteriorated seed
- contaminated equipment or growing medium
Large seeds that are soaked before sowing can be particularly noticeable when something goes wrong because there is a large amount of moist organic material packed into the tray.
Don’t leave soaked seed sitting in stagnant water indefinitely. Drain it according to the requirements of the crop before sowing.
4. Is the White Fuzz Mould or Root Hairs?
This is one of the most common sources of confusion when growing microgreens.
Many healthy seedlings develop fine white root hairs. These are particularly obvious on crops such as radish and can look surprisingly similar to fungal growth.
Root Hairs
- Concentrated around individual roots
- Usually fine and relatively uniform
- Appear as part of normal root development
- Often become much less visible when wet
- Usually appear consistently across healthy seedlings
Possible Mould
- May spread between seeds or across growing medium
- Can form irregular patches
- May occur around dead or decomposing material
- May be associated with rot or unpleasant odour
- Does not simply behave like normal root hairs when watered
5. Why Is Mould Growing on My Microgreens?
Mould is not caused by one single growing mistake.
Dense sowing, excess moisture, warm conditions, high humidity, poor airflow, decaying seed and contaminated growing equipment can all contribute.
Warm, humid conditions are particularly favourable to damping-off and other disease problems in densely grown seedlings.
If mould repeatedly develops, check the whole system:
- Are you sowing too densely?
- Are trays remaining saturated?
- Is water draining properly?
- Is the crop covered for longer than necessary?
- Is there air circulation once the crop is uncovered?
- Are trays properly cleaned between crops?
- Is old plant material remaining in the growing area?
- Does the problem become worse during warm, humid weather?
Our guide to growing microgreens in hot, cold and humid Australian conditions explains how temperature, humidity, airflow and moisture interact.
6. What Is Damping-Off?
Damping-off is a disease problem affecting germinating seed and young seedlings.
Several pathogens can cause damping-off, including species of Pythium, Rhizoctonia, Fusarium and Phytophthora.
There are two broad forms:
- Pre-emergence damping-off: seed or very young seedlings rot before successfully emerging.
- Post-emergence damping-off: seedlings emerge but the stem or root tissue deteriorates and the seedling collapses.
Look closely at collapsed seedlings. Damping-off often produces soft, discoloured or narrowed tissue around the stem near the growing-medium surface rather than an otherwise healthy seedling simply leaning over.
Excessive moisture, overcrowding and unsuitable growing conditions can increase disease pressure.
7. What Should I Do With a Tray Affected by Damping-Off?
Once seedlings are badly affected by damping-off, they generally do not recover into a healthy microgreen crop.
For a home grower, attempting to rescue a heavily diseased tray is usually not worthwhile.
Discard affected plant material and growing medium, then thoroughly clean the tray before starting another crop.
For the next sowing:
- use clean trays
- use fresh, suitable growing medium
- avoid excessive watering
- check drainage
- avoid excessive seeding density
- manage temperature and airflow
8. Why Are My Microgreens Falling Over?
Not every fallen seedling has damping-off.
First check whether the plants are actually damaged.
A tray may wilt or collapse temporarily because the growing medium has become too dry. If healthy seedlings recover rapidly after appropriate watering, water stress was probably involved.
Seedlings can also become structurally weak when they are excessively elongated.
If stems are soft, narrowed, discoloured or rotting at growing-medium level, disease becomes a much greater concern.
9. Why Are My Microgreens Yellow?
Yellow microgreens are not automatically unhealthy.
Seedlings that have germinated in darkness are naturally pale because chlorophyll development has been limited. Once moved into adequate light, many crops begin greening relatively quickly.
If seedlings remain pale after adequate light exposure, investigate further.
Possible causes include:
- insufficient light
- excessive or persistent root-zone moisture
- root damage
- temperature stress
- nutritional problems in longer-growing crops or certain soilless systems
Start with light and root-zone conditions rather than immediately adding fertiliser.
See our Microgreen Lighting Guide for more information.
10. Why Are My Microgreens Leggy?
Long stems aren’t always a problem. Microgreens are often deliberately encouraged to elongate during germination or blackout because a longer stem can make harvesting easier.
