Cold Stratification of Seeds - Why & How

How do you know if you need to use cold stratification for your seeds? And if so, how do you do this? I’m sharing both why and how to cold stratify your seeds for better germination and production.

This is exactly what we’ll be discussing in this post. I just started planning the expansion of my medicinal herb garden and some herbs require cold stratification for proper germination.

I have an entire guide on how to start seeds indoors, but quickly realized I didn’t have information about cold stratification on my website so this is the post answering the question of why and how to do cold stratification.

Table of Contents

What is Cold Stratification?

Cold stratification is putting seeds into a dormancy state with temperatures below 40° Fahrenheit for a specific period of time in order to improve the germination rate (the number of seeds that will sprout).

This needs to be done with specific perennial and biennial herbs and flowers when trying to grow them from seed indoors (see list below for flowering herbs).

In nature, these seeds won’t sprout without the cold period because if they did sprout early (right before winter) then they would die, so this cold period which signifies winter, allows them to sprout in the spring when temps warm up without the danger of winter freezes killing them just as they’ve sprouted.

A woman putting ziplock bags of seeds into the refrigerator for cold stratification.

How Long is Cold Stratification?

This is dependent on the seed type. Some only require a few weeks whereas some require up to four months in the refrigerator.

You should be able to find this information with a simple search on the internet, or on the seed packet itself.

Two small ziplock bags with wet paper towels inside.

Two small ziplock bags with wet paper towels and seeds inside.

Dry vs. Moist Stratification

Most herbal seeds need moist cold stratification, which is what I demonstrate in the video where I walk you through this exact process inside the Pioneering Today Academy (I only open the Pioneering Today Academy a few times each year, click the link to get on the waitlist for the next time doors open!).

The exception to this is dessert plants that just require time in the cold temp but without moisture (in nature the area they hail from wouldn’t have snow or rainfall).

A woman in a kitchen placing a paper towel into a ziplock bag.

A woman in the kitchen spooning water onto a paper towel.

How to Moist Stratify Seeds

I prefer to use a paper towel inside a Ziplock bag. They don’t take up a lot of room and make a great little greenhouse environment. It’s cheap and you can reuse the bags again and again.

Fold the paper towel in half (make sure it fits inside your bag, most paper towels are fairly uniform in size) and place it inside the bag.
Use a spoon and begin wetting the towel from the center out, stop adding water when the upper ½-1 inch from the corners of the towel are still dry (the water will continue to spread out).
Scatter your seeds in the center of the towel.
Press them down with your finger to get them into the water.
Close the bag, leaving a ½ inch opening on one end for air flow.
Label bag with seed name and date.
Place in the fridge.
Check periodically that seeds aren’t drying out.
Leave in fridge for 4 to 6 weeks (some seeds only require 3 weeks like Marshmallow but others may require extra time).

How to Plant Germinated Seeds

Once your seeds have gone through the cold stratification process they’ll be germinated and ready for planting.

Simply take one of the germinated seeds and place it into your prepared seed starting soil and continue as you would with seeds you started indoors by direct sowing.