Instructions for preparing and planting Common Milkweed (Asclepias syriaca), Swamp Milkweed (Asclepias incarnata), and Whorled Milkweed (Asclepias verticillata) seeds. We have found these techniques best for good growing results.
Let’s Get Started: Understanding Milkweed Seed & Germinating
Step 1: To start - Milkweed seeds, we recommend starting indoors, but before this happens Milkweed seeds need to go through a period of cold stratification.
Cold stratification is very important for the germination and growth of Milkweed. It helps to break the seeds natural dormancy cycle by exposing the seed to winter-like temperatures that help soften or crack its hard outer casing. Without prolonged exposure to cold temperatures, your milkweed seed is unlikely to sprout.
To do this, put your Milkweed seed in a damp paper towel or some damp sand inside a zipper bag, and place in your fridge for 3 – 6 weeks (30 days). Choose a low-traffic place inside your fridge where it won’t get damaged. We taped ours to the bottom of a refrigerator shelf.
Growing Milkweed Indoors
Step 2: Planting - Once the 30 days are complete, it’s time to plant the cold stratified Milkweed seeds. We recommend planting in 2-4” peat pots. Fill the peat pots ¾ of the way with a 'seed-starting potting soil' and gently add water. Water should be able to drain through the peat pots. Once the soil is damp, place 1-2 cold stratified seeds into each pot. To finish, place 1/4 inch of soil on top of the seed.
Step 3: Watering - Gently water the planted seed to give additional hydration. The best way to water is from the bottom up: sse a flat pan under the peat pots and add a half inch of water to the bottom of the tray.
Don’t overwater, as it can cause fungus. Water every day, or every other day as needed. The best way to test the soil dampness is to touch it; if the soil seems dry then add water, but if it’s wet, wait for the soil to dry out before adding more water.
Caring for Milkweed Seedlings After Planting
Light Requirements - For the next few weeks, make sure your Milkweed is either in a sunny window, in a green house, or under a grow light. Milkweed needs lots of sun and warmth to grow.
If you’re using a grow light, make sure to lower the bulb closer to the pots, or your seedlings may become leggy as they stretch to find the light. You can see that in our experiment (below), this is exactly what happened!
Ideally, a sturdier stem is better. Some people have good luck pointing a gently circulating fan towards their growing seedlings, in an effort to strengthen young plants.
Cold-stratified Milkweed seeds should germinate and sprout within 10-15 days once planted. Remember, from stratification time in the fridge to first sprouts can take 40+ days, so be patient!
Other Milkweed planting options: Place dry seed (not stratified) in seed-starting soil and plant in peat pots under a grow light or in a greenhouse to germinate seeds. The success rate for this is low and more difficult to accomplish. If you choose to use this option, it can take months for the seeds to germinate.
If you are planting seed outside, we suggest seeding in late fall, and let the Milkweed seed lay on the ground through winter. This will give your Milkweed seed a long winter of dormancy. Once the sun comes out and the ground warms in the spring, the seeds will germinate on their own, usually at the perfect time!
Transplanting Milkweed Seedlings Outdoors
Step 4: Transplanting - Milkweed does well in open areas with full sunlight exposure. Remember: fields, parks, cultivated gardens, roadsides, highway medians, and road sides are all favorite places for spotting native Milkweeds.
We suggest transplanting Milkweed when the plant is no larger than 3 inches tall, as many varieties produce a long taproot that cannot be disturbed. In most cases, the transplanted Milkweed plant will go though some shock and could lose all of its leaves. This happens, so don’t panic! The plant is trying to establish its roots and will eventually grow leaves again.
Transplant shock is the main reason that we suggest planting seeds in peat pots, as Milkweed roots are very sensitive. Because Peat Pots break down over time in the ground, the milkweed roots are able to grow through without being disrupted.
While we've found this to be the best way to transplant milkweed, sometime peat pots are not available. If you do decide to plant in plastic containers, just be sure that they're deep enough for long roots to grow. If you receive a plant already grown in plastic, be mindful when taking the plant our of the pot, so as not to disturb the roots.
When to Plant Milkweed
Soil moisture and temperature are very important when growing Milkweed. The best time to put in Milkweed plants is in early spring after the danger of frost has passed, while the best time to plant milkweed from seed is in late fall - this allows mother Nature to take care of the cold stratification for you!
If you plant milkweed seeds late in the spring, the seeds may not sprout as theyo won't be exposed to a duration of cold temperatures. Common Milkweed seed doesn’t germinate over 85 degrees.
Caring for Milkweed Plants
Once your seedling is planted, water it for a few days to get it established. After that, the plant doesn’t need a lot of supplemental water. Only water if you have an unusual dry spell.
Peat pots are nice to use, but you need to be sure there is no top edge above the soil line after transplanting. In dry climates, this will wick away valuable soil moisture. A small 2 1/2" diameter x 3 in. deep pot is ideal.
Asclepias are somewhat finicky native plants. Minimizing the time they spend growing in a pot and transplanting them as young plants is the best approach.
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