Every Summer Ottawa lawns begin to start turning lime green around the edges and in spots throughout open spots.  Upon closer inspection, you will find that a new type of unsightly grass is growing within the lawn: Crabgrass 


Crabgrass is often a symptom of a thin lawn or an underlying stressor (like grubs or chinch bugs).  Crabgrass springs up anywhere there is a hole in the lawn and the soil is warm.  Since heat stresses normal turf, you will see stressed lawns along roadways, walkways, drives and curbs. These surfaces absorb and radiate heat, intensifying the stress on the turf and making it more vulnerable to damage.

 

Identification

  • Crabgrass is a warm-season annual which germinates in late spring and grows throughout the year dropping its seeds in the fall and then dying after a couple of frosts.
  • It grows low to the ground and spreads out in a dense mat which crowds out healthy turf type grass.   
  • It is lime green, grows in sunny spots and along curbs/sidewalks.  
  • You'll start seeing it in late May or June once the soil temps reach 55f/13c


Young Crabgrass PlantYoung crab grass.  Pulled before going to seed.


Prevention

  • In Ontario, A thick well watered lawn is the best defense against crabgrass.
  • With the cosmetic pesticide ban in effect, there are no effective pre emergent herbicides which we can apply to prevent crabgrass.  
    • Home owners can try applying Cornmeal gluten which is sold in the spring at big box stores.
      • There is mixed research on whether cornmeal gluten is effective at preventing crabgrass seed germination
      • We do not offer this service, since we cannot currently stand behind the product. 
  • Heavily overseed thin spots in the lawn
    • this keeps soil temps lower and prevents crabgrass seeds from germinating.


Removal

  • The best way to remove crabgrass is to pull it out by the root. 
    • You can clear about 1.5 sqft of lawn every 5 min, or about 15-20 sqft of lawn every hour
  • If the crabgrass is a full mat and there is no good grass remaining, a non selective herbicide can be sprayed
    • This must happen BEFORE seeds are on the plant. 
    • Since grass seed may not germinate in the summer, it is best to repair large spots in the Fall
      • This approach will leave large dead spots in the lawn until repairs can be made in September.
  • A sod cutter can also be used to remove large sections of crabgrass.


Repair

  • Add seed in the holes created by pulling the crab grass.
  • If large sections of crabgrass have been removed or killed, slice seed the affected areas.
    • Sod is also an option if a sod cutter has been used



Additional Information: