What Medicinal Herbs Need Cold Stratification? A Beginner’s Guide

March 25, 2025

In this post we'll talk about medcinal herbs that need cold stratification.

As spring rolls around and we feel the excitement of planting season approaching, it's the perfect time to think about expanding our gardens with medicinal herbs. Whether you’re a seasoned gardener or just starting out, growing herbs can be a rewarding experience. However, some require a bit of preparation, especially when it comes to seed starting.

One important gardening technique that every herb gardener should understand is cold stratification. It’s a term that can sound a bit intimidating at first, but don’t worry—we’ll break it down for you in simple terms. In this post, we’ll explore what cold stratification means, which medicinal herbs need it, and how it differs from the needs of your typical vegetable garden.

What Is Cold Stratification?

Cold stratification is a process that mimics the natural conditions that certain seeds need in order to germinate. In the wild, many plants—especially medicinal herbs—experience a cold winter period before they sprout in the spring. This chilling period helps break down the seed coat and allows the seed to “wake up.”

For our farm, we mimic this cold period by exposing seeds to a period of cold and moist conditions before planting them. Think of it as giving your seeds the winter they’d get in nature, but on your own terms! The goal is to help the seed go through a “resting phase” so it’s ready to germinate when the warmer weather arrives.

Why Do Some Herbs Need Cold Stratification?

Not all plants need cold stratification. Some herb seeds can germinate right away without any special treatment, but others need that extended period of cold in order to kickstart the germination process. If you’ve ever tried planting certain medicinal herb seeds only to find that they didn’t germinate (or took much longer than expected), it’s possible that you skipped this crucial step. Though, in fairness, it has been our experience, that getting medicinal herbs to germinate (at least, certain ones) is much more difficult than your tomato seeds from Bonnie’s for example.

Cold stratification is especially important for perennial herbs and certain medicinal plants that naturally grow in regions with cold winters. These plants have evolved to require a cold period in order to trigger germination. If a seed had not evolved to require this a warm Fall day after a mature seed had formed could lead to early germination. I know I see this with various plants, specifically around the vegetable garden. These plants typically have other ways to delay germination or simply produce more seeds than the average medicinal herb to ensure some germination the following Spring.

How to Cold Stratify Your Seeds

Cold stratification is easier than it sounds, and it can be done in just a few simple steps:

1. Prepare the Seeds

Start by collecting your herb seeds. You can find them at your local nursery, online, or even harvest them from mature plants.

2. Moisture

It’s vital that in addition to cold that you add have high moisture content. Place the seeds in a damp paper towel or mix them with a small amount of damp sand or vermiculite. Make sure the mixture is not soaking wet, as this can cause the seeds to rot. Balancing high moisture with not soaking or in water can be difficult. We have found success with an alternate method of opening the seed packet and putting a damp but not sopping wet paper towel in an open ziploc bag within a larger closed tupperware full of our open seed packets. Make sure there are no plastic or moisture-proof layers inside your outer seed packet that would prevent the moisture from permeating.

3. Refrigeration

Place the damp seed mixture in a plastic bag or sealed container and store it in the fridge. Keep it in a spot where it won’t be disturbed, but make sure there’s enough airflow.

4. Timing

Leave the seeds in the refrigerator for the recommended duration, typically between 2-6 weeks, depending on the herb.

5. Planting

After the stratification period is complete, you can plant your seeds in a prepared garden bed or container, depending on your preference.

Medicinal Herbs That Need Cold Stratification

Before adding medicinal herbs to your garden take a look at the below list and make sure that you stratify for adequate time to ensure a healthy germination this season. Keep in mind that the exact duration of cold stratification can vary from plant to plant, but the general process remains the same. In general stratifying for a longer period of time will have a beneficial impact and in no situation I can think of will there be a negative impact to stratifying for longer.

Here’s a list of some popular medicinal herbs that require cold stratification:

1. Echinacea (Echinacea purpurea)

Echinacea, ( we grow echinacea purpurea in addition to narrowleaf echinacea or echinacea angustifolia) also known as purple coneflower, is one of the most beloved medicinal herbs, known for its immune-boosting properties. It needs a relatively long period of cold stratification to encourage seed germination. For best results, Echinacea seeds should be chilled for 3-4 weeks in the refrigerator before planting them outdoors in the spring. Echinacea can also be a slow germinator so be patient with it.

2. Milk Thistle (Silybum marianum)

Milk thistle is a well-known herb for liver health, and like Echinacea, it requires cold stratification to germinate. The seeds should be placed in the fridge for about 30 days before being planted. Milk thistle can be invasive so be careful where you plant it. We haven’t tried growing milk thistle on our farm yet (but would love to) and are far enough North that the plant would most likely die in winter so it is on our list to try some day. I do consume milk thistle most days and love the herb.

