How to Cold Stratify Seeds

Most perennial seeds need to be cold stratified, or chilled, before planting, to increase the chance of germination. Cold stratification mimics the seasonal effect of winter before spring germination. When you cold stratify seeds indoors, follow these steps and allow 3 to 8 weeks for chilling before spring planting.

Plant your perennial seeds in the garden in the fall if you wish to cold stratify them outdoors. Outdoor cold stratification is more risky than indoors and often leads to a lower germination rate. Seeds planted in the fall to cold stratify naturally are often exposed to extreme temperatures, too wet or too dry of any environment, or being eaten by birds or rodents.

Wrap your seeds in a moist piece of paper towel and place them in a plastic bag if you want to cold stratify them in the refrigerator. The paper towel should be damp, but not dripping wet. Seal the plastic bag and put it in the refrigerator for the winter.

Use a damp, sterile medium such as vermiculite or peat moss instead of paper towel as an alternative method of cold stratification. Again, make the medium damp, but not wet, and seal it in a plastic bag before placing in the refrigerator.

Label and date your seeds when cold stratifying them, so you remember which seeds are which when it comes time to plant them. It is also a good idea to mark your calendar for spring planting time so you remember to take them out of the refrigerator and plant them.

Check your seeds every couple of weeks during cold stratification. Make sure the paper towel or medium is still moist and look to see if any of the seeds have begun early germination or are molding. Remove and discard any seeds that are showing signs of molding. If the seeds are showing signs of early growth, they need to be discarded or planted.

Remove your seeds from the refrigerator at planting time and plant them in the garden immediately. Do not allow the seeds to dry out before planting.

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