Growing wildflowers and herb seeds successfully requires an extra step for maximum germination rates — stratification.
What is seed stratification and how does it improve germination rates?
Many wildflower and herb seeds have extra thick seed casings to prevent them from sprouting too early in the spring. If you want the best possible germination rate, then stratify the seed casings before planting using one of these 3 methods.
The 3 Types of Stratification
- Cold Stratification — a period of cooling at near freezing temperatures to “damage” the seed casings. This can be accomplished by artificially mimicking winter conditions, in the fridge on a damp paper towel. Or it can be done by simply planting in pots outside during the winter, direct sowing seeds in the late fall, or planting on the ground under snow.
- Scarification — scratching up the seed coating with sandpaper or other rough surface
- Soaking — 12-24 hour soak in cool water will soften the seed casing
Wildflower and herb seeds also naturally germinate irregularly, a few at a time, to make sure that if the first sprouts are wiped out by a frost, the later sprouts will survive.
Morning Chores has a great article on various ways to do seed stratification. I usually just put them in pots on my front porch around mid winter. Some plants, like those in the mint family, I bring in after a few days. Other plants like violas and chamomile will remain outside to sprout and grow until they need to be potted up.
Which seeds’ germination rates will cold stratification boost?
Many seed packets neglect to mention that germination rates can be significantly improved by stratifying seeds before planting. So how do you know which seeds benefit from cold stratification?
I tried searching online for a comprehensive list of seeds that benefit from stratification, but most of the information about stratification was spread around on various seed company websites. I created these charts to summarize all the types of seeds whose germination improve significantly after cold stratification and what were the recommended stratification time/methods.
Don’t be caught off guard by a seed packet that suggests cold stratification for a a couple months before planting. Check the chart and your seed packets today!
Download this free printable chart!
There are 4 pages and they can be printed 8.5 x 11″ or half sheets double sided to make a little booklet, as I did for my planner.