3. Black Cohosh (Actaea racemosa)

Black cohosh is used for its hormone-regulating and anti-inflammatory properties. Its seeds are notorious for being hard to germinate without cold stratification. A 4-6 week chilling period is ideal to give these seeds the best chance of sprouting.

4. Ginseng (Panax ginseng)

Ginseng is another famous medicinal herb, renowned for its adaptogenic and stress-reducing benefits. Ginseng seeds need to go through a cold stratification process to break dormancy. Typically, Ginseng requires about 60 days of cold stratification. It’s a slow-growing plant, but with patience, you’ll be rewarded with this powerful herb in your garden. Ginseng can be notoriously hard to grow even with proper instructions so a proper dose of luck is probably in order. We’ve done a number of test plots on our farm but have sadly not had success with germination. And we won’t tell you if we ever do succeed as the value of this root makes it prone to theft :).

5. Astragalus (Astragalus membranaceus)

Astragalus, a staple in traditional Chinese medicine, is known for its immune-boosting properties. These seeds require cold stratification for about 3-4 weeks in a refrigerator or outdoor cold frame before they can germinate. We are growing this one for sale for the first time this year. It’s not in the online shop yet as we won’t have any to sell this year. For a full list of what we are planting this year, see our post here.

6. Valerian (Valeriana officinalis)

Valerian, widely used as a natural remedy for anxiety and sleep disorders, also benefits from cold stratification. A 2-3 week period of cold and moist conditions is generally sufficient to trigger germination. Just be sure to keep the seeds slightly damp during the chilling process, and they’ll be ready to plant once the weather warms up.

8. Wild Ginger (Asarum canadense)

Wild ginger, with its anti-inflammatory and digestive benefits, is another herb that requires cold stratification. The seeds need to undergo 30-60 days of cold treatment to improve germination. This herb grows naturally in shaded, woodland environments, so a cool, moist chilling period is essential for successful growth.

9. Catnip (Nepeta cataria)

While many people think of catnip as just a fun herb for pets, it also has medicinal benefits, such as promoting relaxation and easing digestive issues. Catnip seeds need cold stratification for about 3 weeks. You can easily replicate this process by placing the seeds in a sealed plastic bag with some damp sand in the fridge.

10. Marshmallow (Althaea officinalis)

Marshmallow, known for its soothing properties for sore throats and coughs, also benefits from cold stratification. The seeds should be chilled for 3-4 weeks in the refrigerator before being planted in the spring. This helps the seeds overcome their dormancy period and ensures a higher germination rate. If you don’t stratify in time or don’t get your marshmallow planted, you can buy dried marshmallow root or aerials direct from us.

How Does Cold Stratification Differ from Vegetable Garden Needs?

If you’re used to gardening with vegetables, you might be wondering how cold stratification differs from your typical gardening practices. Vegetables like tomatoes, peppers, and beans don’t require cold stratification—they generally germinate well in warmer conditions. Instead, vegetable seeds often need a warm, consistent environment to sprout.

Medicinal herbs often follow natural growth cycles that are influenced by environmental factors like temperature and moisture.

It’s outside of the scope of this article but other treatments seeds require to germinate include scarification ( physically nicking, sanding or scratching ), photoblastism, both positive (see tulsi) and negative (requirement for light or dark to germinate) smoke or fire (self-explanatory) endozoochory (passing through digestive system). Moreover, Inoculation (is not necessarily required to germinate but can significantly improve germination rates.

Alternatives to Stratification

If you don’t have time to wait the prescribed duration an alternative method to stratifying or scarifying your seeds is to use a gentle acid to break the dormancy. We have tried this with mixed success but will reserve too much content until we’ve gained a bit more expertise. We use the refrigeration method which we believe has a lower margin of error and higher success rate if you start early enough.

Conclusion

Cold stratification is an essential technique for anyone looking to grow medicinal herbs from seed. Understanding which herbs need cold treatment—and how to apply it—can make the difference between a successful, thriving herb garden and one that doesn’t quite take off. As spring approaches, take the time to plan ahead for your medicinal herb garden, and remember that patience and preparation are key.

By growing herbs like Echinacea, Milk Thistle, Marshmallow, Ginseng, and others that require cold stratification, you’re not only enriching your garden with beautiful, healing plants but also preparing for a season of wellness and self-sufficiency. Happy gardening!

Didn’t get around to buying your medicinal herb seeds in time to add them to your garden this year. Check out our full collection of herbs we grow, dry on farm and ship direct to our customers for maximum potency and freshness.

Back to blog