How do I renovate a rain garden that has become overgrown with weeds?

Asked September 13, 2014, 12:10 PM EDT

I am working on a 5-year-old rain garden at a school that was never taken care of it. I am clearing out weeds, etc. and I have two questions. 1) Should I cut it down to the ground this fall? It is spindly (some kind of grass has overtaken it) and needs some revitalization. 2) What is the best way to remove invasive thorn plants? I have removed them so seeds would not spread, but they will obviously sprout again. How do we try to get these to go away as best as possible? Note: I have removed weeds and tree saplings that do not belong.

Dakota County Minnesota

1 Response

Thank you for the question. You did the right thing by removing seed heads, weeds and saplings. Hand removal is still the best way to remove these unwanted plants because herbicides can harm desirable plants and beneficial insects. It is best to delay cutting down the desirable plants until next spring. This provides food and habitat for many species of birds and small mammals. Also, leaving your plants up for the winter can create winter visual value.
Next spring, watch for the thorn plants to sprout and periodically cut them off at ground level. Eventually, they won't have the energy to grow anymore and your desirable plants will begin to out compete the weeds. A 3 inch layer of mulch, usually a hardwood mulch that won't float away, applied this fall will help prevent new weeds from sprouting next year.
Here is a link to Metroblooms guide on rain garden maintenance:
Here is another link to the University of Wisconsin Extension rain garden information. The entire publication is very good, but you can scroll down to page 17 where is talks about rain garden maintenance: Good luck and thanks for contacting us!