How to Get Rid of Phlox

Mix 2 2/3 ounces of herbicide with 1 gallon of water in a spray bottle or 1 gallon garden sprayer to make a 2 percent glyphosate solution. The regular formula of common glyphosate brands contains roughly 41 percent glyphosate, but check the label before mixing. Use a product with a surfactant so the herbicide coats foliage more easily.

Use lopping shears to cut shrubs back to about 6 inches. Mow over shorter phlox with your lawn mower set at its highest setting.

Spray the phlox with the glyphosate solution to completely wet all parts of the phlox plants. The surfactant coats the plant and reduces runoff. Allow seven to 10 days for the herbicide to take effect and dry out the plants. The phlox should shrivel up and turn brown.

Spray any green parts that remain after 10 days with the herbicide. Wait until those plants die.

Turn the dead plant material into the soil, using a garden hoe or rototiller. It will improve soil tilth and drainage. The plant matter decomposes in the soil, just as plant matter breaks down when added to a compost pile. Alternatively, you can break up the soil, rake up the dead phlox and add it to your compost pile or a green materials waste bin.

Monitor the area for new phlox growth and spray the new growth immediately with the herbicide solution. Repeat this process until the phlox no longer returns.