Chamberbitter (Mimosa Weed) – Identification and Control
In order to respond to the many garden questions I receive, I’ve assembled a crack team of Master Gardeners to help me. Theresa, Stacy, Caryn and Shannon have myriad different garden skills and interests and I can count on them to know the answer to most of the queries we get via e-mail.
When Stacy e-mailed all of us a panicky personal question a few days ago, I knew it had to be a stumper. “Help! My lawn has been invaded by little mimosa seedlings. I have tried everything to get rid of them but nothing seems to work. Are any of you familiar with this weed?”
Familiar?? Heck, I’m on a first name basis with this pest. My neighbor Gus brought it to my attention a few years ago in his lawn. Now he spends a half-hour each week pulling it from his flower beds and his fescue.
The weed has a tongue-twisting name: niruri (Phyllanthus urinaria). In later years, scientists have started calling it chamberbitter but under either moniker it can be a major nuisance in your landscape. Niruri in Spanish literally means “break stone”. The mature plant is a small shrub which grows widely in South America and Asia. There, it is used as an herbal remedy for kidney stones. In my lawn, constant mowing keeps it three inches tall and looking exactly like a mimosa leaf.
The yellow, ball-like seeds of niruri develop under the leaves. They need very warm soil in order to germinate so you won’t notice the seedlings until mid-summer. Researchers say pre-emergence herbicides that contain atrazine (Purge) on centipede lawns and isoxaben (click for sources) on all turfgrasses give good results when applied in early May.
Glyphosate (click for sources) will kill it but you have to be careful to keep the chemical off nearby foliage.
Horticultural vinegar (20% acetic acid or higher, dangerous) or horticultural soap (not dish detergent) are organic alternatives.
Like my neighbor, you may find that simply pulling out the weed gives good enough results. Be sure to discard the plants immediately; don’t put them on your compost pile. Whatever you choose to do, though, don’t let this tongue-twisting pest become well-established unless you enjoy back-breaking labor!