Key Terms
Scarification: Mechanical or chemical disruption of the seed coat to accelerate water uptake and the onset of germination. Applied to seeds with a hard, impermeable coat.
Stratification: Cold, moist storage at low temperatures to break dormancy mechanisms. Required for seeds that need winter exposure before spring germination.
Seed disinfection: Chemical or physical treatment that reduces or eliminates pathogenic microorganisms on or inside the seed coat.
Disinfection: When and How
Disinfection is relevant for microgreen and sprout production where microbial risk is systemic, and for recurring problems with Pythium or Fusarium that point to contaminated seed sources.
Hot Water Treatment
- Temperature: 50–55°C for 5–10 minutes
- Eliminates most surface and some internal pathogens with minimal germination loss
- Warning: temperatures above 60°C or durations beyond 15 minutes damage the embryo
- Requires a precise thermometer and timer
Sodium Hypochlorite (Bleach)
- Concentration: 1–2% solution
- Duration: 1–2 minutes, followed by thorough rinsing
- Effective against most surface bacteria and some fungi
- Does not penetrate the seed coat; ineffective against internal contamination
Hydrogen Peroxide (H₂O₂)
- Concentration: 0.5–1% solution
- Duration: 5–10 minutes, followed by rinsing
- Milder than chlorine; suitable for systems where chlorine residues are undesirable (bioponics)
- Breaks down to water and oxygen with no residue
Scarification: Which Seeds Require It
Most vegetable crops and microgreens grown hydroponically do not require scarification. Exceptions include:
Legumes (pea, bean, soya, chickpea): Light scarification — rub between sheets of sandpaper or shake in fine sand for 30–60 seconds. Followed by soaking to accelerate and even out germination.
Beetroot and chard: Technically the "seed" is a cluster containing 2–4 true seeds in one fruit. Soaking for 4–6 hours before sowing gives better results than scarification.
Stratification: Rarely Needed Under Controlled Conditions
Stratification requires storage at 2–5°C in moist conditions for 2–8 weeks. Necessary for woody perennials and herbaceous perennials with natural winter dormancy: lavender, some herbs, fruit trees.
Most annual vegetables and herbaceous crops grown indoors do not require stratification.
Commercial Seed Coatings: Labels and What They Mean
Most commercial seed is supplied pre-treated — coated with fungicides or insecticides (pink, blue, or green colouring):
- Not suitable for sprout or microgreen production intended for food
- Does not meet organic certification requirements
- Residues may affect substrate microbiology
Three Mistakes That Cost the Most
Skipping disinfection for sprouts because "it always worked before." Surface Salmonella is invisible and odourless. Commercial sprout production requires mandatory seed disinfection.
Extending hot water treatment or raising the temperature "to be safe." Water above 55°C for more than 10–12 minutes, or treatment at 60°C, causes significant germination loss.
Scarifying seeds with a thin coat (radish, basil, rocket). Mechanical damage to the coat injures the embryo and reduces germination rate.
Confirming Treatment Was Done Correctly
For sprout production: a documented disinfection protocol specifying method, temperature or concentration, and duration. After treatment, germination rate should not drop more than 5–10% compared to an untreated control.