Starting Milkweed Seeds Indoors Part 3

ByTony Gomez

The Final Results Are UP

It’s been a couple weeks since we started annual milkweed seeds and it’s time to report results. If you haven’t read parts 1 and 2 of this seed starting journey, click the links below to start from the seedy beginning:

How to Start Milkweed Seeds Indoors I (Why Should You Start Seeds Inside?)
Starting Milkweed Seeds Indoors II (Discover My Secret for Lightning Fast Seed Germination)

Results

  • 8 new Gomphocarpus physocarpus (balloon plant) seedlings. The balloon plant seeds in the smallest container germinated first….probably because the heated seedling mat warmed the soil faster in a small container.
  • 3 Giant milkweed seeds soaked overnight in water germinated…our first ever giant milkweed seedlings.
Asclepias Gigantea (Giant Milkweed) Seedlings Started Indoors
  • None of the unsoaked giant milkweed seeds germinated…hoping they will with more time.  Soak your annual milkweed seeds! (and seeds in general)
  • Next time, I’ll use smaller containers or seed starting trays to enhance heat effect (not gallon milk jugs).
  • Sprayed seedlings with hydrogen peroxide mixture I’ve been using on overwintering plants. Plants seem to respond well to h2o2!
  • Satisfied with these results…just not sure where I’m going to put all the balloon plant milkweed, since we already have 3 large plants.
  • Will update this section with any further developments

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Results & Comments

Starting Milkweed Seeds indoors? Swan and Tropical Milkweed are great options for starting indoors early since they'll both flower and seed in one season
Baby Milkweed

First off, I’d like to report that there was a previous error in this post. The milkweed species below is Gomphocarus Physocarpus, commonly known as balloon plant. I’m leaving this here to show you how well my seed starting technique worked for this species:

Here are some ‘mixed’ results on a few different milkweed species:

1. SWAN SONG: I started giant swan milkweed seeds (Gomphocarpus physocarpus) that I purchased online. I enjoyed great success and all 7 of my plants eclipsed 7 feet! In the fall, I was able to harvest seeds from them to use for this season. Here are the final results from my gathered seeds:

  • 10 seeds planted
  • first seed germinated after 4 days
  • 100% germination
Goose Plant Milkweed Seedlings after just one week
Not Swan Milkweed, but actually GIANT Swan Milkweed aka Balloon Plant!

I’m happy I collected seeds last fall. It certainly paid off this season, and those seeds should be viable for years to come!

Sad Seeds ☹️

(Please be aware quality seeds for the following are much easier to source in 2024)

Once again, when I opened the package of my Calotropis gigantea seeds and was appalled by the condition of the seeds. They seemed small and  they looked old and brittle. My first reaction was to toss them but realized my gardening predictions had been wrong before so I planted…0% germination rate again.

Here are the sad results from a couple of seasons ago:

2. TARNISHED CROWN: Calotropis gigantea (crown plant) is a giant milkweed variety with lots of thick leaves for monarch cateprillars. This is native to warm weather regions including Africa/India and commonly used by Hawaiian monarchs. None of my regular sources had these hard to find milkweed seeds at the time, so I took a chance on an unknown vendor.

The seeds I purchased looked old and immature (kinda like mini Benjamin Buttons), but I’d never grown them, so what did I know?:

  • 16 seeds planted
  • first seed germinated after 5 days
  • less than 1% germination
  • I started the remaining seeds yesterday…hoping I can salvage 2-3 plants for the season out of 50 seeds

I’m very disappointed with these results, but I’m more disappointed that this company is ripping off the gardening community with subpar seeds. If you are thinking of buying milkweed seeds or plants, check out my list of reputable online vendors. (This company won’t be making that list anytime soon.)

Also, in northern regions, I highly recommend starting with plants or stem cuttings for the calotropis varieties.

Another Option?

