step 1: Identify the Weeds
In most ground covers, one weed or just a few weeds cause all the problems. Take a sample to a garden center. Ask an experienced nursery person to identify it for you and tell you whether it’s an annual or perennial weed. If it’s an annual weed, you need to know when the seeds sprout.
step 2: Stop Annual Weeds Before they Start
The best way to deal with annual weeds like chickweed or annual bluegrass is to keep their seeds from sprouting. Find out when your weed is going to germinate, and spread garden weed preventer on the groundcover a week before that date. Garden weed preventer kills seeds as they germinate, but does not harm already-growing plants. Follow the package directions closely to be sure to get all the weeds.
step 3: Kill Grassy Weeds
Grassy weeds growing in ground covers can be killed with grass killer for landscapes. This herbicide kills grass without killing broadleaf plants. Spray the weeds directly with Grass-B-Gon. In about 2 weeks, they will begin to turn yellow and die. Wait 3 weeks so you can clearly see which weeds have been killed, then go over the ground cover again, spraying any weeds you missed the first time.
step 4: Kill Perennial Weeds
Perennial broadleaf weeds are the most difficult to kill because the groundcover is a perennial broadleaf plant also. Most perennial weeds have deep root systems, so cannot be successfully dug up; pieces of root left in the soil will sprout again. Kill them with Roundup, used with a shield. The shield can be a piece of cardboard you put between the weed and groundcover plants so you can spray the weed without wetting the ground cover.
A very effective shield can be made from a piece of heavy paper, lightweight aluminum sheeting, or a flexible sheet of plastic cut into a disk about 3 feet in diameter. Cut a hole in the center large enough to insert a spray nozzle and cut a slit from the hole to an edge. Bend the disk into a cone. You can adjust the size of the cone by overlapping the slit edge. Make the cone the right size for each weed, set it over the weed, and spray Roundup through the hole in the top.
step 5: Strengthen the Ground Cover
To keep the weeds from returning, help the ground cover grow thick and dense enough to keep them out. Improve the soil if necessary, then plant new groundcovers in the bare spots. Feed the ground cover regularly, water it during dry periods, and keep weeds from starting in bare spots with garden weed preventer.