Stratification or pre-chilling may be required to break dormancy for hard-to-germinate plants, i.e. trees, especially nut trees, or shrubs. For plants that expect two winters before germinating, a double dormancy, a double treatment is required. The easiest way to grow these is to sow them in the fall, ideally in a cold frame for protection and easier observation; let one or more winters pass.
Alternatively, in early winter, mix seeds with builder's sand or some other sterile, well-draining medium and place in clay flowerpot, or perforated plastic pots, and set outside in protected location. When snow clears, empty the pot, and sow swollen seeds either inside or out.
A sterile, moist growing medium may be used for the above technique. Check daily for germination in spring and move to warmer area when this happens. Again, transplant with the first or second set of true leaves.
Where cold winters just don't happen, use the fridge. Mix seed with 2 to 3 times the amount of damp peat moss, damp sand or other sterile medium, and seal well in a plastic bag, leaving plenty of air available. Leave at 60-65F/15-18C for several days then place in the fridge. Check frequently for germination. Keep damp. This treatment may have to be repeated after a warm treatment, with double dormancy.
When any seeds germinate, pot them all. Note that germination can take years, even after stratification. Don't give up hope and don't throw out your seeds.
Some seed may germinate equally well if chilled in the freezer for half the time. However, do not ever commit a significant amount of seed to this, or any other technique, you have not used before.
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