Do you struggle to get perennial herb, flower, and vegetable seeds to germinate? Even though growing annual vegetables is a breeze?
I had this happen to me when I first started gardening. I could grow nearly any vegetable from seed. But my seed starting trays of certain herbs would remain totally ungerminated.
For example, I bought 4 packets of nettle seeds and tried everything (or so I thought) to get them to sprout to no avail.
It took me a while to realize that I was primarily having difficulty with perennial seeds.
Once I discovered cold stratification, my seed starting failures made sense. The internal clocks of the seeds weren’t triggered to sprout from the warm environment I was giving them. They needed a bit of a winter’s chill to orient them first.
Learn about cold stratification so you can grow a wider range of plants! The knowledge that I share with you below will maximize the potential of your garden.
In this guide, you'll learn:
1. You'll notice that most plants in our cold stratification list are perennial plants.
Typically annual seeds like broccoli, nasturtiums, or calendula don't need cold stratification.
2. Plants developed a need for cold stratification due to their natural growing conditions.
These seeds underwent cold stratification naturally during winters in their native habitats.
Cold stratification is an adaptation that plants developed to increase their survivability. If seeds drop in autumn but experience warm temperatures, they could sprout. This would be detrimental to the plant, because it would die during the cold winter months.
Instead, the seeds have a need to experience a period of cold before they germinate. This means they are more likely to sprout at the right time in spring and survive.
So, two things to think about when wondering if you need to cold stratify seeds are:
If the answer to both of these questions is "yes," then it's likely that the seeds will germinate better if cold stratified. If your unsure, keep scrolling to see a complete list of seeds that need cold stratification.
Seeds can be stratified in a few ways, with certain techniques working best for each plant.
1. Cold Only:
Place seed packet or the number of seeds you want in another small bag. Place the bag in the refrigerator or freezer for a specific length of time.
This method obviously requires the least effort. It is also helpful for seeds that will need light to germinate. This is because you can ensure that the seeds aren’t covered by soil later on.
2. Cold + Moist:
Wrap seeds in a moist paper towel and place that paper towel in a bag of some sort. Then place this in the refrigerator or freezer
This method gives the seeds the extra benefit of the water, which may help their success rate. It also makes it easier to pick out the seeds and surface sow if they need light to germinate.
3. Cold + Moist + Soil:
Mix seeds with a moist soil mix of some kind. Wrap in scrap fabric, paper towel, or place in a ziplock bag. Place this in the refrigerator or freezer.
This method requires the most labor. However, it gives you the benefit of more water retention than the paper towel method. If the seeds are very small, it can be difficult to sort them out in the soil to know how many you’re planting or to surface sow.
4. Fall sowing:
Plant seeds in the fall to create a natural cold stratification period for plants. This works in areas that experience cold winters. Make sure to label where you sowed your seeds so that you know where they are in the springtime!
I created the spreadsheets below when I was planning out a large new flower garden. I became frustrated because I had to research the cold stratification needs of each plant individually. It was difficult to keep track of everything.
Since I’m a huge plant nerd, I made a spreadsheet of all the information. I have divided the information up into categories below.
This list of plants that need cold stratification includes:
- the length of time that the seeds need stratification
- if the seeds need light to germinate
- if the seeds need to be scarred before planting
- optimal starting dates for the whole process
Note that these optimal dates are for zone 7-ish. You might need to shift things ahead or behind based on your last frost date.
This information is based on a last frost date of April 21st
As a guide,
4 weeks before this last frost is March 21
8 weeks before this last frost is February 21
10 weeks before this last frost is February 7
Avoid these common cold stratification issues that can come up as you're learning:
1. Label your seeds with:
This helps to make sure that each seed experiences cold for the necessary amount of time.
2. Set calendar reminders on your phone. Add in each end date of your seeds in cold treatment, so that you have a reminder of when to sow each one.
3. Check the moisture level of your seeds during the cold stratification process. If required, seeds should be moist during the duration of treatment, but not too wet.
4. If you are practicing cold stratification by sowing seeds in the ground in fall, mark the areas where you sowed your seeds. It can be hard to remember not to plant in that area come spring!
5. Be sure to reference if the seed needs light after cold stratification. If it does, sow the seed on the surface of the soil and do not bury it. This will help increase germination rates.
Cold stratification is necessary for beautiful flowers and herbs to germinate in your garden. While it takes some extra time and planning, it's totally worth it.
Hopefully this guide helps you integrate cold stratification into your seed starting routine.
Whether you're a beginner or seasoned gardener, these guides I've created might help you find even more success in your gardening adventures:
Starting Seeds Indoors: Get a head start on the growing season with my full guide on starting vegetables from seed - plus common mistakes that beginners make and how to avoid them.
Book List for Beginner Gardeners: My must-have list of books for new gardeners - get ideas for what to add to your gardening library.
Perennial Power: A full database of perennial crops, with guides on which edible perennials will grow in your growing zone. Plus, sort by light and water requirements. A great list for anyone looking to get started with classic or unusual permaculture perennials.
