To prevent crabgrass, maintain a healthy lawn

Iseeded some bare areas in my lawn in late spring and now it seems I only see grassy-looking weeds. The leaf blades are wider and lighter green than the bluegrass in the rest of my lawn. What is this, and what can I do to get rid of it?

— Jonathon Jacobsen, Wilmette

It sounds from your description like you have a crabgrass infestation. This summer, I have seen a lot of crabgrass in home lawns. The crabgrass in one friend’s lawn choked out most of the bluegrass that was seeded in late spring, resulting in a very frustrated gardener. There may have been a crabgrass seedbank in the existing soil. Or, when my friend bought soil to use for grading, crabgrass seeds may have been mixed in with the soil. I even have some crabgrass moving into my lawn at home for the first time. This seems to be