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?