Crab Grass

(Question)

Over the last two years I have reseeded my friend’s lawn (which is quite small) with a grass mixture (rye, fescue, bluegrass) however half the lawn is thick with crab grass. The other half of the lawn, which is shaded by a birch tree, doesn’t have the same problem with the crab grass. Would you suggest digging out the crab grass part of the lawn (approximately 50 square feet) and laying down sod?

(Answer)

Crab grass is a common problem in home lawns.  It is an annual weed which reproduces by seed and thrives in sunny areas and high temperatures continuing to germinate into July.  For this reason, the shadier area of the lawn is not experiencing the same issue. Crab grass germinates quickly so easily outcompetes grass seedlings in a newly seeded lawn and fills bare spots in an existing lawn. Hand weeding is an option in a small lawn but will not resolve the problem in a single year as the many seeds produced in mid to late summer will survive in the soil for several years.

What you are after is a thick turf which will shade the soil and reduce the number of crab grass seedings that are able to establish.  There is no easy answer as to whether sod or seed is the better approach to meet this objective.   Information on the pros and cons of each approach can be found in our post at the link below.

https://www.torontomastergardeners.ca/index.php/askagardener/reseed-or-use-sod/

If you need an immediate solution, you have no choice but to go with sod at this point in the season as grass seed will not germinate well in the hot, dry summer months.  If you decide to wait for the early fall to re-seed, consider choosing a grass seed mix with a higher percentage of perennial rye grass (Lolium repens) or just add additional perennial rye grass seed to your current mix.  Perennial rye grass germinates quickly and will provide the shade that will help to suppress germination of weeds.  In the spring, overseeding with white clover (Trifolium repens) in addition to your regular grass seed mix will have a similar effect.  I’m a fan of white clover but not everyone likes its appearance in their lawn.

Which ever method you choose, you may not be able to eradicate the crab grass but you can certainly get it under control.  Once the infestation is dealt with, new crab grass seedlings are easy to identify and it has a shallow root system which makes it easy to hand pull.

turf.msu.edu/crabgrass-control-in-home-lawn