Starting Milkweed Seeds Indoors Part 2

How to Germinate Milkweed Seeds…Faster!

Start Milkweed Seeds Indoors for a huge head start on the growing season and returning monarch butterflies. Add heat for even faster germination within the first week...

Starting milkweed 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 milkweed 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 full spectrum grow lights.

Starting Milkweed Seeds Indoors can be done using convenient household items like these plastic cups.
2-3 Holes 1 Cup

Plant your Milkweed Seeds

  • I prefer using 5 oz. translucent cupsir?t=monabuttgard 20&l=ur2&o=1 starting milkweed seeds indoors (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 soilir?t=monabuttgard 20&l=ur2&o=1 starting milkweed seeds indoors 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 LED 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 heat mat 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:

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 bloomed to share nectar with pollinators, grew ample leaves to feed hungry caterpillars, and we couldn’t harvest seeds to support future monarchs.

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, you can yield even better results by taking 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

Click Here for Milkweed Seed Starting Results

Milkweed Plants for Sale and Seeds

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…
Share the Joy of Butterflies

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  1. I recently started purple and green/spider milkweed inside under lights. A complete newbie, I didn’t realize I should take them off the heat mat after sprouting. All the plants are healthy with great colour and working on their 3rd or 4th set of leaves. However they are very tall; strong, and unaffected by the fan, but a ton of spacing between leaf pairs. They are in 3″ peat pots, and I was planning on potting up to a 5″. Can I bury the stem a bit (or a lot) in the same vein as a tomato, Or am I out of luck? Pinch off the tops and hope for the best?

    Thanks in advance!

    1. Hi Christine, if you have several sets of leaves you could try pinching off the top set…hopefully you can get them planted outside in the next couple weeks before they start toppling over. The fan should help with this too.

  2. I’m wintering in Louisiana and had started some milkweed seeds. The seedlings are about 6 in tall and are out in the yard. Yesterday 3 lovely ladies fluttered around the plants and I have eggs!!!!! March 11, 2019. Now I have to go find some more plants since my measley little tray of plants will in no way be enough to feed about 10 (I hope) growing cats! We are directly in the path of the migration so I expect to see many more monarchs soon.

      1. So far I have harvested 260 eggs and 22 cats and have sent them to a butterfly refuge here in Louisiana where they have plenty of milkweed!! It’s very exciting and I’m planting more mw for next year as well as lots of nectar flowers! 🙂 Back to Iowa soon where I suppose I’ll be finding eggs on my plants there in a month or 2!

  3. Hello all! I am getting excited about the upcoming butterfly season here in Michigan, seeing how last year I had more “firsts” than ever before for new species in my gardens. I really attribute the increased diversity of butterflies directly to the increased diversity of native plants I’ve been adding the last two seasons. Plant it, and they will come!
    As for annual milkweeds, this year I am over wintering four potted tropical milkweeds that I grew from stem clippings and seeds last winter. I do not have room inside the house and we have a curious kitty that would probably nibble the plants if they were indoors. So what I came up with is a portable “incubator/grow tub” that I’ve kept in my attached, insulated garage. I took an old plastic tote tub and lined the inside with tin foil. Put a heat mat down inside of it and a few ceramic tiles under the tub to retain the heat. I then cut two 8″ holes in the lid for two grow lights which are on timers. So far the plants have survived the harshiest part of our Michigan winter, and are actually thriving so far! Even on the coldest of days, it didn’t drop below 50d inside the tub!
    I’ve added two more smaller tub setups like this for starting my annual seeds in and experimenting with trying to grow some cuttings of spicebush, wafer Ash tree, and wild black cherry trees!
    Hope everyone has a great season !
    Matt in the mitten

  4. Just wanted to mention that I picked up some of those really inexpensive white mesh grow bags that the roots are supposed to grow through without having to cut into the bags (like you have to do with peat pots), and one package comes with small, medium, and large sizes. The smallest size fits four to a 5×5 microgreens seedling tray (that fit 8 to a 1020 tray, for a total of 32 starts), and I can put an empty 5×5 tray upside down on top and tape/label it with freezer tape for cold stratification in the refrigerator. Those trays fit perfectly in the wider refrigerator door shelves. The smallest bags hold plenty of seed starting mix so I should not have to do any transplanting at all. A small mesh bag can be plopped into a larger mesh bag with potting soil or into a larger container if needed. What I really like about these bags is that there is give to them, so you make them fit into lots of differently sized containers. I don’t think they’re going to tear during the time they are used.

