Trying to sow and germinate native milkweed seeds can be very frustrating if not done properly. Many native milkweeds need to experience the conditions of winter and then the warmth of spring in order for them to germinate. Without this cold period, seeds may not germinate or may germinate poorly, so cold stratification is often a crucial step when growing these plants in areas where winter conditions differ from their native habitat. Or, when trying to germinate seeds outside of the current outdoor season.

Milkweed plants and seeds are winter dormant. Without experiencing cold temperatures followed by warm temperatures, the seeds will remain dormant. Most native milkweeds require this cold period. Asclepias perennis is one of the few exceptions.

So how can we have luck germinating milkweed seeds?

The first and easiest option is to collect seeds throughout the summer and then store them in a dark dry location outside. Some people suggest a dark and damp location for milkweed seeds. You can try both, but we have found dark and dry works well better. Asclepias incarnata and Asclepias perennis do generally benefit with some moisture during the cold stratification process. By storing outside, the seeds will experience temperatures exactly as they would had they fallen to the ground. Then, in the spring you can sow the seeds and allow them to experience warmer temperatures in the seed tray or whatever you sow the seeds in.

The second option is to mimic the outdoor temperatures by cold stratification in a fridge. This process is what the rest of this forum will be focused on.

If you are looking for general information on Cold Stratification, go over to our Forum Category "Questions and Answers" and find our "What is Cold Stratification?" post. Or, you can CLICK HERE.

How to Cold Stratify Seeds

Here’s a basic step-by-step guide to help you get started with cold stratification of milkweed seeds. *Please note* this guide is based on information gathered from credible online resources. We have interjected our own opinions in as well, typically after the guidance found from the online resources. So, some information may contradict itself. A list of websites used for this information can be found at the bottom of this post.

1. Choose the right seeds for your area: Better results come from seeds that are from native plants found as close to your area as possible. You should at least be looking for an ecotype local to you. That way, the seeds are going to be successful with your area's normal weather, seasons, temperatures, soil conditions, precipitation conditions, etc. We recommend searching in this order: Seeds from plants found in your:

   Neighborhood

   County

   Region within the state

   State

   Region within the U.S.

2. Prepare the Seeds: Some seeds need to be cleaned of any surrounding fruit or debris before stratification.

   Check if the seeds need to be scarified (lightly scratched or nicked) to allow moisture to penetrate the seed coat before the cold stratification process begins. This may be necessary for some milkweed species. We have found that the majority of FL native milkweed seeds do not need to be scarified.

   There are several recommendations to soak the seeds for 24-48 hours prior to cold stratification. We have not found that this is a necessary step.

3. Moisture and Medium: Place the seeds in a slightly damp material like sand, peat moss, or paper towels. The medium should be moist, but not soggy. For many seeds, a mix of damp sand works well, as it allows air circulation while maintaining moisture. *Please note* there are many gardeners out there who find that they have better germination rates with dry storage instead of damp storage. We recommend trying both and determining which one you have better results with and continue to experiment. Our opinion on the two methods is that Florida typically experiences dry cold seasons and therefore, we generally see better success with dry mediums that we occasionally lightly mist once per week.

4. Refrigeration: After preparing the seeds, place them in a sealed plastic bag or container. Ensure it’s airtight to prevent drying out. This is not necessary for dry storage and we have found that air flow is generally better for most species.

   A period of 30 to 90 days is typical, but FL native milkweed seeds can generally be ready after 2 weeks. A longer period of 30 days will not hurt the seeds.

5. Monitor Moisture Levels: During the stratification process, it’s important to keep checking the moisture levels. If you notice the medium is drying out, lightly mist it to maintain optimal conditions. This is not necessary for dry storage.

6. Planting After Stratification: After your pre-determined cold period is over, remove the seeds from the fridge and sow them in your prepared soil. Place the milkweed seeds in 1" to 4" deep seed trays or small pots with a medium recommended for the species. For example, swamp (Ascl. incarnata) and aquatic (Ascl. perennis) milkweeds will prefer moisture for germination and overall health. Whereas other species may prefer dry mediums - such as Asclepias tuberosa. Place seeds at the top of the medium filled area and then lightly cover seeds with medium. Some online resources suggest sowing the seeds 3/4" deep. We have found better success with seeds on top of the dirt and only a sprinkle of medium on top. Just enough medium to cover the seed from being exposed to direct sunlight.

   Watering seeds is best done from the bottom up, if possible. The tray or pot needs to be able to drain, so this can be a tricky process.

   Germination rates are best if seeds are sown in areas with plenty of sunlight.

7. Germination: Most milkweed seeds will germinate in 10-15 days after sowing. But, they generally can take up to 21 days. If you sow seeds outdoors too early, they may even take up to 45 days.

   Once seedlings have emerged, you can help retain moisture in the pot with a light mulching.

Extra Tips:

Labeling: Since many seeds have different cold stratification requirements, it’s a good idea to label each bag or container with the seed species and the date you started the process.

Skip the Chill: Cold stratification usually needed for milkweed seeds. You may find that some FL native milkweeds don't necessarily need the cold temperatures to germinate. But, we have found that the germination rate does increase with incorporating it into your process.

Experiment: Try multiple methods and see what you find works best. Different methods may work for different regions, even within the state of FL. If you do not source your seeds close to your region, you may have to alter your methods that mimic the ecotype of the seeds you have.

Determine Your Sowing Dates Ahead of Time: Find the recommended sowing dates for your region. Then, backwards plan for when you need to start the cold stratification process. For example, if your seeds need to be sowed in May, you should begin the cold stratification process based on the length of of time you plan on using for cold stratification.

We have success in Central Florida with sowing seeds in March - May. Seeds can also be sown throughout summer but we recommend no later than August. Plants will need time to establish a healthy root system that will enable to plant to survive dormancy.

Protection From Pests: While many gardeners are planting milkweed for butterflies, seedlings will need some protection from butterfly larvae so they have enough time to become established. We recommend protecting seedlings until they are over 12 inches. That way they will likely return from the heavy appetite of butterfly larvae.

Other pests include oleander aphids and milkweed bugs.

If you’ve had success or failure with cold stratification, or if you have tips of your own, I’d love to hear about your experiences! Let’s chat about all things cold stratification and seed germination.