name that weed: pilea pumila, or clearweed

FINALLY: GOTCHA! For decades each summer I have pulled thousands of self-sown seedlings of a plant whose name eluded me, but whose habit and appearance were all too familiar. I’d come upon one stand after another, summer after summer, lurking in masses under shrubs and trees and even under large perennials. But what was its name? And now I know: It’s clearweed, or Pilea pumila, a cousin of stinging nettle (Urtica dioicia) but minus the barbs, and a North American native. A little about Pilea pumila, and about learning to name–and tackle–your weeds. And also why to sometimes leave a little for the native insects to enjoy.

I knew my garlic mustard from lamb’s quarters or mugwort, wild grape from bittersweet or Ampelopsis, oxalis from everything else. But clearweed kept me in the dark longer than most. I could have guessed at its common name, since the stems are practically translucent, or clear. And no wonder I have so much of it: It favors moist soils such as mine generally is, and shady and semi-shady spots in or near woodlands such as the one I garden on the edge of.

The USDA conservation map show the presence of Pilea pumila in 38 states, and parts of eastern Canada. The Flora of North America (efloras [dot] org) says that Native Americans used clearweed medicinally, “to alleviate itching, to cure sinus problems, and to treat excessive hunger.” The Illinois Wildflowers website notes that certain native insects use the plant, too. All these years, the only thing I thought it was useful for? To aggravate me.

Turns out various caterpillars of moths and butterflies enjoy it as a host plant (they’re listed here and include the comma and the red admiral), and so my new policy is to leave a couple of out-of-the-way patches of clearweed to develop at my place. I still pull it from the more formal garden beds.

pull weeds now, or else

I BRING UP A WARM-SEASON WEED like this right now (high summer/early fall) for two reasons: There are probably a lot of them in general in our gardens, and specifically because a lot of them are about to go to seed as in the detail photo above. Pull now, or expect more next year.

My cardboard technique for making new garden beds can also work for weed-control, and I sometimes spot-smother smaller areas when I can’t keep up with the pulling or digging. Pilea pumila, unlike some of my other more firmly rooted opponents, is easy to slip out of the ground without tools, particular after a rain. Place seed-laden or rhizomatous weeds in a large plastic bag first, to cook them to death, before incorporating them into the compost heap.

identify your weeds

KNOW THY ENEMY. After all, how can you outsmart a plant whose habits you don’t even understand? I think success starts with proper ID, and my article on how to identify weeds, including links to many online tools, can help you get to know yours. Don’t wait as long as I did with clearweed; don’t give them the upper hand in garden beds. Again, however, I leave some clearweed on the looser fringes of my property–as I do with another native “weed,” jewelweed.