I didn’t start Calotropis procera seeds this season, but they are a good option for overwintering plants indoors if you live outside of their perennial region

Our procera seed starting was very successful in past seasons:

3. TREE OF LIFE: When I was researching sources for buying giant milkweed, I came across a similar species of milkweed I had never heard of before. The milkweed tree (Calotropis procera) is also native to Africa but a rare find across North America. I decided to give procera a try since it’s reported be both a host and nectar plant for monarchs,  but would these seeds be as disappointing as the last?:

  • 10 seeds planted
  • first seed germinated after 5 days
  • 100% germination rate
Starting Milkweed Seeds indoors? Start Warm Weather Milkweed Varieties 2 months before your avg. final frost for a huge head start on the season...and the monarchs!
Little Trees of Life

More Starting Milkweed Seeds Inside Results

4. The REAL Swan Milkweed:

Swan milkweed is an annual milkweed for northern regions that is proving to be a valuable host plant for monarch butterflies, but only if the seeds are started early indoors. Otherwise, the plants won't grow large enough to sustain monarch life. More info on starting milkweed seeds indoors...

For the first time, we started Gomphocarpus fruticosus (swan milkweed) this season. These plants are similar to the balloon plant mentioned above, but they have a shorter, bushier growth habit.

I receive these seeds as a gift and am not sure how old they are. Only 6 total of 15 seeds germinated, but the seedlings look healthy so far. Unless these seeds require different treatment than their balloon plant brother, I’m guessing the seeds might be a few years old.


The One you can Count On?

5. Tropical Milkweed:

The only seeds with a high germination rate were the tropical milkweed seeds. I had harvested the seeds from our garden in 2012 so I was hopeful they would still be viable. Below is one of the milkweed seedlings on what looks to be a tropical island, but the sand is just an added layer of protection against fungus gnats…

Starting Seeds Indoors? A light layer of sand can trick those pesky fungus gnats into thinking the soil is dry. It's also a natural treatment that won't leave chemical residue in the soil.
Dry Soil?…or Fungus Gnats Foiled Again!

You can also take cuttings from overwintered plants in spring to multiply your milkweed supply.

Tropical Milkweed, Balloon Plant, and Calotropis Procera seeds all have high germination rates using the germination techniques outlined in this 3-post series.

In the years of seed starting since these first experiments, I’m happy to report it’s easier to find viable milkweed seeds of some of these lesser know varieties. The milkweed movement continues to grow because of home gardeners who are passionate about supporting monarchs.


Conclusion 

With over 100 species of North American milkweed, each year brings opportunity for new growth…and more monarchs! While native milkweed species are the cornerstone for a successful butterfly garden, you’ll benefit more from starting annual milkweeds indoors since they need to flower and seed in one season.

More Questions or Comments about Starting Milkweed Seeds Indoors? Please Read through the comment section below:
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29 Comments

  1. yes Georganne…you can plant them. Light fertilization after two weeks should be fine. I would wait about a month before pinching off leaves. Regardless, tropical milkweed is resilient…

  2. Also, if I go ahead and plant them now, is it too early to remove the inner leaves so they will branch off? Also, 2 weeks after planting I would like to fertilize them Any thoughts?

  3. I have tropical plantings that have their second leaves. We are in Daytona Beach and there is no real chance of any frost. Is it ok to go ahead and plant the seedlings this early?

  4. I planted some tropical milkweed seeds. 4 of 6 germinated. After 3 days, they all fell over. I have been misting them with a spray bottle. What have I done??? Will they bounce back?

    1. Hi Jenny, to create stronger stems you can try an oscillating fan. Do you have sufficient light? In Minnesota, we start tropical seeds in sowing containers, which gives them a slight head start with minimal care:

      Spring Sowing Containers

  5. I just received some annual milkweed seeds. Should I start them indoors now? My apologies but I can’t seem to find your starting date . Thank you. Maine, zone 5

    1. yes Rachel, I would start them now to extend the growing season. Typically, I do this (in Minnesota) around the beginning of March, but doing it now should still make a noticeable difference. good luck!

  6. Hi Tony,
    I was wondering if you could share with us what type of sand you use and when do you put it on the soil to deter the fungus knats?
    Thank you so much for all you do. 🙂

  7. Hmm did I miss something? I’ve scanned all three pages of How to Start Seeds and I can’t find anything that says what type of soil to plant the soaked seeds in. Sorry if I missed it!! I also saw that you sprinkled sand on the surface, as well?
    Thanks

    1. Hi Susan, I use a typical seed starting mix that you would find at local nurseries or big box stores. I don’t mix in any sand.

