Butterflyweed (Asclepias curassavica), also called tropical milkweed, silkweed, Mexican milkweed and bloodflower, is a species of milkweed that is hardy enough to survive in most parts of the United States. Cutting back the plant helps control overgrowth and keeps it in bloom, and pruning should take place at different times of the year -- between late spring and late fall, and ending before any major snowfall in your area.
Cut dead branches off the plant in late spring. The Butterfly Bushes website recommends doing this in June. Worthington City Schools in Ohio suggests trimming 50 percent of the milkweed back by half at this time, too.
Deadhead the plant every couple of weeks in summer. This will let the plant continue to concentrate on flowering instead of producing seeds.
Trim the entire plant back to less than 4 feet high in late fall.
Inspect the plant every year to find older stems that now appear "woody" toward their bases; cutting these off at the base of the stem will let the plant produce new growth.