Germinating plant seeds, whether indoors or outdoors, can be hit or miss. Some species have a baked-in low percentage of seeds that germinate and some have a high percentage. For instance, you may have been disappointed that only half of your Swiss chard seeds germinated while there’s no stopping the cherry tomato seeds. Some lack of germination is due to the thickness of the seed coat, but it can also be the result of the age of the seed, how it was stored, and how much water or oxygen it received after planting.

You might have read that nicking or sanding seeds with hard coats like spinach, peas and beans helps the germination rate – this is called mechanical scarification. In this article, we’ll discuss chemical scarification in which you soak, rinse or mist seeds in a solution of water and hydrogen peroxide to increase their germination rate. Hydrogen peroxide has the added benefit of reducing bacteria, viruses and fungi that may have infected the seed.

Why soak seeds in water and hydrogen peroxide?

To germinate, seeds require:

• Vigor
• Light
• Water
• Temperature
• Oxygen

Vigor is simple – buy fresh seed.

Light is also simple: outdoor sunlight or indoor grow lights.

Watering is obvious but mistakes are easily made -indoors, never saturate the seeds or let them dry out. Outdoors, keep the soil damp but not soaked.

Temperature can be provided by heat mats when starting seeds indoors or warm soil temperatures outdoors.

But what’s harder to control is the seed’s need for oxygen. This is where chemical scarification can help by softening the seed coat and allowing oxygen (and water) to reach the dormant seed inside. The ability of the seed to access oxygen means the difference between germination or not.

Studies show that seeds soaked in solutions of various percentages of hydrogen peroxide and water improve germination rates by helping to break down the seed coating. This allows the seed to receive oxygen. Hydrogen Peroxide’s chemical structure (H2O2) is close to that of water (H2O), but contains an extra molecule of oxygen.

Seeds that have hard, thick seed coats that physically prevent water or oxygen movement into seeds are said to have physical dormancy. In order to start the germination process of physically dormant seed, the exterior seed coat must be penetrable by water. Temperature, scarification, or alternating freezing and thawing cycles can create conditions favorable to the germination of a dormant seed.

When dormancy is broken, the embryo inside the seed receives a signal to begin the germination process, enabling gardeners to have a head start or to germinate difficult seeds.

Dormant seeds can… be treated with hydrogen peroxide (H2 O2 ). The seeds are soaked in a 1-3% solution for 5 minutes to 48 hours, based on the hardness of the seed coating.

The Sleeping Seed: An Overview of Dormancy and Treatments for Optimal Seed Germination, University of the District Of Columbia (pdf download)

How gardeners can use H2O2 to help seeds germinate

There are a few ways you can use a solution of hydrogen peroxide to help germination. Please follow the recommendation here and don’t overdo it – too much hydrogen peroxide in the solution may damage the seeds.

The safest seed soak is to use 1 ounce of 3% food grade hydrogen peroxide in 1 pint of water and let the seeds soak for 2-24 hours, depending on the thickness of the seed coat. Food grade H2O2 doesn’t have the stabilizers and heavy metals found in the brown bottle varieties and is safe to use around food. Hydrogen peroxide can also reduce viruses, bacteria and fungi that may be lingering on your seeds. Some claim it’s a good way to prevent “damping off”, a common problem for gardeners who start seeds indoors.

As the seed soaks, you should see noticeable swelling. This is a good thing – it’s taking on water. When the seed is swollen, remove it from the soak and wash it in fresh water. Plant immediately.

You can also arrange to plant seeds on paper towels and dampen (not soak) the towels with the H2O2 + water solution. Then fold the towels to cover the seeds so that each seed is in total contact with the damp towels. Keep the towels at room temperature and mist the towels lightly each day to keep them damp. Soon, sprouts will emerge (germination). They should be planted immediately in pots or in your garden. This is also a fun activity to introduce kids to gardening and plant science.

Will too much hydrogen peroxide harm seeds?

Yes. Studies show that high concentrations of H2O2 actually harms the seed after it penetrates the seed coat. Go easy and use the formula above for 3% hydrogen peroxide diluted with water.

Sources: The Sleeping Seed: An Overview of Dormancy and Treatments for Optimal Seed Germination, University of the District Of Columbia; Increased Oxygen Bioavailability Improved Vigor and Germination of Aged Vegetable Seeds, American Society for Horticultiral Science; What is a seed?, New York Botanical Garden.