But after the crop is under lights, continued weak, stretched growth usually points towards inadequate light.
Signs can include:
- very long, thin stems
- seedlings leaning towards a window or light source
- weak growth
- large differences between the side nearest the light and the opposite side
Move the crop into appropriate light and check whether the light source is sufficiently intense and evenly distributed.
11. Why Are My Microgreens Wilting?
The first thing to check is the growing medium.
If it is dry and the crop recovers quickly after watering, the tray probably simply became too dry.
Hot conditions, direct sunlight and excessive airflow can substantially increase water demand.
If the medium is already very wet, however, do not assume wilting means the crop needs more water. Saturated root conditions, disease or damaged roots can also produce unhealthy, wilted plants.
See How to Water Microgreens for our complete watering guide.
12. Why Is One Side of My Tray Growing Better?
An uneven tray often gives you a useful clue because the pattern can reveal the cause.
Check whether:
- seed was distributed evenly
- the tray is level
- water accumulates at one end
- one edge dries faster
- one side is closer to a window or grow light
- a fan blows predominantly across one section
- the growing medium is deeper on one side
Rotating trays can compensate for some environmental variation, but it is better to correct a consistently uneven growing setup where possible.
13. Why Are Seed Hulls Stuck to My Microgreens?
Seed hulls are a normal nuisance with some microgreen varieties.
As seedlings emerge, the cotyledons normally separate from the seed coat. Sometimes the hull remains attached.
This is particularly noticeable in crops with substantial hulls, including sunflower.
A suitable germination method, adequate moisture and appropriate contact or weighting for crops that benefit from it can help seedlings shed their hulls as they emerge.
Once the crop is growing, don’t aggressively pull hulls from delicate seedlings. Many loosen naturally as the leaves expand.
See our Microgreen Weighting & Blackout Guide.
14. Why Do My Microgreens Smell Bad?
Healthy microgreens and moist growing medium have a characteristic fresh, earthy or crop-specific smell.
A strong sour, rotten or unpleasant smell deserves investigation.
Check for:
- soft or decomposing seed
- slimy material
- standing water
- dead roots
- fungal growth
- poor drainage
- stagnant conditions
15. Why Is Algae Growing on My Microgreen Tray?
Green algae on the growing-medium surface usually indicates that the surface is receiving light while remaining persistently moist.
A small amount doesn’t necessarily destroy the crop, but repeated algae is a useful sign that the surface environment is staying wet.
Check watering frequency, drainage, growing-medium structure and whether water is continually sitting on the surface.
Once seedlings are established, bottom watering can help reduce unnecessary wetting of the surface and foliage.
16. Why Are Mushrooms Growing in My Microgreen Tray?
Occasionally mushrooms or other visible fungi can appear in organic growing media.
Fungi naturally occur in organic material, so their presence doesn’t necessarily mean that the microgreens themselves have a plant disease.
However, visible fungal fruiting bodies indicate biological activity in the growing medium and should prompt you to check the medium, moisture and hygiene of the growing system.
For edible microgreen production, starting each crop with a clean, appropriate growing medium is preferable to repeatedly reusing an old root-filled medium.
17. Why Are My Pea Microgreens Rotting?
Peas present a particular challenge because a microgreen tray contains a large quantity of seed.
The seeds are usually soaked before sowing, and a densely planted tray can retain considerable moisture.
If peas repeatedly rot:
- check the soaking time
- drain soaked seed properly
- don’t sow at an excessive density
- avoid saturated growing medium
- check the tray drains freely
- avoid leaving the crop covered unnecessarily
- check temperature and airflow
Some individual seeds may fail while the remainder of the tray grows normally. Widespread soft, decomposing seed is a different problem and needs investigation.
18. Why Is Sunflower Difficult to Grow?
Sunflower microgreens can produce an excellent crop, but their large seeds and hulls make them different from fine-seeded brassicas.
Common sunflower problems include:
- hulls remaining attached
- uneven germination
- individual seeds rotting
- mould developing around failed seed
- poor root establishment
- overcrowded trays
Correct seeding density is particularly important. More seed does not necessarily produce more usable sunflower microgreens.
