Certain seeds will not germinate until they have been subjected for some weeks or even months to low temperatures and humid conditions similar to those which occur in nature after they drop from the parent plant and are covered with fallen leaves and other forest debris.

To simulate this natural winter environment, gardeners employ a technique called stratification. A usual method is to fill a wooden box with alternate layers of seeds and moist sand, or sand and peat moss and then to bury the box 6 in. deep in a well-drained, shaded location outdoors.

Fleshy fruits-such as those of holly, cotoneaster and hawthorn are stratified without removing the pulp that surrounds the fruit they contain. As a precaution against mice and other rodents, it is wise to enclose the box in fine wire mesh. When very small seeds are being stratified they may be spread between layers of cheese-cloth before they are buried in the sand, to make finding them at a later date easier.

An alternative method is to stratify seeds by " mixing them with slightly moist sand, or a mixture of sand and peat moss, and keep the mixture in closed - but not completely airtight - jars in a refrigerator. Temperatures of 1 to 4.5 C. are satisfactory for most seeds requiring stratification.

Most seeds stratified in autumn will germinate the following spring, but some kinds - for example hollies - do not germinate until the second spring after they are stratified. When the time for germination arrives,
the seeds should be separated from the sand or sand and peat moss by sifting or by hand picking. They should be sown in pots, pans, boxes, cold frames or directly outdoors.
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