Gina says September 10 at 4:40 am I have switched five caterpillars from one milkweed to another and my babies haven’t moved since. But, stratification wouldn’t hurt the seeds of Butterfly Weed at all, and might even increase the germination rate. My good intentions to help preserve the Monarchs by buying tropical from HD was rewarded by getting tons of cats and all of them died in a few days and a few lasted a few weeks before dying off. Also effective in sunny borders. But it seems the older they are, the easier the switch.