Germinating Milkweed seed varieties: a home gardener’s perspective

Having been bitten by the “grow it” bug many, many years ago, I consider myself pretty adept at nurturing seeds. Over the years I’ve developed my own way of germinating that’s been highly successful whether the seed is annual flowers or heirloom tomatoes (and lots of others in between).

But then along came milkweed.

Once we started the Dunbar Memorial Garden my focus did a hefty 180 with my efforts almost completely focused on native plants including those of the Asclepias variety. Back in 2007 we planted several stands of native milkweed from Swamp (incarnata) to Whorled (verticillata) to Butterfly (tuberosa) and I knew absolutely nothing about any of them except that they would help the Monarch butterfly population. Back then I was still shrouded in a haze of shock, surrounded by myriad of volunteers, focused on every little distraction and certainly incapable of remembering most of the gardening knowledge I had gained during my life. So, in hindsight, it should have come as no great surprise when after 3 or 4 years we all of a sudden realized our garden no longer had any milkweed except the tuberosa. And thus my obsession with it began.

After much research and time spent dissecting information available on the internet (oh boy there’s a lot, and a lot of it unfounded and misguided), I drew a few conclusions: 1) if you want to keep milkweed in your garden, keep planting it 2) if you use a lot of volunteers in your garden including young folks who don’t know the difference between a dandelion and a newly emerging Swamp Milkweed, expect losses in your population 3) growing milkweed from seed requires some patience and timing and 4) repeat item #1 bearing in mind that most milkweed varieties only live from 4 to 6 years with the possible exception of Tuberosa and Syriaca – the latter can be pretty aggressive and does best with lots of space to do so.

I think it’s a gardener’s habit to never be completely satisfied, to always be plotting and planning what to do “next year” or “this fall” – move such and such in front of so and so, oh how lovely this would look paired with that and etc etc etc. But the funny thing is, at least at the Memorial Garden and with the exception of a few random placements that totally worked, the best groupings of our native plants, our native plants basically did on their own. A lovely false blue indigo appeared beneath the tall branches of the bur oak. Next to that a wild bergamot took root. Then “magically” an ironweed sprouted and together they look better than anything I would have planted together. But I digress, back to milkweed.

When we replaced our “missing” milkweed we purchased plants but I wanted to learn to grow it from seed and then to grow different varieties. That fall mature swamp milkweed seed was raked into the soil then lightly covered with soil, we pressed it in by walking over it then watered it and let it go. The next spring we had about 60 new milkweed plants – I hadn’t bothered counting the seeds probably because I was leery of how well they’d do – but I expect I planted over 100.  If you ever want to get really frustrated, google “germination rate of milkweed seed.”

The next fall I planted “pots” into the ground then filled them with soil and added mature milkweed seed from both the garden and seed purchased online. I sowed swamp, white swamp, showy, green and common. Each pot had a different variety. Because I have (damned) squirrels in my backyard I covered the row of pots with a length of lightweight Agribon shade cloth. In the spring, several swamp milkweeds emerged as well as a nice amount of the white swamp but nothing from the other varieties. I was dismayed which led to more research and so this spring I’ve been experimenting and experimenting some more.

I won’t go into too much detail on all the methods I tried but I will share a brief synopsis of each.

  1. Various seed cold stratified (30 days) then planted in pots of vermiculite with bottom heat (a lamp) and overhead light (shop lights). I had varying success with this method. Annual Tropical (curassavica) milkweed did quite well with a 75 to 80% germination rate.  White Swamp (incarnata) also performed well with about 60% germination. Results for other varieties including Showy, Prairie and Common were very low. Only a few sprouted.
  2. Various seed cold stratified (30 days) then planted into raised beds in a hobby greenhouse. Seeds were planted about 1/2″ deep. Results were absolutely awful, only about 6 plants out of about 60 seeds germinated. On a side note, we had extremes in weather that month with heat, cool, rain and hot sun. I did not attempt to control the temps in the greenhouse with the exception of opening/closing doors and windows.
  3. Various seed cold stratified (except Tropical) placed in small clear plastic containers of water with sealed lids, placed under shop lights with bottom heat (lamp). Tropical milkweed germinated at 100%!!! White Swamp germinated at 40%, nothing else germinated.
  4. Various seed cold MOIST stratified (placed in baggies with damp vermiculite) for 30 days then sown into small pots of damp vermiculite and placed on top of the refrigerator (for bottom heat). For this experiment I used Spider (viridis), Tall Green (hirtella) and Poke (exaltata) milkweed seed from Prairie Moon Nursery. Within a matter of days (!!!) seeds began germinating and after 1 week they are all about 50% germinated. Because the top of my fridge is dark (it’s under a cabinet), today I moved the seedlings under lights and added bottom heat (lamp).

So far my favorite method (at least for starting milkweed indoors) is number 4. I plan to wait a week or so then pot up the seedlings and later this month move them outdoors. Since it is so late in the season (and Kentucky is damn hot in July and August) I may keep them potted and protected growing outdoors until Fall when I’ll move them into the ground. Updates on this method will be forthcoming.

Milkweed seed was mixed with damp vermiculite in a resealable baggie then refrigerated for 30 days
After about 1 week, seeds were moved from the top of the fridge to a grow area under shop lights with a lamp for bottom heat


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