What is Seed Stratification?

Have you ever had difficulty getting certain seeds to germinate? It could be that they need cold stratification before planting, for success. Not all seeds need the same conditions to encourage germination. Some need warm, moist weather, while others need a cold period. Many plants that are native to climates with cold seasons require a period of cold temperatures to break their dormancy and initiate the germination process. 

What is cold stratification?

Stratification happens naturally over the winter. The fluctuations in the weather trigger both the dormancy and the emergence from that dormancy, so the seeds know when the season is right to grow.

Which seeds need stratification?

• Artichoke

• Mint

• Chamomile

• Coneflower

• Catnip

• Echinacea

• Hops

• Lavender

• Marigold

• Milkweed 

• Perennial sweet pea

• Sage

• Rosemary

(This is not a complete list)

How do I stratify seeds?

The easiest way to cold-stratify your seeds in a moderate to cool climate is to plant your seeds in the fall. By planting in the fall, they will experience natural cold stratification without the gardener having to do much work. If you live in a warm climate, you’ll need to carry out the process artificially. 

Artificial cold-stratification is typically done using a refrigerator at a temperature between 33°-40°F. It is done wet or dry, depending on the type of seed. In general, if the seed grows naturally in an arid climate, it must be kept dry for this process, and vice versa.