Some seeds have a harder outer coat than others. This outer coat is meant to protect the seed from the natural harsh conditions it may experience during dormancy until the time is right for germination. When producing plants in a greenhouse it is common to utilize plant hormones to break this dormancy. But naturally, the stratification requirements for these hard seeds to germinate in controlled settings like your garden are similar to the conditions they would face in the wild. To mimic these experiences there are several processes used.
Seed Stratification Methods:
The most natural process is to simply plant wildflower type seeds in the fall. This will allow the seed to undergo the natural cold and wet conditions that soften the seed coat and allow germination to take place. This is one of the best options because it doesn’t interfere with the natural seed cycle process.
Cold stratification is necessary for some seeds to trigger winter like conditions. Strawberries and perennial herbs such as lavender, rosemary, and marshmallow are a perfect example of this. By placing strawberry seeds in the freezer for 30 days before planting you dramatically increase the germination rate of your seed. Some seeds may need to experience freezing temperatures for over a month.
Moist stratification is meant to imitate cold, wet conditions as would be found in a snowy winter. To imitate this your seed can be mixed with inert materials to preserve moisture while kept cool for a few days to months depending on the type of seed. It is important to note that refrigeration should be used, not freezing, for this method. After planting maintain necessary moisture levels.
For seed that requires heat to break dormancy, hot water is the easiest method. Usually those seeds requiring heat also require scarification. Scarification is the physical scratching of the seed coat, commonly with sandpaper. This allows moisture to reach within the seed coat. To stratify soak the scarified seed in boiling hot water until it cools. Drain, and continue with moist stratification for about a month.
If you are having problems with a seed germinating, look into what conditions it would normally experience. Try to mimic those as closely as possible. Nature knows how to take care of itself. If a seed isn’t doing what we expect it to, chances are there is something we are missing from its natural process.