When grass, such as the popular Kentucky bluegrass (Poa pratensis), hardy in U.S. Department of Agriculture plant hardiness zones 3 through 7, makes itself at home in the vicinity of a garden rose, such as "Peace" (Rosa "Peace"), commonly known as a hybrid tea rose and hardy in USDA zones 5 through 9, it deprives the rose of water and nutrients. In some locations Kentucky bluegrass is invasive. Recipes for homemade herbicides and grass killers are available, but they may also harm roses. Better options exist.
No Sunshine, No Grass
The easiest way to smother lawn grass around roses is to cover the grass with a layer of landscape fabric, available at garden centers. While the permeable fabric allows water and nutrients to reach the rose's roots, it prevents light from getting to the grass. This treatment will not harm rose roots. To camouflage and hold the landscape fabric in place, cover it with a layer of organic or inorganic mulch such as fine gravel. Do not allow the mulch or fabric to cover any part of the rose trunks. Leave in place for as long as possible.
A Little Extra Care for the Rose Bed
Continue with your watering and liquid fertilizer schedule without worry since these will penetrate the landscaping fabric. Hand pull any grass that sprouts in the small areas right by the rose trunks that are not covered by fabric and mulch. The fabric/mulch treatment not only kills the grass and any other weeds germinating in the rose beds, but it helps the soil retain moisture. Very occasionally tenacious grass or weeds may break through the fabric calling for parts of it be replaced. If this is necessary, make sure to overlap fabric pieces.
The Poor Man's Landscape Fabric
If the area is relatively small or the cost of fabric is too large, an alternative homemade smothering cover can be made of newspaper or cardboard topped by compost. The method is similar to the fabric treatment. Lay down a 1-inch layer of newspaper or cardboard. The latter might be obtained from flattened boxes, but ensure the boxes have not carried anything that may infect or poison the soil. Cover with several inches of mulch. The difference between newspaper/cardboard and landscape fabric is that paper and cardboard decompose much more quickly than fabric.
The best way to ensure grass, such as English ryegrass "Manhattan" (Lolum perenne "Manhattan"), hardy in USDA zones 3 through 8, does not sprout in rose beds is to prepare the beds before planting roses. This can be done by applying black plastic to the lawn area being converted to garden beds. Apply the black plastic to the turf, secure it with landscaping pins, and leave for at least one season. The black plastic retains the sun's warmth and deprives the grass of moisture and nutrients.
- National Gardening Association: Landscape Fabrics
- University of Missiouri Extension Infonet: Mulching Roses
- Missouri Botanical Garden: Plant Finder -- Poa Pratensis Group
- Missouri Botanical Garden: Plant Finder -- Rosa "Peace"
- Missouri Botanical Garden: Plant Finder -- English Ryegrass -- Lolium perenne "Manhattan"
- Photo Credit Thinkstock Images/Comstock/Getty Images