Many wildflower seeds have a dormancy built into them which prevents germination. In Nature this dormancy protects seeds from germinating as soon as they fall on the ground. For example, if they were to germinate in September, the seedlings would not be big enough to make it through the winter.
There are two ways to achieve cold moist stratification:
Method 1: The best method for breaking dormancy is to plant the seed between December and February. A benefit of winter planting is freezing and thawing, and rain works the seeds into the soil, establishing seed to soil contact. This causes the seeds to imbibe water and germinate when the temperature is warm enough.
Method 2: The following process will help to break dormancy in wildflower seeds when planting later in spring is the only option.
1. Place seeds in a plastic bag & label the outside with the date and species name. Use a nylon weave bag for larger quantities, leave room for swelling.
2. Cover with water. Let soak for 4 hours.
3. Poke pin holes in the bottom of plastic bag to drain excess water. Be careful not to lose small seeds, but there should be no visible water in the bottom of the bag.
4. Mix seed with an equal amount of pearlite, in plastic bag.
5. Store in the refrigerator 4 to 5 weeks, then plant.
6. Check weekly for germination or molding, if either occurs, plant as soon as possible. Also check the moisture, if dry, add a small amount of water.
7. If possible, after planting, water area twice a week for two weeks then once a week for a month if no rain falls. For the remainder of the growing season, water when it is unseasonably dry.
Method 2 is not foolproof. Method 1, Mother Nature’s way of breaking dormancy, is more reliable than anything we can do. If planting seeds in late February or early March, do steps 1,2, and 3. Store seeds in refrigerator and try to plant within a couple of weeks, ideally before a rain or a watering.