Milkweed seeds require cold stratification.
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.
Cold stratification is very important for the germination and growth of Milkweed.
Without prolonged exposure to cold temperatures, your milkweed seed is unlikely to sprout.
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.
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 step by step guide: How To Cold-Stratify Seeds For Spring Planting
At-Home Cold Straification Summary: 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). Label your seeds, and be sure to choose a low-traffic place inside your fridge where they won’t get damaged.