Cutting it Close

– Christine Gelley, Agriculture and Natural Resources Educator, Noble County OSU Extension (originally published in the Ohio Farmer on-line)

We find more dead tissue in grass stands that are mowed too close. Photo by author

All of us have a bad habit here or there that we have developed over time. Bad habits are often questionable actions that can cause some stress, but rarely have direct negative consequences immediately after. Usually the negative consequences are compounded over time into large problems and that is when realize we have gone wrong.

A bad habit that many grass managers have in lawn and hay systems is cutting it too close. By “it,” I mean the grass. There are some misconceptions about what the best height is to cut grass. It can also be confusing, because ideal cutting height varies with type of grass. The common denominator is that many homeowners and haymakers are cutting the grass too low and inducing stress responses on the plants that cause us issues down the road.

Depending on grass species, variety, and environmental conditions mowing height and frequency can vary greatly. The turf grasses that grow on a professional golf course are drastically different from the turf on a children’s soccer field. The most common plants in tall grass warm-season pastures or short grass cool-season pastures are drastically different. In all cases, we want to be aware of where new growth occurs on the grass stem and how deep the root system goes.

The region on the stem where new growth emerges is called the “apical meristem”. Grasses will grow back best after a cutting if the apical meristem is not damaged. If the apical meristem is mowed off, the plant must produce a new shoot, called a “tiller”, in order to regrow. This draws additional nutrients from the root system. This is true in lawns, hay, and grazed pasture.

Find healthier, more aggressively growing plants in grass stands mowed at appropriate heights. Photo by author

If grasses are regularly mowed or grazed too short, it can easily deplete root energy reserves, causing nutrient deficiencies and low stand persistence. Low persistence makes your grass stand look patchy. Weeds soon fill in those patches. Often people get into a cycle of cutting it too close and then fertilizing, irrigating, and or applying herbicides to try to remedy the damage. In those cases, the problem is not soil fertility or water in the soil or that new weeds are suddenly invading. More likely, it is reduced ability of the plant the draw the nutrients and water from the soil. Together regular soil tests and stand evaluations can help you troubleshoot problems that arise.

A general rule for lawns is that when you mow, you should only be removing one third of the total leaf area. That means if the grass is six inches tall, mowing it to four inches, or from three inches to two inches, depending on your grass. In hay production in cool-season pastures (ex: orchardgrass, tall fescue, etc.) mow or graze before seed heads develop, down to three to five inches. In warm-season pastures (ex: switchgrass, sorghum-sudangrass, etc.) mow or graze down to 8-10 inches if you expect regrowth. (See table 1 below for species suggestions.)

The idea that the lower you mow the more grass you get is misguided. The lower you go the more stems you remove than leaves and the more soil material and rocks you kick up as you mow. That is not good for your grass, soil, or equipment. Mowing or grazing grass too low is called “scalping”. Don’t scalp anything you expect to live afterwards.

Setting your mower deck/cutterbar high enough for the grass you are managing can be a challenge for some machinery. If you cannot adjust it as high as you need, consult an implement dealer to investigate if additional components can be installed to raise the height.

Collars for cutterbar lift cylinders or high clearance skid shoes may do the job. Sometimes adjusting the cutterbar angle can increase cutting height. Getting this situated will take some trial and error. Be cautious as you mow and watch for side drift or improper trailing of the implement. When making adjustments with collars or shoes, always power off the machine, park on a level surface, and engage safety locks.

Over time, mowing at a higher height in the canopy will improve the health of your grass stand, reduce the presence of weeds, and improve the quality of your soil, giving you thicker stands of desirable grasses. To learn more about mowing heights for your lawn or hay, feel free to contact your County Extension Office or the author through email at gelley.2@osu.edu.