"Saw white fluffy growth between the stems — reached straight for the fungicide. But in 80% of cases, mould on microgreens is not an external infection — it is a consequence of growing conditions: excess moisture, no air movement, sowing density too high."
Fungicides on a food product with a 7–10 day cycle is not an acceptable solution. The problem must be resolved through growing conditions, not by fighting symptoms.
Quick Glossary
- Mould on microgreens — visible fungal or mycelial growth on the substrate surface or stems. In most cases this is saprotrophic mould feeding on dead organic matter, not a parasitic infection, and it arises from incorrect conditions rather than contamination
- Damping-off — stem rot at the root collar zone. The stem thins, constricts, and the plant collapses. Causative agents: Pythium, Rhizoctonia, Fusarium under conditions of excess moisture and poor aeration
- Bacterial disease — bacterial infection of plant tissue. On microgreens it presents as wet, slimy spots on leaves or stems, often with an unpleasant odour
Mould on the Substrate: Not Always a Pathogen
It is essential to distinguish mould on the substrate surface between stems from mould on the plants themselves — these are fundamentally different situations.
Mould on the substrate (especially jute or coco) is in most cases saprotrophic, decomposing substrate organic matter under conditions of elevated humidity and poor ventilation. It poses no direct threat to the plant, but is a symptom of conditions under which a real problem will soon appear.
Mould or mycelium directly on stems and leaves already represents a pathogenic infection: Botrytis, Alternaria, or others. With such symptoms the tray is discarded — a fungicide on a product that will be eaten in 3–5 days is unacceptable.
Seed root hairs viewed from below resemble mould — long white threads, evenly distributed. The distinction is simple: root hairs are structured and emerge from each seed uniformly; true mould grows chaotically in patches, especially in wet and poorly ventilated areas.
Damping-Off: Conditions Matter More Than the Pathogen
Damping-off is the death of seedlings through stem rot at the root collar zone. The causative agents vary (Pythium, Rhizoctonia, Fusarium), but the condition is always the same: excess moisture combined with poor aeration in the root zone.
Symptom: the stem becomes thin and translucent in its lower section; the plant collapses even when the leaf is still alive. It typically begins as a cluster — a few adjacent plants — and spreads across the tray if conditions are not changed.
Cause: almost always in irrigation — substrate too wet under the cover, water left standing under the tray continuously, top watering after germination. Changing conditions — allowing the upper substrate layer to dry between waterings, improving ventilation — stops damping-off even without treatment.
With widespread damping-off in a specific batch of substrate or seed, the source must be checked: some coco mat or seed batches have elevated microbiological contamination. Sanitiser rinse between cycles and checking new materials are part of prevention.
Bacterial Disease: Odour and Wet Spots as Diagnosis
Bacterial infection on microgreens looks different from fungal: not a powdery coating, but wet, semi-transparent or slimy spots on leaves and stems, often with a sour or putrid odour. It spreads rapidly at high humidity and temperature.
Main sources: contaminated trays between cycles, water with high microbiological load, seed with surface contamination. Bacteria are present in any environment — the problem starts when conditions allow them to multiply to a critical concentration.
Prevention involves three steps: sanitation of trays and surfaces between cycles (chlorine, hydrogen peroxide, or quaternary ammonium compounds), water quality control, and air movement in the growing zone that prevents water droplets from sitting on leaves.
When bacterial disease is detected, the tray is discarded. Adjacent trays require inspection, and ventilation is increased. Post-incident protocol: a HACCP record — when, where, what action was taken, and the source of seed and substrate.
Three Mistakes That Cost the Most
Applying fungicides or bactericides to microgreens. A 7–14 day cycle leaves no time for residue clearance. The solution is agronomic only: conditions and sanitation.
Leaving the tray to "observe" at the first signs of damping-off. Damping-off progresses from three plants to a third of the tray within 24 hours if conditions have not changed. At the first symptoms, correct humidity and ventilation immediately.
Not washing trays between cycles. Organic residue and root systems from the previous cycle are the substrate and inoculation source for the next. Tray sanitation is a mandatory step between cycles.
Signs That Conditions Are Under Control
- Under the cover during germination, no condensate drips back onto the seeds
- After removing the cover, the upper substrate layer dries between waterings
- Air in the growing zone is moving; no stagnant pockets
- Trays are sanitised between cycles and fully dry before reuse