Lawn weeds and Overseeding question #357044 - Ask Extension


Lawn weeds and Overseeding question #357044

Asked August 27, 2016, 11:00 AM EDT

I have some patches of heavy crabgrass and what looks to me like Prostrate Spurge (possibly Prostrate Knotweed) taking over my front lawn near the street. Its gradually moving inward and taking over more of my lawn. This area is subject to lots of sun! I'm wondering, is overseeding a good idea? After some thorough research, I'm thinking of renting a slit seeder next week (right time of year to overseed?) that will agitate the soil beneath the crabgrass & broadleaf weeds and deposit grass seed in the soil near the surface for good germination, and then water 4 times a day (I have underground sprinklers in that area). You can see in the photos the area it is taking over (bottom of 1st picture), and close ups of the weeds. Is it recommended to kill the weeds before overseeding? Looking for your expert advice for my situation. Thanks so much for taking time to help me!

Anoka County Minnesota

Expert Response

I think you are correct in your identification. To differentiate between prostrate spurge and knotweed, break off a stem and if it is spurge it will leak a milky sap.  New grass will not out compete the weeds. Using a pre-emergent herbicide in the spring will keep the weeds, all three are annuals, from resprouting. If you overseed in the fall scrape off the weeds so the grass seed is in contact with soil. This is necessary for germination. Watering once a day should be adequate and water more if the soil is drying out. If the area is watered too much the seed will rot. Fall is an excellent time to repair a lawn. Please see the fact sheet.
Claire Kari Replied August 28, 2016, 9:34 AM EDT

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