Some seeds need a winter nap.
They sprout only after a period in moist, cold soil.
The process is called stratification. Read more abut it HERE.
Most trees, shrubs, and many perennials like to go through the winter as seeds
. In nature, they drop from the plant, spend the winter in cold wet soil, and sprout in spring. If you plant in pots in the fall and leave them outdoors, they will sprout when the weather warms.
If you want to plant in summer, you can use the refrigerator to provide the cold.
Domesticated vegetables and grains have had this trait bred out of them, so the farmer can control when and where they sprout. But many wild plants need stratification, as do most temperate-climate trees, shrubs, and perennials. (They have learned not to sprout too soon, so the young plant doesn't
freeze. ) You need to give the seeds enough cold time to meet their
chill requirement--which is listed for each variety.
Wildflowers from mild climates like to sprout in fall and overwinter as small plants.