I am always delighted to see this growing along the road in front of my hedge (and somewhat inside the hedge) as it is rarely seen in my area anymore. So I encouraged it for the last four years or so, the same few plants growing in the same place. Well, this year there were two young plants growing in my flower border, some in the orchard and some along the property line and the back yard. When a gardening friend saw the ones in the flower bed she told me that they will become a nuisance because they spread by runners. Is that true? I thought it was by seed. So I tore them out. I didn't see any or much root attached, so perhaps there are runners under the soil now?
I have some hybrid milkweed in a spot in the orchard I bought at a nursery, totally different foliage and stalk than the wild, and it hasn't spread. I really like milkweed because of the butterflies, and I've even seen birds using the silk to build nests (saw orioles one year doing this with the previous year's seed pod silk).