I, too, mow around any of the milkweed-like plants on my property. It seems to be improving the populations. Not quite as fast as I'd like, but I get a few more every year. I leave my flower patches that have been mowed around until late winter/early early spring before mowing them down. I am betting the seeds do better on the dead plant through the winter than mowed down and left to settle into the grasses for the mice and bugs...I don't really know, but it's what I do.
