Unlike the seeds of annual flowers, a lot of perennial seeds require a period of cold exposure, or stratification, before they will be able to germinate. This is because in nature, these seeds may be found lying on the ground, buried under heaps of fallen leaves, frost and natural debris. What you may not know is that although the seeds require this to “awaken” in the spring, in nature this process often kills the seeds, which is why the plants are pushed to produce as many seeds as they do.
It is important that the seeds remain cold and moist, as these are the conditions that would occur naturally during the spring in nature with the snow melting.
Each seed that requires stratification is different, so be sure to read your seed packet for specific instructions such as length of time need as well as the required temperature. Your fridge or freezer will do nicely, depending on the temperature that your seed requires.
In order to get your seed ready for the stratification process, be sure to soak your seed beforehand. Soaking them in cold water for 6-12 hours before starting the process can help cut down on the total stratification time needed. This also helps the seed absorb some of the moisture it requires for the chemical changes that will take place.
Here at Pinetree, we plant our seed in peat pots full of a damp mixture of potting soil and worm castings before encasing the entire pot in a plastic bag and placing it it in the freezer. Tying off the plastic bags will trap the moisture inside that is needed for the process to take place.
Once your seeds have spent their required time in your fridge or freezer, you will need to remove them and allow them to sit at room temperature for a period of time before planting them in the ground.
Do not try to cold treat your seeds without first planting them into your preferred medium. The seeds need contact with both air and moisture for the process to take effect. By skipping this step, you may severely damage the seed and cause it to go into a second dormancy, or damage it beyond being able to germinate.
If you live in an area where the temperatures remain between 40°F and 32°F during the winter, you can also cold treat your seeds outside. Place your peat pots on the north side of your house to protect your seeds from drying winds and too much sun, and sink them into the ground to just below the tops of the pots. They will germinate when the weather warms appropriately before you’ll need to plant them.
Here is a list of seeds we offer that require some form of cold stratification: