Quick and Dirty Guide to Seed Stratification

What is Stratification?

Stratification is the process that happens to the seed to break dormancy. This can be done thought natural means in the environment or it can be done manually by humans. Stratification occurs naturally to seeds. Natural stratification methods include laying in cold soil throughout winter. It can be done by passing through the digestive track of a bird or a bear. It can also be artificially done.

Why Stratify?

Certain seeds need specific forms of stratification for them to germinate. If the right conditions or not met then the plant may never germinate. To increase the chances of your seeds germinating you must allow the seed to either naturally stratify or simulate stratification yourself.

What Are Methods of Stratification?

There are different ways of stratifying seeds. Each seed has different requirements and combinations of stratification methods. I will describe a few general strategies to chemically stratify and physically stratify.

Physical Stratification

Using Temperature to Stratify

• Cold Temperatures

This is one of the most common stratification needs for seeds. Most seeds in the Pacific Northwest have adapted to need a cold wet winter for seeds to germinate. This cold and wet conditions help to break down the seed coat allowing the seedlings to sprout in the spring. You can either take advantage of the natural winter and sow seeds outside in fall or you can mimic these conditions by placing the seeds in the fridge. You can place seed packets in the fridge if the plants only require cold for stratification or you can mix the seeds with sand or between moist paper towels and place these trays in the fridge. If you are starting a large number of seeds, this can take a lot of space in the fridge.

• Hot Temperatures

Some seeds require hot temperatures to break dormancy. For these seeds you can place the seeds in water that is just about to boil. You will then allow the seeds to remain in the water until the water cools. Other seeds can be kept in the freezer and then place in the near boiling water.

• Scarification

Scarification is a technique that physically removes some of the seed coat in order to allow moisture to enter the seed leading to germination. This can be done in a number of way. For seeds you can simply take a nail file or sandpaper block and gently scratch the outside of the seed. For some seeds you can take the tip of a knife and nick the outer coating.

Chemical Stratification

You can also stratify seeds with chemicals. This should be done carefully as many of the chemicals used in this process can be dangerous to people. Insure you use all the appropriate personal protective gear such as goggles and gloves.

IMPORTANT: If you do not have experience working with acids or do not feel comfortable Please stick to using the methods described previously.

Many seeds come from the fruits of plants. Many of these fruits are eaten by birds and other wildlife. Naturally the fruit and seed will pass through the digestive tracts of these animals resulting in a chemical scarification from the stomach acids of the animals. You can mimic this process by soaking seeds in acid.

To use this method you will want to place the seeds into glass lab ware. You will then pour concentrated sulfuric acid over the seeds. Stir the seeds in the acid for the set amount of time needed for that specific species. Some species need longer than others due to the thickness of the seed coat. When the appropriate time has passed, rinse the seeds with clean water through a screen for 10 or more minutes to ensure all the acid has been rinsed from the seeds.

Hopefully some of these methods of stratification can help you increase your rates of germination. Remember to research the needs for each species. Check out past posts of Harvesting and Storing Seeds. Happy Seed Starting!