There isn't a hurt in leaving the plant stalks in place, even though this encourages rampant self-seeding, which is often not wished-for. Do not mulch above the basis crowns, as This will boost rot. I dug up alot of these very last yr, bur they keep appearing in all places https://is-milkweed-a-flower99988.blog-a-story.com/11217206/considerations-to-know-about-is-swamp-milkweed-a-perennial