Cold Stratify Milkweed Seeds to Increase your Germination Rate
Most milkweed species planted in North America need a cold moist stratification to encourage spring germination. Cold moist stratification is a technique used to simulate the real-world conditions a seed would receive outdoors after the frozen winter gives way to a warm, wet spring.
We haven’t started many native seeds indoors because we’ve been the lucky recipients of a magnificent common milkweed patch, compliments of Mother Nature.
When we have started native seeds indoors, I’ve simply put the seeds in a plastic bag, then placed them inside a refrigerator for about a month. I’ve never had a problem starting common, swamp, or butterfly weed seeds in this manner, but have only done this on a small scale so I’m uncertain how effective this is compared to a cold moist stratification.
Today, I’m here to conduct an experiment that might shed some light on what the most effective stratification method is for milkweed seeds. These are the first simple steps for milkweed cold stratification…won’t you plant along?
WET Cold Stratification VS DRY Cold Stratification
1. Gather your supplies
Native milkweed seeds, coffee filters or paper towels, plates, plastic sandwich bags, food containers.
2. Soak your filters
After you have soaked them under the faucet, lay each filter out on a plate.
3. Fold Your Seeds
Place the seeds on the wet filter, then fold the filter over them so they stay inside.
4. Bag your seeds
Place your folded filter inside a plastic sandwich bag and seal the bag shut.
5. Containerize your seeds
Place the sandwich bag inside of a food container and secure the lid.
6. Refrigerate your seeds
Put them in a safe place inside your refrigerator for about a month.
7. Plant your seeds
Remove your seeds from the refrigerator and plant them in a seed starting tray or a pot, or sow directly outdoors.
Cold Dry vs Cold Moist Stratification Results
100% of the Cold Dry Stratified and 92% of the Cold Moist Stratified (1 seed didn’t sprout) have germinated. All the Cold Moist Stratified seeds sprouted first, starting after just two days. The cold dry seedlings were a few days behind, but all plants from both treatments look healthy and continue to grow.
Cold moist stratification worked well using a wet coffee filter sealed inside a plastic baggie. The filter/seeds were still wet a month later and none of the seeds sprouted prematurely inside the refrigerator.
I only tried cold moist stratification on purple and 75% of the seeds (3 didn’t sprout) have germinated. I have had a problem starting purple seeds using dry cold stratification in the past. I consider this a huge success.
Gomphocarpus fruticosus (swan milkweed)
I was curious to see how seeds from a warm weather variety would be affected by cold treatment. The germination rate was 0%, although I think seed quality was a contributing factor.
I was able to get 7 seeds to sprout earlier by soaking the seeds in warm water before planting. I will try experimenting with G. fruticosus next season, after I’ve harvested fresh seeds from our garden.
Asclepias tuberosa (butterfly weed)
Want to see something totally amazing? Community member Gwendolyn J. sent me this photo of Asclepias tuberosa seeds she started in a container of water! She was also able to do this successfully with tropical milkweed seeds.
Gwendolyn’s Steps to Milkweed Seed Germination in Water
1. The milkweed seeds were not cold stratified beforehand.
2. I used plain room temp, rain water, I guess about a cup in the containers, (plus a tablespoon from a gallon of rainwater mixed with 1 cup 3% Hydrogen peroxide). I spray it on seedlings and their soil to kill fungus gnat larvae.
3a. The containers are also under lights for 14 hours a day and room temp. is 70° F.
3b. If room temp is below 70° F use a heated seed mat under the containers
4. The milkweed seeds began to germinate within a few days.
5. I pour them out on soil when I start seeing roots, then sprinkle a little soil over them.
Gwendolyn, on behalf of our community, I would like to thank you for sharing this surprisingly simple way of starting milkweed seeds!