Tropical Milkweed (Red) Germination Time?

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  • #56604


    Hi folks,
    My good friend & I are embarking upon a project to grow Swan Plants. I harvested some seeds from the Meola Rd, Soccer Field carpark which we have sown and speedily germinated, approx 150 each.
    From this website we saw and purchased some of the Red milkweed seeds (Asclepias curassavica or Tropical Milkweed) which we sowed 2 weeks ago.
    The germination rate has been disappointing with 3-4 sprouting out of 36 seeds we sowed each.
    We used the same procedure as we had for the common white Swan Plants.

    – What is the expected germination time please?

    – Are we doing something wrong?

    We even took the precaution of swapping a tray of seeds (in a pod of 6) with each other in case of climatic disaster. Well we both have one seedling from each other out of the 6 seeds. Most disappointing.

    We noted the shape of these red plant’s seeds are different to the White Swannies. Very flat, like a ‘flake’.

    Are we expecting too much, too early? Is a 10% germination rate normal or poor?

    We are on opposite sides of the Harbour Bridge.

    Thanks for any insight you can give us.

Viewing 7 replies - 1 through 7 (of 7 total)
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  • #56637


    Hi Caryl. Thanks for that snippet. We’re still getting 20C+ days in AKL and ‘cold isn’t expected for some time.
    I’m just home from a weekend away and now have 8/36 germination. So the Plan ‘A’ is still in-play.

    “Cold stratification” is now on my radar…




    I thought most swan plants seeds need cold stratification (moist or dry) which increases the germination rate. I don’t favour tropical milkweed.I had it for a season and it spread sideways and hardly grew much at all and little value for monarch caterpillars. Caryl(Wellington)



    Thanks, Milkweed, so much, for your input. Our seeds are in the potting mix for 2 weeks now so thete’s no going back.
    I have 6/36 seedlings germinated and placed in the sunny spot for daily warmth.
    Will just have to wait and see what happens over the coming days for the tardy 30/36.
    Best regards,



    It’s the wrong time of year to be growing Tropical milkweed (Asclepias curassavica) in NZ. I firmly believe that Swamp milkweed (Asclepias incarnata) is more suited to a lot of parts of NZ because the climate just isn’t hot enough for long enough for Tropical milkweed to thrive in generally. It’s a pity the seeds of Swamp milkweed are not more readily available because it also has quite stunning flowers in both white and pink varieties. I’m sure others will disagree but this is my overall experience using many different milkweed species in the Manawatu.



    Thanks for the swift responses Leslie & Jacqui. Much appreciated.
    Well, we have sown all the seeds so we have to cross our fingers, eyes and legs.
    In Auckland it’s still 21C daily and no lower than 12C overnight so I think the temp isn’t too bad?
    We both have a sunny spot for them. No hot-house or heating pads but I have plastic ‘takeaway tray’ lids over them to act as mini-hothouses. That worked for the Swannies.

    It was the bright colour of the red flowers which attracted us to the idea of growing them. We had only ever thought White Swan Plants were the single food for Monarchs. After scouring this site we found the red, yellow and even the purple plants. Very exciting.

    In the meantime, patience is hopefully a virtue. Maggie may have some thoughts to add. I’ll report back in a few days.



    I’m in Wellington and I don’t bother trying to grow plants after late January. I’ve found the chances of success depend on length of daylight and warmth. And the seedlings are prone to mildew and slugs and snails. The tropical seeds seem to take longer to strike and in my experience are less viable than seeds for the standard swan plant. I have a hothouse but overusing that ups the chance of mildew. Its definitely a better bet to wait for the warm temps and longer days to get good healthy outdoor plants.



    A. curassavica likes warm soil so germination could be slow or erratic as the weather is getting cooler – remember that it is a tropical plant so you would probably do better sowing the seeds in the spring when the soil is warmer. However, as you have already planted it (and if it is in flats or pots) I suggest you put them in a warm location – full sun or if indoors in a window or on a heat pad.

    They usually take about 2-3 weeks, so don’t give up on them!

    Yes the seeds are quite different to swan plant seeds. Asclepias spp. come from North America. Swan plants (Gomphocarpus spp.) come from Africa.

    If you still have seeds left, wait until spring. Start them indoors in September. Just lightly cover them and keep moist. They can go outside after the danger of frost has past. Plant them about 300mm apart and you can pinch them back to make a fuller plant.

    My own plants are doing really well this year, with climate change I suspect. I have them in pots in full sun.

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