  5. I am not able to find any information on starting purple milkweed seeds. I bought some from China on ebay. Do you know if I have to cold stratify purple milkweed?

    1. Hi Lisa, ebay is a great resource for seeds, but I would stick to sellers from the US. Hopefully you got actual Asclepias purpurascens seeds. There are other buying options on this page if you need some in the future:

      Purple Milkweed Page

      Yes, purple milkweed typically has a higher germination rate with cold treatment:

      Cold Moist Stratification

  6. I am confused about starting tropical milkweed from seeds in zone 7b. I just received some seeds from my neighbor. Can I just soak them overnight and plant them outdoors (it has hit 100 here the past few days), or do I need to start them inside? It said sun or partial shade–what is the best. I have never done this before, and I would like to do a good job.

    1. Hi Cindy, summer isn’t the best time to start seeds, but you can try directly outdoors (after soaking)…spring is typically much better for establishing seedlings with moderate temps/more rain, depending on your region.

  7. You mention several times throughout your posts to use an oscillating fan, which makes sense. How many hours per day and what speed do you use? Thanks for all of your wonderful information. I am really enjoying your blog.

    1. Hi Karen, for at least a few hours a day up to about 6. Personally, I prefer to get seedlings out in the 3-season porch where they can get a natural breeze before going outside permanently…good luck with your seedlings!

  8. I live in Northern Ohio. I started my common and tropical milkweed a couple weeks ago. I don’t use a heating mat, but I place the racks of plants in front of my soyth-facing sliding doors. The sun radiates through and keeps things nice and warm … I actually have to monitor yo make sure they don’t get too jot at times!
    This year I had germination in 4 days!
    Seedlings are now between 3 and 4 inches tall with true leaves.
    So excited for the season!!

  9. Just added a heated seedling mat with freshly planted Tropical milkweed seeds. I noticed that there is a lot of condensation on the clear cover. I didn’t have this problem before the heated seed mat. Should I poke vent holes in the cover or is it okay to for the extra moisture?

    1. Hi William, increased heat/moisture create the greenhouse effect that promotes faster germination.

  10. I am new to butterflying , but am hooked. I live in north western Wisconsin. I have seeds from our local milkweed but would like to try a couple of other kinds hearty to my area. What would you suggest?

  11. This year will be my first attempt at growing milkweed. I live at the edge of a marsh in south central Wisconsin. I hope to attract monarch butterflies. I have started outside about 25 jugs with various types of milkweed and others that need the cold process. I purchased several kinds of tropical milkweed seeds and am starting those indoors. I have 2 heating mats but that will not be enough for my needs. They can be a little pricey.

    In my basement I have radiant floors. They are not turned on and the air temp is about 65 degrees. Do you think I could put the plants on the floor and turn on the heat and that would make a giant heat mat? I have several grow lights hanging from the ceiling as I have some other plants overwintering there (they are starting to come out of hibernation).

    1. Hi Janis, I’m not sure how warm your radiant floors will get but if they stay under 80° it’s definitely worth a shot…good luck!

  12. Dear Mr. Gomez, forgive me for I have sinned. It’s because of ignorant people like me, the Monarch Butterfly isn’t population is not flourishing!
    Very, very long story short; I was given a plant without knowing what it was 2 years ago. This year the plant thrived but many orange aphids and caterpillars. In keeping the plant healthy I killed all the pesky aphids “AND CATERPILLARS” found on my plant daily.
    Yesterday I finally found the time to research what the plant is and learn the recommended pest control was, needless to say I was horrified to learn what a jewel I had and what a horrible crime I’ve been committing the past months.
    I’m more than anxious to start raising the Monarch’s next year, and as I discovered last night you are surely the expert.
    My question to you is: where should I start learning? You have hundreds of fascinating articles…can you recommend where to begin?

  13. This morning 3 Monarchs emerged here inside. The weather doesn’t permit me to release for another 4 days. (40 degrees). My milkweed won’t last long for the 20 cats that I’m raising .BUT!! I want you and others to know that I purchased 2 quarts of milkweed yesterday at Lowes. Today I found my cats turning black and not eating! Called my local nursery..THESE PLANTS are poisonous because the plants are raised with Pestacide. I lost 7 or 8 different sized cats that were 100 percent healthy. Just a warning!!! Buy good milkweedat Walmart!
    To change the subject, can I used a water soaked cotton ball for new Monarchs to drink while waiting for the temperature to warm up here in Tampa??? Please advise..I’m desperate and don’t want to lose them!!

