Struggling to get certain seeds like Olive Tree or bonsai seeds to germinate? Seeds like these that normally go through an overwintering process require something called stratification in order to jumpstart germination. Let's jump in!
What is Seed Stratification?
Seed stratification is a process that involves exposing seeds to specific conditions of moisture and temperature to encourage germination. This mimics the natural cycle that seeds would go through in the wild, where they would experience a winter with cold, moist conditions before spring, when the seeds get the green light to start germinating.
By replicating these conditions, gardeners can improve the germination rate of certain seeds. There are 2 different types of stratification, dry and wet stratification.
Dry Stratification
Dry stratification involves storing seeds in a dry environment at a specific temperature for a period of time.
Seeds that require dry stratification are typically those from plants that grow in arid or dry climates, and have evolved to withstand harsh environmental conditions such as drought. These seeds need a period of dry, cool conditions to break dormancy and germinate. Without this period of dry stratification, the seeds may remain dormant and not sprout. Examples of seeds that need dry stratification include lavender, sage, and many wildflower species.
Wet Stratification
On the other hand, wet stratification involves keeping seeds moist or even submerged in
water for a period of time. This process helps to soften the seed coat and kickstart the germination process. Seeds that need wet stratification are typically those from plants that grow in moist or wet environments. These seeds require a period of moist, cold conditions to break dormancy and germinate. By exposing these seeds to cold, moist conditions, it mimics the winter season when the seeds would naturally be in the ground.
Examples of seeds that need wet stratification include many tree species like oak and maple. (Reference our seed prep guide for a list of our seeds that need stratification or other seed prep steps)
How to Stratify Seeds
1. For dry stratification, keep them in their original packaging and skip to step 2. For wet stratification, start by placing your seeds in a damp paper towel or in a container with moistened soil or peat moss.
2. Seal the seeds in a plastic bag or container to maintain moisture levels.
3. Store the seeds in the refrigerator for a specific period of time(usually about a month), depending on the type of seed. This cold, moist environment will simulate winter conditions.
4. Check on the seeds periodically to ensure they remain moist but not waterlogged.
5. After the stratification period is over, plant the seeds in the usual recommended setup outlined in our planting guide.
As an easy alternative, if you're planting the seeds during the middle-end of winter, you can plant the seeds in a sealed container like a mini greenhouse and leave them in a cold, unheated room such as a garage, or outdoors so they can experience a natural overwintering process. Happy planting!
