Seed stratification

Some tree, shrub, and perennial seeds remain dormant until they experience the seasonal conditions that signal a suitable time to germinate. Cold, moist stratification gives hydrated seed a controlled period of cool conditions before sowing.

Start with the packet requirement

Stratification needs vary by species and can also vary among seed lots. Use the cold or warm sequence and duration printed on the seed packet or stated in the product description. A duration is a practical target, not a promise that every seed will germinate at once.

Outdoor stratification

Sow seed in a labelled pot, nursery bed, or other well drained container and leave it outdoors through the required season. Protect the seed from rodents and make sure the container can drain. This method lets natural temperature changes provide the treatment.

Refrigerator stratification

Mix the seed with a clean medium that is moist but not wet, place it in a labelled container or bag, and refrigerate it at about 1 to 4 C. Do not use a household freezer. Check the seed periodically for excess water, drying, mould, or early root growth.

When the required period is complete, sow the seed using the depth, light, and temperature requirements for that species. If a root begins to emerge in the refrigerator, handle it carefully and sow it promptly.

Warm cycles and scarification

Some species require a warm period followed by cold, or more than one seasonal cycle. Others have a hard seed coat that must be scarified so water can enter. Follow the product specific instructions rather than applying either treatment to every seed.