Answer: Milkweed, (Asclepias) can be difficult to get started in the garden, as you have experienced. Once established, however, it can be difficult to eradicate and may spread if it is happy. Note that it is very slow to emerge in the spring, so you need to mark the spot where it grows. It has a tap root which can make it difficult to transplant, although smaller plants started in containers seem to transplant more successfully or you can try to propagate it by root cuttings. Also, if you tried to grow Swamp Milkweed (A. incarnata) it may have sulked because the location you planted it in was too dry. (Other milkweeds seem to prefer a better drained site.)
Seed germination varies depending on which type you have. For example, A. incarnata and A. tuberosa (Butterfly Weed) seem to germinate erratically but sometimes as fast as two weeks, A. speciosa should go very quickly, and A. pupurescens needs a 12 week cold startification period. Good luck with your milkweeds!
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