The Cut That Tames Milkweed and other Tall Plants

Common milkweed (Asclepias syriaca) elicits a lot of reactions from people.

On one hand, it is an essential host plant for monarch butterflies, a valuable nectar source for bees and other pollinators, and an abundant bloomer in June and July. It is also remarkably easy to grow.

On the other hand, common milkweed can spread aggressively into fields and pathways and can be difficult to remove. By late summer, it often becomes sooty, insect-covered, and floppy.

Connecticut Agricultural Experiment Station entomologist Kelsey Fisher, Ph.D., is studying whether common milkweed can benefit from a “Chelsea Chop.” This is the practice of cutting perennial plants back by one-third to one-half in late May or the first half of June to reduce overall height, delay flowering slightly, and encourage sturdier, fresher-looking growth later in the season.

Fisher’s inquiry centers around a possible timing mismatch between milkweed blossoms in CT and the optimal time for monarch visits, but it could also help us avoid sooty, floppy milkweeds.

“Typically, monarchs aren't found on plants that are covered in aphids and sooty mold, but sometimes they are,” she says. “Both adults and larvae tend to prefer young, fresh, happy-looking plants and leaves.”

She continues, “You must clip the plants back before they look bad. Bad-looking milkweed likely won't put out new growth. We're still working on figuring out the timing, but ideally, [after an early cut], the leaves will grow back and make the plant preferable for egg laying.” (Kathy’s note: And look better, too)

Many perennial plants respond well to this kind of early-season pruning. Cutting stems back by about one-third in late May or early June — before flowering begins — can produce shorter, sturdier plants with prolonged bloom and improved appearance. At that point in the season, plants may only be one-third of their eventual height, but the pruning guideline still applies.

Here's a list of eastern U.S. native plant genera that may respond well to a June cut, organized by common name and genus.