My son's flower and shrub garden is heavily invaded by crabgrass. We sprayed weed killer and put down landscaping fabric and mulch before making the garden. What can we do?
Here are some links that will help you.
Crabgrass is tough to treat when it is in the flower bed.
Using herbicides will kill the crabgrass, but also anything else it touches.
Remove as much as you can this fall, this will help reduce the seeding in the spring.
You can get the problem under control by weeding by hand, it just is more work and takes time.
Here are a couple of links for you with more information.