Personally, I would not cut them back. During the migration, Monarchs can use nectar from many different plants.,so, they don't need to depend on milkweed blooming. The milkweed need their leaves left to absorb sunshine and transfer energy down into their roots for next spring.

Martha

OK thank you!

Those are beautiful plants! Even more reason to not cut them back.

Thank you. They sure grew fast this yr.

Advice from some of the monarch experts is to cut them back to about 12" in late spring to encourage bushier growth and plenty of tender young leaves for late-season caterpillars. Of course it's too late for that this season.

I've read that cuttings of most milkweed root quite easily. If so, they could serve to expand the garden or give to someone else. I've not tried it ... yet.

During the fall migration, don't the Monarchs again lay eggs to create new generations to return to Mexico? I've found eggs and raised young Monarch cats during late summer, early fall here in central Arkansas. I assumed the eggs were laid by Monarchs migrating back toward Mexico from northern states.

...Mary

I second Martha's comments above.