  8. i have a lot of milkweed seedlings about two inches tall and very leggy but upright. they are in those small cube planters,less than an inch square. Is it too late to plant these now? 7/21

    1. Hi Luther, the dog days of summer are usually not prime time for planting fragile seedlings, but if you keep a close eye on them so the soil doesn’t dry out they might be OK. Spring and late summer (when it starts to cool) would be better times for planting seedlings. good luck!

  9. Hi Tony,
    I would really like to try Tithonia Torch this year. I live in Cleveland, OH and am wondering if I can direct sow these in May or should I start them inside?
    Thanks,
    Chris

  10. I am starting my tropical milkweed seeds tonight. Going to soak them and I bought a starter kit with a heater. Hope it goes well. I’m excited I’ve never started seeds like this before.

  11. Hi Penelope, congrats on all your new plants! You might want to find some small pots and maybe put six in each one so they have room to grow…otherwise you will probably lose some plants if they’re growing on top of each other.

    Your other option is to just pinch off the plants that are going to be “problem” plants so that they all have room to grow. You’ll lose a few plants, but it’s less work for you.

  12. I am near Lake Tahoe, NV. I collected some showy m/w seeds from a roadside in my rural area last year. I planted them in 4 gallon milk jugs almost 3 weeks ago. They didn’t all germinate but I have over 60 with second leaves starting. I won’t be able to plant them in the garden for at least 2 months as we are warned of frosts up to early June! I can see thru the plastic that the roots are very long already. Will the do ok if I keep them in the jugs for that long? Their little roots want to go deep. I will again collect my caterpillars from the roadside patch of m/w and hope the farmer won’t be spraying them. I would speak to him about it. He may not even know he has m/w but you know people can be contrary and he might then spray on purpose!

  13. Tony,
    Thanks for your update on your seeds.
    Do you think if I start my seeds and put them under T5 grow lights that it would be alright for them?
    Would like too start a couple dozen for Garden Club plant sale in May .

    1. Hi Judy, I was thinking of trying that with my seeds that haven’t germinated. I have never started under grow lights, but perhaps it will shock some of the more questionable seeds into sprouting. I can’t think of any reason it would hurt them…I will post an update when I do this.

  14. I started a community garden in inner city Youngstown, Ohio. I have only grown or planted common milkweed but got some tropical seeds this year. thanks for the information. I am planning my 3rd annual Butterfly festival and think this will make a great addition. the kids love it. most of them had never seen or fed a live butterfly before. I am going to try and tag some this year as well. became a monarch waystation.

  15. Hello, I see these are older post and hopefully you are still doing the wonderful job of saving the monarch. I live in the panhandle of Florida and I just begun this challenge. I have order the milkweed plant as well as some seed. Hopefully I can get them t thrive. I have not been as active in my garden this summer as I usually am but plan to jump back in shortly. I thank you for your post and now feel a little more positive about being able to grow the food for the monarch. as well as any other butterfly that wants t stop for a visit. Again thank you and any info would be greatly appreciate.

  16. Thought I’d let you know that about 4-5 years ago and again last year, I bought some blowefloodrs at my local greenhouse. I like to try new garden plants every year. The bloodflower is related to the milkweed but are annuals in our climate zone (North Dakota). Monarchs were attracted to them and I saw several monarch caterpillars, one of which spun its cocoon. I kept a close eye on the cocoon but missed the emergence of the monarch. I saved many seeds from the plants but sent them all to my dad in Idaho. As a family, we collected butterflies during my childhood and my dad is passionate about helping them out when he can; due to the lovely progress of civilization , natural habitats of insects and other wildlife is continually being disturbed and destroyed.

    1. Hi Katerina, I think you’re the first person from North Dakota I’ve come across that grows tropical milkweed. It’s an excellent annual for colder zones. Great to hear your family is so passionate about helping monarchs. Happy gardening!

  17. Hi Lila, I typically use a a “seed starting potting mix” because there aren’t large particles that could block root growth. Once there are a couple sets of leaves I’ll add a slow release fertilizer (I use osmocote).

    My annual milkweed varieties have responded very well to the nitrogen boost they receive from this fertilization.

  18. Thanks for sharing! What soil do you use for starting seeds?

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