Seed Stratification: Cold Treatment Indoors

• Posted on 19 December 2024
• By The Biologic Team
• 0

Have you ever struggled to get certain seed verities like milkweed, lupine and lavender to germinate? While this could be due to a variety of factors such as incorrect soil moisture, seed viability, soil temperature or planting depth, not all seeds are ready to sprout as soon as they are planted in soil. For some seeds, dormancy caused by a physical barrier in the form of a hard or waxy seed coat requires exposure to a period of cold, moist conditions to be broken. This process of cold-stratification breaks down the exterior seed coat and allows the seed to germinate and sprout.

Many types of wildflowers, perennials, shrubs, and trees produce seeds that must undergo a cold period for some amount of time for seed germination to begin. Generally, native plants grown in cold climates will require cold stratification before you plant them in the early spring.  Some popular plants that require stratification include many of the Milkweed species, Purple Coneflower, False Indigo, Black-Eyed Susan, Flowering Dogwood, Redbud, and many others. Many times, seed packets will let us know if there is a cold period requirement for germination, but it is always a good idea to research any germination needs; especially when it comes to collecting and saving seeds.

How to Stratify Seeds in the Refrigerator

Follow these steps to cold stratify your seeds in the fridge.

1. Place the seeds in a damp medium. Small seeds can be sprinkled onto a damp paper towel. Larger seeds should be placed in a moist medium such as peat moss or vermiculite. Ensure that the medium is moist but not soaking wet.

2. Store the moist seeds in a plastic bag. Once your seeds are wrapped in a damp paper towel or planted in a moist growing medium, place them in a plastic bag. To prevent excess water from accumulating inside the bag, allow for some airflow by leaving the bag partially open or puncturing the bag with a few small holes.

3. Place the bag in the fridge. Most seeds require about a month of cold stratification to increase germination rates. However, the exact amount of time needed for the stratification process will vary depending on the type of seed you choose. Consult the cold stratification timeframe suggested on the seed packet. Check on your seeds periodically and if they start to sprout, remove them from the bag and plant them.