Without prolonged exposure to cold temperatures, your milkweed seed is unlikely to sprout.
What does that mean? In the wild, milkweed plants scatter their seeds quite late in the season, at a time when the coming cold would kill any seedlings that germinated right away. However, the seeds of milkweeds (and other late-season flower plants) are cleverly programmed to delay germination until after they’ve been exposed to winter’s cold, followed by gradually rising temperatures in springtime. This adaptation is known as stratification. Cold stratification helps to break the seeds’ natural dormancy cycle. Exposure to winter temperatures help soften or crack the seeds’ hard outer casings.
Milkweed seeds require cold stratification.
Getting Started: Understanding Milkweed Seed & Germination
In warm zones without winter frost, or if you are starting your seeds in spring, you can cold-stratify seeds in your refridgerator!
Follow our instructions for starting milkweed from seed, including Common Milkweed (Asclepias syriaca), Swamp Milkweed (Asclepias incarnata), and Whorled Milkweed (Asclepias verticillata). We have found these techniques best for good growing results.
In most areas, when you plant seeds outside in fall, seeds can go through the cold stratification process naturally. If you are planting seed outside, we suggest seeding in late fall so that Milkweed seeds can 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 is warm in the spring, the seeds will germinate on their own.
Why plant milkweed? Milkweed are the host plant for Monarch Butterflies: the leaves of milkweed plants are the sole food for monarch caterpillars, and the nectar-rich plants are an essenital food source for adult butterflies. The Monarch Butterfly population has declined a whopping 90% over the past decade due to the loss of meadows and habitat (especially in the Midwest). Plant milkweed in your gardens to help support these amazing North American butterflies!
Situate this perennial in borders and wildflower gardens to enjoy its colorful floral display and to attract bees and butterflies to the garden. The plant grows 3 feet tall by 12 inches wide and boasts flat, 1-2 inch diameter clusters of orange, orange-red, or yellow flowers. These fragrant flowers appear in July and August. The stems ooze a milky sap when broken. Slender, hairy, 4-5 inch long leaves line the stem
About Asclepias tuberosa:
Pronunciation: a-skle’pe-us tu-ber-o’så
Origination: Asclepiadaceae; native to the United States and Canada
Common Name: Butterfly Weed
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.
Planting In Fall: If you’re planting Milkweed seed in the fall, let nature do the cold stratification for you! There is no need to place your seeds in the refrigerator before planting, you can plant seeds directly into the soil after there have been a few frosts in your area. This allows for the seeds to remain dormant for the winter and come up in the early spring. Clear away any existing growth and using your index finger to measure, create 1.5″ holes for each Milkweed seed. We recommend spacing seeds about 4-6” apart. Place a seed in each hole and cover. Water thoroughly.
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.
Transplanting Milkweed (Asclepias) Seedling Outdoors
Planting In Spring: Once the 30 days are complete, it’s time to plant the cold stratified Milkweed (asclepias) seeds. We recommend planting in 2-4” peat pots. Fill peat pots ¾ of the way with 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.
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. In our experiment, this happened to us. 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!
Where to Plant: 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, but 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.
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.