  14. Another question…….I cannot find 5 oz. plastic cups at several places I’ve looked. Where did you find yours?

  15. I was wondering, when you plant tropical milkweed seeds indoors, do they need light to germinate? I’ve read that they do and that they don’t.

    1. Hi Pam, mine don’t get much light for germination…maybe a couple of hours of sunlight a day? After they germinate they are moved under grow lights.

      1. How many hours a day do you keep them under grow lights? Thanks!!

  16. My giant milkweed was up in 3 days. Did not use saltpeter this year. Tropicals coming up today, 5 days.
    The trick is to give them a warm bath overnight. I keep everything at 85 degrees or so. Most of the seeds had sprouted in 24 hours. Don’t be cheap, go to the garden center and pony up for a heat mat, cells and a dome. Will last for years. 20 bucks or so. Beats making your own and a lot faster. And you do not have to look like a hillbilly when your fellow gardeners come over to see your project.

  17. Hi all,
    Interesting to read about the problems you are experiencing regarding climate.Something I would like to add for those of you interested in establishing a “Butterfly Garden” is the notion of companion plants.
    For the past three or four years we have noticed Monarchs over-wintering in our garden here in New Zealand.Our winters are relatively mild by Northern Hemispheric standards-typically in the 30 to 60F range. We have around 100 or so butterflies flitting around the garden at the moment–either in a big eucalyptus tree or in the nearby Lacebark ( or in the Callistemon (Bottlebrush); both these trees have flowers that attract the butterflies and seem to sustain them over the winter months.
    As well as planting as many swan plants as possible(and keeping some guarded in reserve) I reccomend a longer term view of providing these ‘companion’ trees/plants in climes where suitable.The further south you are in USA eg the better chance you would have to keep the butterflies coming back!

    1. Hi Ged, thanks for your post. Keep in mind, the eastern monarch population in North America migrates to Mexico. If they stayed in the southern US there would be increased disease due to overused milkweed. In regions like south Florida and southern California where there are monarchs year-round I know there are eucalyptus trees (west coast) and bottlebrush is big in Florida. More gardeners across North America are planting swan milkweed and we even have some growing in our northern garden. I agree having a wide variety of milkweed keeps the monarchs coming back…

  18. I got an order of Oxypetalum caeruleum seeds from GeorgiaVines and am ready to start them but am having some trouble figuring out the best way to plant them. I followed your advice on presoaking seeds for my Tropical Milkweed and they are doing great. I am considering pre-soaking the Tweedia, too. Will that work for them as well? I have gotten some conflicting info on how to start them. Do i really need “starting soil” for them? I used empty metal cat food/tuna cans filled with potting soil for my Tropicals in order to transfer heat to the soil easier. I’m in Tampa Florida so i’m going with no cold stratification. All of this is going in my little outdoor greenhouse. so far its all doing great. I also have a Balloon plant also that’s been supporting all the Cats and as they get big we are bringing them in to Chrysalis. I’ve eclosed 4 so far! Anyways, any advice on the Tweedia will help as I only have 10 seeds and want to do my best with them! Thanks for all the info on the site….its GREAT!

    1. Hi Tom, you would use the same soaking method that you used for tropical milkweed seeds. You don’t need seed starting soil if you are starting them outside. Keep in mind, I’m a Minnesota gardener so we take some extra steps so we don’t get too far behind!

  19. I just received my milkweed seeds from Monarchwatch. It said on the packet to use cold the seeds and It is April 29 and our last frost is the end of May. We are planting a Monarch Garden at our school and want to be ready by the last frost. Two questions: What should I do now and will they be ready in enough time for the Monarchs? Would I be better off buying some plants?

  20. 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!

    1. 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!

  21. 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…

  22. 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.

  23. 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?

    1. Hi Helen, I use the hydrogen peroxide on overwintering plants, not to start seeds. Here is more info on using the h2o2:

      Overwintering Butterfly Plants

      PS…I’m glad you were able to work out an arrangement with the seller for your milkweed plants. I hope that snow starts to melt soon!

  24. 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.


    1. 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

  25. 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!

    1. Hi Andrew, thanks for sharing you growing experience in Southern California. It helps to get tip/ideas from those growing in different parts of the country.

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