Please find attached picture. This weed takes over my garden usually in July despite that I have ground cover like Thyme, Phlox, Sedium etc. It is killing me. What is the name? are they perennial or annual. How to prevent them from coming back. Thank you so much.
Hello! Thank you for reaching out to the Toronto Master Gardeners. I am afraid that your unwelcome weed is crab grass. It is a truly aggravating weed and difficult to control, but with persistence you can keep on top of it. Crab grass is an annual weed, it is spread by seed. Unfortunately, the seeds can lay dormant for several years, so this will not be a one season project! Hand pulling is the best solution, but it is key to pull BEFORE it goes to seed. I understand your strategy of ground cover to help with this problem but seed can still germinate between your plants. You might want to try the solarizing method. You will need to clear and then wet the soil around the crab grass-you then lay a clear thick plastic sheet over the area, anchor the edges well with heavy stones or bricks to keep the sheet from moving and leave for at least 2 months. During that time the sun will heat the area around the weeds and kill by “cooking” the seeds. There are many questions about this on our website if you search ‘crab grass’ or ‘solarization’
After, cover the area well with mulch and quickly hand pick any sprouts of crab grass you see.
I wish you luck with this truly difficult weed!