Starting Milkweed Seeds Inside for a
Longer Growing Season
Starting seeds indoors requires more patience if you’re letting things progress on nature’s terms…but there’s a quicker path to butterfly garden success.
But first, if you’re completely lost, you probably missed the first post from this seed starting trilogy. Once you’re up to speed, continue reading below…
My current seed starting system includes seed starting trays, clear tray domes, 5 oz. cups, seed starting soil, a heated seedling mat, shelving for the trays, and T5 grow lights.
Plant your Milkweed Seeds
- I prefer using 5 oz. translucent cups (as opposed to planting in seed tray inserts) so I don’t have to transplant before spring planting. The inserts are fine if you prefer them.
- Make 3 drainage holes in the bottom of each cup
- Fill the cups with seed starter soil inside of the tray
- Water each cup so the soil is saturated
- Place 2 seeds in each cup (space them so they both have room to grow)
- Cover them with more soil
- Spray the soil with a water bottle
- Place the dome lid over the tray
- Slide the the tray on to your heated seedling mat
- Remove the heated seed mat after your seeds have sprouted
- Place the seedlings under t5 grow lights OR
- Place them by a sunny window- we place some in our 3-season porch with the dome lid on to retain more moisture and so the seedlings won’t freeze.
Growing 💡: While your seedlings are indoors, an oscillating fan can be used to mimic an outdoor breeze to promote stronger, straighter stems.
Alternative Plant your Milkweed Seeds
If you use the seed starter trays, you could transplant the seedlings into a new winter sowing container. In Minnesota, I’ve kept ours in the 3-season porch (with lid secured!) until about St. Patty’s Day, then moved containers outside. On nights well-below freezing, they’re moved into the garage or house.
Once the threat of frost is over, remove the lid and let the seedlings grow until it’s time to transplant.
Why does heat matter?
Since the seeds germinate at around 75° F, northern germination outdoors might not occur until late June or July. This gets your annual milkweed plants off to a super slow start and then, before you know it, their fate is sealed by a Game of Thrones…Winter is Coming.
I foolishly believed that heated seedling mats were a “marketing ploy” in my early days of gardening. Once I broke down and bought one, I was simply amazed by the results. Not only did my seedlings sprout in record time, I also had my highest germination rate ever for tropical milkweed.
While spring sowing tropical seeds outside might be easier, what’s the point if these are the measly results:
This late-August tropical milkweed plant started from seed in a local butterfly garden. Even with the encouragement of soaking rains and sizzling summer sun, it never grew up to share nectar with a monarch, or feed hungry caterpillars.
For annual milkweed, starting seeds indoors can mean the difference between a long summer of beautiful blooms with butterflies, or the joyless alternative above. I know what I’m choosing…
Note: While starting seeds indoors is a fantastic option for starting your annual milkweed supply, it’s much easier to continue that supply by taking yearly milkweed cuttings in fall, winter, or early spring.
In my next post, I’ll discuss how to proceed once your milkweed seeds have sprouted.
In case you’re wondering about any of the supplies we use, here’s the seed starting supply list