Vermiculite is a mineral composed of flakes that can range in size from very tiny to quite large. Nurseries sell vermiculite commercially as a soil amendment and when you add it to soil, vermiculite provides aeration and drainage. Because vermiculite provides a sterile medium, it is often used, either alone or mixed with peat moss, as a seed starter.
For Seeds That Require Cold Moist Stratification
Stratification is the process of subjecting seeds to both cold and moist conditions. Typically, temperatures must be between 1°C and 5°C (34°F and 41°F).
1. Use three times the amount of vermiculite as seeds. It is important to only slightly dampen the vermiculite, as excessive moisture can cause the seeds to grow mouldy in the bag.
2. Add the seeds to the vermiculite and seal the bag.
3. Place the bag into the refrigerator for the prescribed amount of time.
4. After undergoing the recommended period of stratification, the seeds are ready to be removed and sown in the nursery bed for germination. Alternatively, the seed may be sown in small pots filled with moist soil and then the whole thing enclosed inside a plastic bag before placing inside a common refrigerator.