Neonatal Gardening: Sterilizing Your Seed Trays for Propagation

Photo by Markus Spiske on Unsplash

May I a small house and large garden have;
And a few friends, And many books, both true. ~ Abraham Cowley

If you’re a gardener, planting seeds every spring and summer is a rite of passage that heralds the rebirth of hope, planned for fruits, herbs, vegetables, and flowers, and the anticipation of the new season’s harvest.

Rather than take a chance on the questionable care and lineage of big box store plants, savvy gardeners know that propagating seeds purchased from the best quality seed companies is the wisest, most economically sound way to get wonderful harvests or display gardens.

To help budding gardeners take the plunge, read my handy guide on the first most important step in beginning to propagate seeds.

How to Disinfect Seed Trays

If you want to have vigorous, healthy, plants you have to prepare properly by treating seedling germination and propagation with care. Think of the trays and equipment used to propagate your seeds as a neonatal seedling unit.

These seedlings need plenty of love and attention, need to be kept warm, must be raised in a safe environment, and need to be protected from potentially harmful germs, plant diseases, and damping off.

To avoid making your seedlings sick, you must always clean and disinfect your seed propagation equipment, propagation trays, and ensure your seeding medium is sterile before you start your seeds; and you need to do this every time you propagate seeds.

The sterilization process includes disinfecting gloves, seed trays from the previous growing season and new ones you just purchased, and anything, including dirt, that will come in contact with your seeds. You never know what germs, pathogens, pests, or fungi you may be exposing your seeds to so like the old saying goes, “An ounce of prevention is worth a pound of cure.”

Sterilizing with Hydrogen Peroxide

Now that you know you need to sterilize the seed trays you also need to know who to sterilize them so before you reach for the nearest bottle of bleach for this process, there are some essential things to consider, chief among them the toxicity of chlorine bleach. It can be deadly if ingested or dangerous if it comes in contact with your skin or other body parts, and it can ruin fabric, etc.if it splashes on your clothes and other surfaces.

It’s also terrible for the environment, which is why many Master Gardener™ Programs recommend never using bleach and instead recommend hydrogen peroxide (aka H2O2).

So Why Choose Hydrogen Peroxide?

Hydrogen peroxide or its chemical name H2O2 contains two atoms of hydrogen and two atoms of oxygen and occurs naturally in the environment. It’s similar to water (aka H2O), which includes two atoms of hydrogen and one atom of oxygen, and this similarity is what makes hydrogen peroxide safer to use in the garden than toxic chlorine-based chemicals.

• Those two atoms of oxygen in hydrogen peroxide are useful in the garden because oxygen helps plants fight off and kill diseases, pests, and unwanted organisms (fungi, algae, bacteria, nematodes) and makes peroxide a safer alternative to synthetic chemical fertilizers, pesticides, and fungicides.
• Hydrogen peroxide kills bacteria and viruses by destroying their cell walls and breaking those cells down into oxygen and water without leaving any toxic chemical residues on plants or in the environment.
• The CDC considers commercially produced 3% non-food-grade hydrogen peroxide a stable and effective disinfectant and sterilizer when used on garden tools, equipment, etc.

Hydrogen Peroxide and Safety Precautions

I recommend sterilizing your seedling trays with ordinary hydrogen peroxide at a strength of 3%. This is the kind sold at your local grocery store, hardware store, or online, and it can be bought in manageable sizes for just this sort of project.

However, that doesn’t mean you don’t have to use caution when sterilizing with hydrogen peroxide. Generally, 3% hydrogen peroxide is shelf-stable when properly stored, but there are some safety precautions you need to know.

1. It has combustible, corrosive properties and should always be handled with care.
2. It should never be stored near a heat source or combustible equipment.
3. It should be stored out of the reach of children and pets.
4. It should never be stored near any flammable liquids or equipment.
5. The container should be safe for storage of this type of corrosive combustible.
6. It degrades quickly when exposed to light and sunlight and thus should be stored in a dark container that doesn’t let in any light.
7. Wear rubber gloves and goggles and long sleeves to protect your skin and eyes because peroxide can damage and burn sensitive tissues.
8. If you have cuts, burns, or open wounds wear rubber gloves because medical studies continue to show that hydrogen peroxide is not only ineffective when it comes to wound healing, it’s also believed that because hydrogen peroxide works by killing bacteria, it kills both “good” healing bacteria and “bad” infection-causing bacteria and delays the healing process.

Sterilization Procedure

Step One:

Clean tools, trays, plant labels, etc. of dirt, debris, etc. before disinfecting.

Step Two:

Scrub the trays and containers with warm, soapy water. Trying using a small amount of a natural cleaning concentrate like On Guard Cleaning Concentrate. You can easily cover all of the surfaces by spraying On Guard onto the trays, etc. This concentrate, by itself, will likely eliminate most of the issues that cause damping off but when combined with hydrogen peroxide is a safe sterilization mixture that ensures your new seeds have a safe, sterile growing environment.

Step Three:

Pour your peroxide into a large spray bottle and head with your trays and other equipment to a safe area away from the wind, rain, children, pets, or fabric. I use outdoor flat tubs, or large flat plastic containers are perfect for this, but you may also use your bathtub. First, place the trays, etc. into the bottom of the tub and then spray every part of every surface with a generous spray of hydrogen peroxide, let everything sit for an hour, and then rinse with clean water.

Step Four:

Wipe with clean, sterilized, dry cloths, and you’re ready to plant! This task is essential for eliminating germs and preventing damping off, and it’s time well spent.

Seed Tray Disinfecting Notes:

If you can, do this project outside and use a big plastic tub. Once rinsed either dry everything with a sterile towel or leave the trays to dry in the sun try because sunlight is a natural disinfectant. If you live in an apartment and have a balcony dry everything in the sun on your balcony otherwise, just follow the other instructions.

Why You Need to Prevent Damping Off

By the time you’ve sterilized your trays, soil, tools, etc. planted your seeds, waited for weeks for them to germinate and push their tiny heads up through the soil the last thing you want is to anxiously go to your trays and see black, shriveled, or dead little plants.

You may struggle to understand where you went wrong, and if you neglected to sterilize beforehand chances are your seedlings have died because of damping off. This seedling disease is most often caused by fungus or mold. Sometimes it affects just a few seeds, other times you can lose a whole tray to this nasty fungus.

Here are a few things you can do to prevent this catastrophe:

• Clean and disinfect pots, flats, and trays before you use them to start seeds, sorry, had to repeat this just to make sure it’s not ignored.
• Don’t reuse old, unsterilized soil.
• Keep your seedlings warm while they are sprouting.
• Water seeds or seedlings with lukewarm water, not ice cold.
• Don’t let the soil get too wet or too dry.
• Don’t crowd seedlings, it encourages moisture retention.
• Provide seedlings with sufficient light (usually 12–16 hours of consistent sunlight not diffused light from a window. Some people use fluorescent lights for seed starting seeds, but then you have to have a place for that equipment, and it also can cost a lot of money.

If your next step while you wait for your seedlings to grow and mature is building raised beds, standing beds, or vertical gardens, be sure to read my article Five Fantastic Ideas for Raised Garden Beds

I hope you enjoy the fruits of your labor. Happy Gardening!