Will Roundup Kill Bar Harbor Juniper?

Bar Harbor juniper (Juniperus horizontalis "Bar Harbor") works well as a ground cover, designed to prevent erosion and provide an attractive topping to slopes or other areas where you need low-maintenance coverage in U.S. Department of Agriculture plant hardiness zones 4b through 9. It won't tolerate many herbicides that touch the foliage, including those containing Roundup's active ingredient, glyphosate.

Glyphosate works as a powerful postemergent, nonselective herbicide. This means that it kills nearly any plant it touches, usually within a day or two. It's especially helpful when you have many weeds in a small space; you can knock them out without having to dig out each individual weed by the roots. However, because it's nonselective, it can also kill your Bar Harbor juniper if you let the liquid touch the juniper foliage.

Glyphosate is a plant poison that's absorbed by the leaves. The herbicide passes into the plant's vascular system, moving throughout the plant as the plant transports nutrients to its leaves, stems and roots. It kills the plant from the inside, causing leaves to wilt and roots to shrivel. According to Roundup manufacturer Monsanto, it doesn't leach through soil, which means you can spray it around the roots of other plants, as long as you don't touch the leaves.

A problem with Bar Harbor juniper plants is their spreading ability. To serve as effective ground cover or erosion control, the plants must be located close enough to each other that the spreading branches eventually overlap. This still allows room for weeds to poke through the foliage, but it doesn't give you an easy way to spray the weeds with glyphosate without spraying the juniper foliage as well. A few drops of glyphosate might create dead spots in the green needles but allow the plant to live. Spraying an entire weed, however, could kill all the juniper needles around the weed, and the spraying could use enough of the chemical to kill the juniper plant as well. If you must use glyphosate in your Bar Harbor juniper, dip a small paintbrush in the herbicide and paint the leaves of the weed so you won't inadvertently spray the juniper.

There are other options besides glyphosate to get rid of weeds in your Bar Harbor juniper. Pulling them by hand is effective, but be sure to wear gloves to prevent skin irritation from the prickly juniper needles. Many herbicides designed to target certain weeds can harm your Bar Harbor juniper, such as those containing fenoxaprop and fluazifop, but there are a few that are marked as safe for junipers, such as bentazon. Read the labels carefully to make sure that Bar Harbor juniper is included in the list of safe plants.