For a standard Seedmart 30 × 35 cm tray, our current practical starting range for black sunflower is approximately 120–140 g of dry seed. Adjust according to seed size, germination and your growing system.
19. Why Are My Microgreens Taking Too Long to Grow?
First check whether the crop is actually late.
Microgreens have very different growth rates. A harvest time that is normal for coriander would be extremely slow for radish.
If a normally fast crop is substantially behind schedule, investigate:
- low temperature
- inadequate light after germination
- poor germination
- root-zone problems
- poor seed vigour
- crop-specific growing requirements
Commercial growers should record sowing and harvest dates rather than relying on memory. Seasonal changes become much easier to identify when you can compare successive crops.
20. Germination Percentage Isn’t the Whole Story: Seed Vigour
A laboratory germination percentage tells you how many seeds germinated under the conditions of that test. It doesn’t describe every aspect of how a seed lot will perform under different growing conditions.
Seed vigour describes characteristics affecting the activity and performance of seed during germination and seedling emergence.
This helps explain why two seed lots with similar germination percentages can sometimes establish differently when subjected to environmental stress.
Seed performance can be affected by factors including genetics, seed production, maturity, processing, storage and age.
21. How to Clean Microgreen Trays Between Crops
Good tray hygiene reduces the amount of old roots, organic matter and contamination carried from one crop into the next.
Remove roots, growing medium, seed hulls and other plant material, including material trapped in drainage holes.
Wash the tray thoroughly with detergent and water to remove soil and organic residues.
For commercial food production, use an appropriate food-contact sanitiser according to its label and your food-safety procedures.
Allow clean trays to dry and keep them away from dirty growing media, used trays and contaminated surfaces.
Cleaning and sanitising are different processes. Sanitiser works most effectively after soil and organic residues have first been physically removed.
22. Don’t Try to Fix Every Problem With More Water
This is one of the most useful troubleshooting rules for microgreens.
Wilting can indicate insufficient water, but poor germination, yellowing, collapsed seedlings and slow growth can have many other causes.
Adding water to a tray that is already wet can increase disease pressure and reduce oxygen around the roots.
Before watering, physically check the growing medium and the weight of the tray.
23. Don’t Try to Fix Every Mould Problem With More Airflow
Air circulation is important, particularly around dense microgreen canopies.
But a fan cannot compensate for continuously saturated growing medium, standing water, excessive seed density or decomposing seed.
Use airflow as one part of the growing system rather than as a treatment for every fungal problem.
When Should You Discard a Microgreen Tray?
Microgreens are eaten very young and often raw or only lightly cooked, so be conservative with obviously deteriorating crops.
Discarding a tray is appropriate when there is widespread rot, obvious disease, extensive unexplained fungal growth, strong decomposition or a crop that you do not consider suitable for consumption.
Don’t taste a questionable tray to determine whether it is safe.
Preventing Problems Before They Start
Good troubleshooting is useful, but prevention is easier.
Start with seed appropriate for the intended microgreen crop and store it correctly.
Overcrowding makes water, airflow and disease management more difficult.
Keep germinating seed moist without leaving established trays continuously saturated.
Remove crop debris and clean trays properly between growing cycles.
Once the crop enters the light stage, sufficient light prevents unnecessary weak, stretched growth.
Temperature and humidity change water demand and disease pressure throughout the year.
Microgreen Problem-Solving Checklist
When a crop goes wrong, work through these questions before changing several things at once:
- Seed: Did it germinate normally in a separate test?
- Crop: What is normal for this particular species?
- Temperature: Was the tray unusually hot or cold?
- Water: Is the growing medium actually dry, moist or saturated?
- Density: Was too much seed used?
- Drainage: Can excess water leave the root zone?
- Light: Is the crop receiving adequate light after germination?
- Airflow: Is humid air trapped around the crop?
- Hygiene: Were the tray and equipment clean?
- Pattern: Is the problem random, crop-wide or concentrated in one part of the tray?
Related Microgreen Growing Guides
Grow Microgreens With Seedmart Australia
Seedmart supplies microgreen seed for home growers and commercial production, with pack sizes ranging from small growing trials through to bulk quantities.