Crabgrass or Quackgrass


by Karen Weiland, Advanced Master Gardener




No matter what the differences are in these two weeds, they are both a pain in my lawn and although they look somewhat alike, there are differences.

To remember which grass is which, I relate crabgrass to a crab with its’ outstretched legs and the way it grows flat against the ground. Quackgrass grows in an upright fashion like a duck (quack) with its’ long neck in the air.

Quackgrass is a cool season (cold hardy) perennial weed which means it will grow back every year.  It reproduces from seed and long underground roots called rhizomes.  Weed killers will set it back and so will mowing it to a very short height in the spring.  Quackgrass relies rather heavily on the food stored in its root system.  The earlier you mow it down to the ground in the spring, the less it can build a food supply in its roots.  Spot treating with glyphosate can be used to help get rid of quackgrass.  The best time to apply it is when the mother plant is young, actively growing and not under drought stress.  It may take several applications to kill it.

Crabgrass is a warm season annual (grows from seed during the warm months).  Crabgrass will take over in bare spots and in areas where turfgrass is weak.  Unlike my tomato plants, crabgrass is not picky about moisture, pH levels or fertilization.  It will grow anywhere.  Each crabgrass plant will produce thousands of seeds each year and those seeds can be viable for years.  One way to discourage crabgrass is to bag the lawn clippings starting in August and going through September when crabgrass goes to seed.  This will help to keep fresh seeds off the lawn.

Getting rid of crabgrass has given way to an entire product category, the pre-emergent crabgrass killer.  A pre-emergent will prevent emergence of crabgrass plants. In this area, a pre-emergent herbicide should be applied in early spring before crabgrass sprouts and that can happen as early as the middle of April.  Purdue research has shown that these herbicides can be applied as early as March 1 and still get the job done.  A drawback of using pre-emergents is that it affects all grass seed for up to 12 weeks after application, therefore it cannot be used when seeding a new lawn.  Post-emergent grass killers are most effective when the plant is still small.  Always read, understand and follow all label directions.

Healthy turfgrass is the best deterrent to either quackgrass or crabgrass.  It is especially important for turfgrass to have a deep root system since this is a leading defense against summer drought.  A drought can kill grass and create openings where both of these weedy grasses along with a host of other undesirable weeds can get a foothold.

Good lawn care begins with a soil test so you know what it needs in the way of fertilization to be healthy.  Fertilization helps to produce thick, vigorous turfgrass, making it hard for weeds to grow. Set your lawn mower height at 3 to 3 1/2 inches and never remove more than 1/3 of the leaf blade when you mow.  Yes, you may need to mow twice a week when grass is growing fast.  There is a direct relationship between grass tops and roots.  The taller the grass plant means more and deeper roots, which in turn means the grass plant can withstand stress better.  Taller grass also shades the soil resulting in less moisture loss.  Water deeply and infrequently.


As always, Happy Gardening!


More information about gardening and related subjects is available online at  The Purdue University Cooperative Extension Service can be reached at 499-6334 in LaGrange Co., 636-2111 in Noble Co., 925-2562 in DeKalb Co. and 668-1000 in Steuben Co.