Seed germination disaster

[Lyril]

I'm in Victoria (Australia) and have been raising Wanderers for about 35 years. Last year was terrible - almost all my Fructicosa plants died suddenly after a long dry spell followed by heavy rain which flooded them. Lots of culling of caterpillars to save the few plants I had left, and a (fortunately) reduced population of butterflies. They usually arrive in January from South Australia I believe, and last for months.
So I decided to do a careful replanting. Lots of work tilling, building up beds, buying soil, setting up drip hoses and sourcing seeds. I ended up with - Asclepias curassavica, tuberosa, rotundifolia, incarnarta, syriaca and speciosa, mostly from UK. The theory was that a variety of plants would provide a backup if fructicosa died off again, and as some spread by tubers as well as seeds I thought there would be a double chance. No physocarpa - I'd tried those once and found too few leaves and too many pods before they all died off.

I varied the germination technique - some directly into the soil and some into egg cartons in my greenhouse. Some chilled, some not. And waited.

It must have been the worst germination result in gardening history. Of the hundreds of seeds I planted - not one incarnarta, tuberosa or curassavica germinated, fewer than 10 of the others and many of those didn't survive transplanting. Empty beds waiting for plants, and lots of fructicosa seedlings from last year have germinated in others. So I'm back to one species. None of those are big enough for food so I guess when the butterflies arrive and lay there will be mass slaughter again.

Has anyone any suggestions? I'm treasuring the few unusual plants to obtain seeds later on, and planning to buy more curassavica from NZ, - it's the only species banned by AQIS from UK or US. I wonder if the half-year gap in seasons may have had some effect. Or maybe just my lack of skill.

But how on earth can a plant that's classed as a weed species in some US areas be so hard to grow?

[Mona Miller]

The milkweed species that you are talking about are all north american. I'd try another tropical like the Asclepias curassavica. Tropical milkweed is really easy to grow.

[blazing star]

Based on my native seed catalog (I'm in the U.S.), they reference that milkweed seeds need a 30 day period of moist, cold stratification. You can manually force this upon the seeds by putting the seeds in a plastic bag with a moist medium. I've inquired with the vendor about this and the medium should not be so wet as to total, wet saturation that can be rung out. Put this in the fridge for 30 days and just keep an eye for germination in the bag. You can then transplant as desired. Again, this is for milkweed native to the U.S. I'm not sure if seed sourced from the U.K. has evolved to require this same environment to germinate.

I've used this technique in the past and am not sure how well it works if you simply sow seed about since the seed hasn't had time to work its way into the soil and set root as it germinates. Here, the fluctuations of heat and frost help work the seed down into the soil so that it sets root and can thrive. You'd probably be better off putting the germinated seed into pots and keeping an eye to make sure the seedlings don't dry out.

I hope this helps. Best of luck to you!