How to Germinate and Grow Milkweed Seed
Instructions for preparing and planting Common Milkweed Seed (Asclepias Syriaca) and Swamp Milkweed (Asclepias Incarnata) from seed.
Let’s Get Started: Understanding Milkweed Seed & Germinating
Step 1: To start Milkweed seed we recommend starting inside, but before this happens Milkweed seeds need to go through a cold stratification period. Cold stratification is very important for the germination and growth of Milkweed. It helps break the seeds natural dormancy cycle. To do this, we recommend placing Milkweed seed in a damp paper towel or damp sand in a zip lock bag and place in your fridge for 3 – 6 weeks (30 days). Place in an area of the fridge, where it won’t get damaged. We taped ours to the bottom of a refrigerator shelf.
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 peat pots ¾ of the way with 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 ¼ inch of soil on top of the seed.
Watering - Gently water the planted seed to give additional hydration. The best way to water is from the bottom up. Use a flat pan under the peat pots and add a half inch of water to the bottom of the tray. Don’t over water 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; if it’s wet, wait for the soil to dry out to water.
Light Requirements - For the next few weeks, make sure the 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 the light. Ideally a sturdier stem is better. Cold stratified seeds should germinate and sprout within 10-15 days once planted. In total Milkweed from the day they are cold stratified to growth can take 40 plus days, so be patient!
Other 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. Milkweed seed will have a long winter of dormancy, so once the sun comes out and the ground warms in the spring, the seeds will germinate on their own.
Transplanting Milkweed Seedling Outdoors
Step 3: Milkweed does well in open areas with full sunlight exposure areas like fields, parks, cultivated gardens, roadsides, highway medians, and road sides. We suggest transplanting Milkweed when the plant is no larger than 3 inches tall. In most cases in transplanting, the Milkweed plant will go though some shock and could lose all its leaves. This happens, don’t panic. The plant is trying to establish its roots and will eventually grow leaves again. This is the main reason we suggest planting seeds in peat pots, because Milkweed roots are very sensitive. Peat pots breakdown over time in the ground, which allows the milkweed roots to grows without being disrupted. We found this to be the best way to transplant. If you decide to plant in plastic containers, make sure it’s deep enough for roots to grow. If you receive a plant already grown in plastic, be careful to take out the plant and not disturb the roots.
When to Plant Milkweed
Soil moisture and temperature are very important when growing Milkweed. The best time to plant Milkweed is in early spring after the danger of frost has passed. If you plant seeds late in the spring, the seeds may not grow due to germination time and temperature. 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, but 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. So minimizing the time growing in a pot and transplanting them as young plants is the best approach