Question: Should I sanitize my microgreen seeds before beginning germination?

Answer: IMHO, Yes. Sanitizing is cheap insurance against big problems. It’s a well know fact that seed-borne viruses and pathogens can damage or destroy any crop.  While many growers report that they successfully grow without having santized their seed many more ask what they should do to prevent the mold and fungus that just wiped out an entire tray of their microgreens.  This common seeding problem is called ‘damping off’ or ‘seedling blight’. Sanitizing seed is just one more preventive measure in addition to making sure that the seed was purchased from a reputable source, that the grow trays are clean and sanitized, that the grow room has well-circulated air, that the microgreen seeds aren’t laid down too densely on the grow media, and that the seeds are not being over-watered or sitting in pooled water.

Question: What should I use to sanitize my microgreens?

Answer:  By far the safest and more commonly used sanitizer is Food-Grade Hydrogren Peroxide.  Some growers use off-the-shelf Hydrogen Peroxide from the local drugstore, but you should know that this product is not classified as “food-grade” because it has stabilizers added to it to minimize its decomposition under normal storage and handling conditions.  Which specific stabilizers are added to your locally available commercial hydrogen peroxide are usually not printed on the label.  According to USP Technologies¹, a a provider of municipal water treatment services, the most common stabilizers added to Hydrogen Peroxide include:

• Colloidal Stannate and Sodium Pyrophosphate (present at 25 – 250 mg/L)
• Organophosphonates (e.g., Monsanto’s Dequest products) are increasingly common
• Nitrate (for pH adjustment and corrosion inhibition) and Phosphoric Acid (for pH adjustment)
• Colloidal Silicate is used to sequester metals and thereby minimize H2O2 decomposition in certain applications that depend on the bleaching ability of H2O2 in alkali.

Plain and simple, these substances are not intended for human consumption.

If you’ve decided to use food-grade hydrogen peroxide then I might suggest you buy from Bluebonic Industries, a family-owned business which sells on Amazon. Their 32 oz. bottle of food-grade 12% Hydrogren Peroxide is competively but if you’re all high-volume user you’ll find that their 128 oz. bottle is a terrific bargain with free shipping.

Some growers use diulted Chlorine Bleach to sanitize both their trays and their seed.  Their choice is predicated upon bleach being the recommended sanitizing solution for surfaces and utensils in commercial food kitchens.  Assuming that all of the bleach residue is completely rinsed away this method is likely fine and comes down to personal preference, budget, and marketing choice. Personally, bleach sounds more potentially harmful and corrosive than “Food-Grade Hydrogren Peroxide” which naturally degrades into water on it’s own.  But the truth is that both Chlorine Bleach and Undiluted (12% or 35%) Hydrogen Peroxide can be potentially dangerous if not handled correctly.  In Chemistry 101 you learn that a Base can burn as much as an Acid, so rubber gloves should be used when handling these solutions.

To sanitize your seed trays, begin by scrubbing and rinsing off any grow material residue and organic matter, then mix 1 part bleach to 9 parts water and soak the trays for 15-20 min. before rinsing well, then let them air dry.²

US EPA has approved 2% chlorine from Calcium Hypochlorite as a seed sanitation method before sprouting. Tests have shown no residual chlorine on finished sprouts. (Dr. Rob Wick, Sprouters Journal of the ISGA, Spring 1999). Calcium Hypochlorite granules contain 40-78% AC (available Chlorine) and are used to disinfect swimming pools. Household Bleach contains Sodium Hypochlorite which contains 10-12% AC which is why it is not as good a disinfectant for swimming pools as Calcium Hypochlorite. 

The recommend method is to add 3 oz calcium hypochlorite to 1 gal of warm water. SAFETY NOTE: Never add water to calcium hypochlorite, be sure to add the calcium hypochlorite to the water. There is a difference. Pour the solution over the seed, mix thoroughly, and let stand 10-20 minutes. Drain and rinse the seed thoroughly in potable water.³

Credit to Curtis Stone for sharing his formula for:

‘The Poor Man’s Sanitizer for Microgreens’

Ingredients:

1. One quart of Distilled or Purified Water
2. 4 tsp White Vinegar
3. 4 tsp Food-Grade Hydrogen Peroxide (H2O2)

Equipment:

• Measuring Spoons
• Stainless Steel Mesh Strainer(s)
  or a
• Spaghetti Colander
• Clear Measuring Pitcher

Directions:

Mix 4 teaspoons of white vinegar and 4 teaspoons of 3% food-grade hydrogen peroxide with 1 quart of distilled or purified room-temperature water.

Pour the solution into a container completely submersing your seeds and and soak the seeds for 5-10 minutes.

Strain seeds out from the solution using either a spaghetti colander or stainless steel mesh strainer depending on the size of your seed.

Rinse seeds and being the germination process.

Furthermore:

Some growers have reported that they take an extra precautionary steps of applying their microgreens sanitizing solution to their grow media, whether it’s Biostrate or Coconut Coir. Like sanitized seed, the treated grow media should be rinsed with clean water before the seeds are laid down.

You’re welcome to download and print our free Microgreens Sanitation Check List to add to your Microgreens Grow Binder.

FootNotes:

1. USP Technologies : ‘What re H2O2 stabilizers and will they affect my application?’  Last Updated: 08/01/2011
2. Louisiana State University ‘Good Agricultural Practices’ Project: ‘Vegetable Seed Sanitation: Best Practices to Ensure On-farm Food Safety‘ Sept. 2015
3. International Specialty Supply: ‘Seed Sanitation‘