Every spring as I drive about Elkhart County, I cringe upon seeing the yearly attempt to cut back ornamental grass clumps. Believe it or not, there is a proper and improper way to whack that grass down and many commercial and home landscapers alike make the same mistakes.
There are several ways to classify ornamental grasses. One way is by its period of most active growth. Cool seasons grasses like fescue and blue oat grass grow actively in temperatures between 60 to 75 degrees Fahrenheit. Conversely, warm season grasses like switchgrass, fountain grass and miscanthus grass. These species prefer temperature much warm in the range of 80 to 95.
Growth habit is another way to group ornamental grasses. Grasses either spread via underground rhizomes like Japanese bloodgrass spreading like a groundcover, or they keep well to themselves as tight bunches, slower to expand.
Every spring I see the inevitable same problem no matter what type of grass being grown, the height grasses are cut. Too many gardeners and landscapers cut grass stalks well above what is best. The worst cut grasses a foot or more off the ground rather than an inch or two. Why does it matter? It all has to do with how grasses grow. Grasses are not dumb being designed to push new growth where the most light is available (i.e. the outside edge of the bunch). Over time, the bunch expands outward while the center dies out due to a lack of light in overcrowded conditions like people moving from town centers to the burbs. The result is a spare hollow looking grass clump come summer and fall. The sooner the center dies out the sooner one must dig up and divide the clump to maintain a nice neat, tight form appropriate for most small garden beds.
Be warned, however cutting the grass clump low to the ground is not for the faint of heart. Some of these grasses put up a stiff resistance. Would you want a buzz cut when it is cold? The right tools and approach make the job much easier I find. First, a hedge trimmer with sufficient power or a good sharp rice knife or other sythe is important. Second, the right approach does wonders. Do not try to tackle the whole thing at once. Some people tie up the clump to ease handling all the stems. Cut the grass back in a series of successively lower cuts until the desired height is achieved. The third and last important step is to clear as much of the resulting debris and old dead material allowing for max sun light penetration to the new growing tissue. One can accomplish this by either vigorously brushing the clump with a stiff tined leaf rake or burning the newly cut clump (warm season grasses only).
Spring care of spreading grasses is similar with the addes step of reducing the size of the patch with an edging shovel if it is escaping the bound you have set. Different edging barriers may assist with this control providing they are placed deep enough.