How to grow milkweed from seed
Gathering Milkweed Seeds
Milkweed seeds in their pod
To easily collect the milkweed seeds—i.e. getting the seeds without the fluff—we collect the pod when the pod has split, and it has just begun to open rather than waiting for the seeds' little “parachutes“ to start floating all over.
Wait until you see the pod starts to show the split, though. If you open the pod before it's ready, the seeds won't be ripe.
Then, we just hold the end and strip off the seeds. We're left with the not-yet-fluffy fluff in one hand, and the seeds in the other.
If we don't get to them before they're beginning to get fluffy, we just enjoy the fluff and collect the seeds anyway. It's just a little more of a challenge to separate the seeds from the fluff.
If you're not going to be sowing the seeds right away, store them in a paper envelope or bag, not plastic.
Growing Milkweed from Seed Outside
The easiest way is to sprinkle some seeds around in the fall after a killing frost and wait for spring. The seeds experience winter and know when it's time to get growing in spring.
Nature plants seeds whenever they ripen and drop from the plant, and plants can grow this way, but the little plants that germinate will face a killing frost. If you wait to sow the seeds after a killing frost, the seeds will be ready to grow early in the spring. And seeds often germinate better in cool soil.
This is probably the easiest method, but it's hard to remember to look for them in the spring and to recognize the seedlings as they emerge.
Of course, we do get a few seedlings popping up on their own around the school, the seeds having been scattered by the wind the previous fall. Unlike some plants swamp milkweed seedlings aren't a problem since there never seems to be very many. If they do pop up where we don't want them, we just pull them out, transplant them elsewhere, or pot them up to give away. The more people growing milkweeds the better!
Growing Milkweeds Indoors
If you want to have larger plants for the beginning of the growing season, you'll need to start some plants inside.
If we grow them inside, we've found that cold stratification is really important if we want to get good germination and growth. The purpose is to trick the seeds into thinking they've been through winter.
It's easy to fool the seeds. Just put them in a moist paper towel, then into a plastic bag and leave them in the refrigerator for 3-6 weeks. Check on them occasionally; they may start germinating sooner, and you'll want to plant them then.
Here's the results of our Asclepias incarnata(swamp milkweed) experiment. Guess which is the flat whose seeds were cold stratified.
In the flat on the left: We soaked half the seeds, and we simply planted half with no special treatment other than being on the cold window sill all winter.
In the flat on the right: We cold-stratified the seeds. Virtually every seed came up, and much sooner than the seeds that were simply planted or soaked.
For a faster start, we start them indoors 6 weeks before the last frost date, growing them under fluorescent lights. This means that we put the seeds in the refrigerator as early as mid-November, so we can plant the seeds in late January. They'll start germinating about two weeks after planting.
We cover the seeds with about ¼" of soil or less. They need light to germinate.
Sometimes we even start some later in the season. Milkweeds are perennials, so getting off to a slower start the first year isn't a problem since we're just getting a head start for the following year. And milkweeds grow pretty quickly anyway.
