How to Cold-Treat Cranberry Seeds

Determine how long your seeds require stratifying. Garden centers or your local cooperative extension office can assist you if you're not certain. The process normally takes several months. Seeds of some cranberry species require double-stratification and need a warm period between two cold periods. The first cold period encourages root formation; the second encourages the plant's first true leaves to appear to begin photosynthesis.

Store seeds cold, such as in an refrigerator, until you're ready to begin the stratification process. Keep in mind the fresher the seed, the better the results. When you're ready to start the process, allow the seeds to warm to room temperature. Then soak them in room-temperature water for 12 to 24 hours.

Drain the water and place seeds in a plastic bag. The F.W. Schumacher Co. recommends using a plastic bag that holds a volume three to four times greater than the amount of seed. Add milled sphagnum moss or vermiculite to the bag. Spray seeds with a fungicide to help protect against mold.

Add water to the bag in a uniform manner, and allow the growing medium to soak it up; moss may take eight to 10 hours. Then hold the bag upside down and twist the bag to remove excess water, until no more runs out. Excessive moisture causes mold. Write the name of the seed, the date stratification began and the date it should end on the bag.

Shake the bag and place it in the refrigerator, to keep the bag at approximately 34 to 41 degrees Fahrenheit. It can also be stored in an unheated garage or anywhere that's cold, but remains above freezing. To help prevent mold, check the bag the next day for any standing water and pour out. Also check the bag every few days to ensure the medium is moist and hasn't dried out. If it is dry, add water, but just enough for the medium to be moist, not wet. Remove any seeds that become moldy.

Remove the seeds when the species' time requirement for stratifying is met. The F.W. Schumacher Co. advises removing them after 20 percent have germinated -- and then planting them immediately, whether they've germinated or not. The University of Arizona Master Gardener's Manual stresses that stratified seeds be handled carefully, especially if small roots and shoots have emerged. If they have emerged already, ensure you don't break them off or cause injury to the seed coats, as doing so could cause disease to occur.