Sanitize seeds before planting to eliminate mold spores

Most mold problems originate from spores already present on the seed coat. Pre-treating seeds -- especially large seeds like sunflower, pea, and cilantro -- dramatically reduces mold outbreaks. Multiple methods exist ranging from free DIY to commercial products.

Hydrogen Peroxide Soak (DIY - Most Common)

• Use 3% food-grade hydrogen peroxide (available at pharmacies or health stores)
• Method 1 -- Direct soak: Submerge seeds in undiluted 3% H2O2 for 3-5 minutes, stirring once per minute for even coverage
• Method 2 -- Extended soak: Soak for 10-15 minutes in 3% solution for higher mold-spore reduction
• Do not exceed 15 minutes -- air pockets form between seed and seed coat, causing uneven germination
• Do not use concentrations above 3% for soaking -- damages seeds
• If using 35% food-grade H2O2, dilute to 3% first (1 part 35% to 10 parts water)
• Rinse seeds thoroughly with clean water after treatment
• Proceed to normal soaking or direct planting

Vinegar Soak

• Use standard 5% white distilled vinegar
• Soak seeds for 15 minutes (Kansas State University extension recommendation)
• Alternative: 1 teaspoon vinegar per cup of water as a milder soak
• Rinse thoroughly after treatment
• Less effective than hydrogen peroxide but readily available

OxiDate 2.0 Seed Treatment (Commercial)

• Dilute at 1:100 ratio (64 fl oz per 50 gallons of water)
• Submerge seeds according to label directions
• OMRI-listed, no residue

Grapefruit Seed Extract (GSE)

• Add 10 drops of GSE per cup of seed-soaking water
• Contains naringin and limonin which disrupt fungal cell membranes
• Evidence is mostly anecdotal; lab studies show antifungal properties but limited field validation
• Available at True Leaf Market as a microgreen-specific product

Which Seeds Need Treatment Most

• Always treat: Sunflower, pea, cilantro, wheatgrass -- these have tough outer shells that harbor spores and require pre-soaking anyway
• Recommended: Any large-seeded variety
• Usually unnecessary: Small brassica seeds (radish, broccoli, kale) that are not pre-soaked
• Never soak: Mucilaginous seeds (basil, chia, flax, arugula) -- they gel and clump; use spray treatment instead

Tips

• Combine seed treatment with clean trays and fresh medium for maximum prevention
• If mold recurs despite seed treatment, the problem is likely environmental (humidity, airflow) rather than seed-borne
• Buy seeds from reputable suppliers (True Leaf Market, Johnny's Selected Seeds, Bootstrap Farmer) who store seed properly
• Never mix vinegar and hydrogen peroxide together in one container -- this creates peracetic acid which is toxic and irritates skin, eyes, and lungs