Starting Seeds Indoors Part 2-
Performance Enhancing Secret

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.

If you’re anxious to get this season growing, try a performance enhancing trick that works like a charm for getting annual (tender perennial) milkweed varieties off to a fast start.

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:

2015 Update

  • I tried using the milk jugs that I used for winter sowing last season. This didn’t work very well because the heated seedling mat couldn’t effectively warm the soil
  • This season I’m using the small plastic cups again. Traditional 16 oz cups would also work
  • I’ll still be using the performance enhancing trick listed below for faster germination
  • After the seeds germinate, the seedlings will be placed under t5 grow lights


My current seed starting system includes old seed starting trays, clear tray covers,  5 oz. translucent cups, shelving for the trays, T5 grow lights, and a heated seedling mat.

Starting Milkweed Seeds Indoors can be done using convenient household items like these plastic cups.
3 Holes 1 Cup

As I write this, my heated seedling mat is keeping my Gomphocarpus fruticosus (swan plant), Calotropis gigantea (giant milkweed), and Asclepias curassavica (tropical milkweed) seeds a balmy 75-80° F while it’s below zero in the butterfly garden.

Why does this matter?

Since the seeds germinate at around 75° F, northern germination outside might not occur until late June or July. So your milkweed gets off to a super slow start and then, before you know it…your “runt of a plant” gets rudely interrupted by winter’s return.

I’d heard of heated seedling mats before, but foolishly discounted them as 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 might be easier, what’s the point if these are the measly results:

Starting seeds indoors each winter is a great way to get a huge head start when growing warm weather milkweed varieties. Try this performance enhancing trick so your late season milkweed plants don't look like this!
Teeny Tiny Tropical…Late August!

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, 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 or winter.

In my next post on starting seeds indoors, you’ll see photos of my entire setup and, whether or not seed starting indoors was successful.

Click Here for Milkweed Seed Starting Results (update by 2-28-2015)

Do you know other gardeners in USDA Zone 8 (and below) interested in growing annual milkweed plants for monarchs? Share this page and help a gardener out:

Print Friendly


  1. Andrew Kliss says

    I agree that heating mats are one of the best ways to germinate seeds and coax roots from cuttings. Naturally, I use them on my tropical seeds, and use a mat on my native milkweeds also after stratifying them in the reefer for six weeks.

    Even here in sunny SoCal a mat gets things going MUCH sooner than relying on spring to arrive. I start my seeds in December. by March they go outside six to eight inches tall on some species!

  2. Helen says

    Hi Tony ,

    I had just bought tropical milkweed plant from eBay five min.
    Ago and realized that I don’t know what to do with a dormant plant.
    Anysuggestions would be appreciated. I bought the plant because I don’t have any luck germating seeds. I’ve tried in the past and just ended frustrated.


    • says

      Hi Helen,I’m assuming you want them to come out of dormancy now? You could put them near a window or even put grow lights or CFL lights on them so they break dormancy. If you want them to stay dormant you could always stick them in a cool basement or garage. If you don’t want dormant plants, you could also try canceling your order. Hope this helps, Tony

  3. Helen says

    Hi Tony,
    I just heard from the seller he’s going to ship the plant at a later date
    We had over 42″ of snow and he didn’t want to risk something happening to the plant so I guess I’ll have to wait….

    I decided to give the seeds a second try so I bought some fome a past seller that I’ve used in the past how much hydrogen peroxide should I use on the seeds to help quicken the pace?

  4. Brian says

    Hi Tony,

    We want to start growing some tropical and balloon milkweed seeds inside, but I’m a little confused on the timing of when to start the seeds. From the dates on your post, it looks like you are starting your annual milkweeds in February.

    Here in Michigan, the date that everyone throws around for planting annuals is typically Memorial Day, maybe a little earlier if the weather is nice. If I was to start my seeds in February, I would be afraid that my balloon plants would be three to four feet tall before I even planted them outside?

    Am I reading the post correctly? Have you started growing your 2015 annual milkweed plants already? Do you move your plants outside in early May if the weather is nice? Thanks for any advice on when to start annual milkweeds from seed.

  5. says

    Hi Brian, 2 months before planting should give you all the head start you need. I started seeds early this season because I unsure of seed viability.

    I’m also trying some experiments so I can help you and the community start milkweed seeds with the highest germination rate possible.

    It really doesn’t matter how big your balloon plants are, if you have the room to let them get that large. The one concern would be if they had weak stems and started leaning over. An oscillating fan really helps with that though. I’ll be reporting more on seed-starting the next couple weeks…

  6. Danielle Moraine says

    Hi Tony,
    I have a ton of tropical milkweed seeds to plant, I’m hoping for a good turnout! I live in South Florida, as you can imagine the weather is already very warm (80s). Do you think I could grow my seedlings on the back lanai? Or am I better off growing them inside?
    Thank you!

    • says

      yes Danielle, start them outside. I start seeds to extend our Minnesota growing season. You don’t need to do that in Florida. Good luck with your seeds!

Leave a Reply

Your email address will not be published. Required fields are marked *