How and When to Harvest Milkweed Seeds

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Milkweed is the sole food source for monarch butterfly caterpillars. Monarchs have greatly decreased in population over the years, primarily because of habitat loss. As fields and meadows have given way to parking lots and shopping centers, the places where milkweed grew naturally have started to disappear. Luckily, we as gardeners can play an important role in ensuring that monarchs have plenty of milkweed.

Here in Michigan, there are six types of native milkweed, all of which provide food for monarch caterpillars:

  • swamp milkweed (Asclepias incarnata)
  • butterfly weed (Asclepias tuberosa)
  • common milkweed (Asclepias syriaca)
  • whorled milkweed (Asclepias verticillata)
  • tall milkweed (Asclepias exaltata)
  • prairie milkweed (Asclepias sullivantii)

Most of these milkweeds are native throughout the state, with the exception of swamp and prairie milkweeds, which are native only to the southern part of the lower peninsula.

Finding Milkweed to Harvest

Milkweed grows naturally in meadows, fields, and ditches throughout the state. You can identify milkweed in three ways: via its flower, its foliage, and its seed pods. The blossoms range in color from light pink to purple, except in the case of butterfly weed, which has bright orange flowers. The foliage is shiny, alternating up and down the stem, with long, feather-shaped leaves. Depending on which variety of milkweed it is, these leaves may be large or fairly narrow. In any case, when the leaf is snapped, a white sap should be visible; this is what gives “milkweed” its name. Be careful, though — this sap is a skin irritant, and you definitely don’t want to rub it in your eyes!

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As far as the seed pods, they usually start appearing here in Michigan in late summer. At first they are bright green and quite plump. They look like a weird, kind of spiny/bumpy fruit. As the season progresses, they’ll get a bit lighter in color, eventually turning a greenish-yellow. When they’re at this stage, they may start splitting, and that is when you know the seeds are ready to harvest. When you open the pod, the seeds should be dark brown. If they’re green or light brown, they’re not mature yet and won’t sprout when you plant them. I always look for signs of pods splitting, which is nature’s way of telling you that the seeds are ready. You might lose a few seeds this way as they’re blown away by the breeze, but believe me, there are plenty more inside the pod.

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Please note that you should always ask permission before harvesting seeds from private land, and of course seeds should never be removed from state parks or national forests.

How to Harvest and Separate Milkweed Seeds

To harvest the seeds, simply pull the entire seed pod off of the plant. You can actually store it as is in a paper bag until you’re ready to plant, or you can go ahead and clean the seed now to make it easier to store (in a cool place – preferably a refrigerator, which keeps the seed at a constant cool temperature. Milkweed needs a period of cold stratification to germinate; the refrigerator storage will provide that.)

The trickiest part of the entire process of saving milkweed seeds is separating the dark brown seeds from all of the white fluff attached to them. This fluff is essential to the milkweed’s survival. It acts as almost a parachute, and when the wind blows, it carries the milkweed seeds further away because of that fluff attached to it, dispersing the seed over a wider area. But for seed collectors, it can be a bit of a pain.

Here’s how I do it.

Sometimes, especially if you’re just harvesting one pod and it’s begun to split but hasn’t completely exploded yet, you can simply pull the wad of fluff and seeds out, run your fingers down it, and easily separate the seeds that way. The seeds fall into a container or tabletop, and the wad of fluff stays in your hand. That’s what I was able to do for these pods. You can see how they’re all still pretty self-contained below.

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If you have more than just a pod or two, or you just don’t want to risk making a mess (that fluff goes EVERYWHERE…) try this: open your seed pods and empty them, fluff and all, into a paper bag, small coffee can with a lid, or a jar. Close the container and give the whole thing a good, vigorous shake. You can even add a penny or two to the bag to help agitate the contents even more. What the shaking does is shake the seeds loose from the fluff. The heavier seeds will fall to the bottom of the bag or jar, leaving the lighter fluff at the top. So after a few good shakes, all you have to do is open your container, lift out the ball of fluff that is on top, and in the bottom, you’ll see your cleaned seeds.

(If you have a huge amount of seed to process, check out this contraption from Monarch Watch: a seed separating machine for milkweed.)

Storing Milkweed Seeds

As I mentioned above, it’s best to store milkweed seeds in a cool place, any my preference is the refrigerator. I like to store my seeds in paper envelopes, which are easy to label, or in jars if I have a lot of seed.

What To Do With Extra Seeds

Often, you only really need a seed or two, especially if you have a small garden, while a milkweed pod can yield dozens of seeds. If you find yourself with more seeds than you can use, here are a few ideas:

  • Offer them to gardening friends
  • Contact your local 4-H, garden clubs, or wildlife restoration nonprofits to see if they would like to take some off your hands
  • If you’re involved in any online gardening groups or forums, offer them as part of a seed trade or for a SASE for those who want some.
  • Store them in your fridge or freezer. They’ll keep, stored this way, for a very long time. If you decide you have room for more milkweed plants, you’ll already have cleaned seed on hand.

I hope this has been helpful. There is nothing quite like sitting out in your yard or garden and watching monarch butterflies fluttering around the milkweed you lovingly planted for them. These beautiful creatures need all the help we can give them, and, in exchange, we get flowers plus the joy of seeing them in our garden.