The following excerpts are from a recent University of Missouri publication, “Raise the Deck to Make Your Turf the Trees of Your Lawn.”
Over 10 separate studies since 1958 have found a direct correlation between mowing heights below 3.5 inches for tall fescue or Kentucky bluegrass lawns and a substantial increase of weeds such as dandelion and crabgrass. Mowing too low results directly in more annual weed invasion and a reduction in the turf stand over the summer.
In quite a few ways, mowing turf grasses at a height of 3.5 to 4 inches allows a competitive advantage over weed species. Higher cut lawns will exclude sunlight, heat and space to annual weeds. The existing weed seeds in your lawn need sunlight to heat the soil surface for germination and aid young seedlings in growth. Growing tall turf robs them of this sunlight and doesn’t allow weeds to establish and compete. More importantly, tall fescue lawns are simply healthier at this height.
Try to connect the height of the turf grass with the depth of the root zone. At this time of spring, tall fescue is getting its last few weeks of luxury growth in perfect temperatures that it can use to build a dense root system. The more leaf blade the plant has now, the more sunlight it can harvest and the more food it can make for itself. When the heat of summer hits in June-August, that luxury will be long gone, and the plant will be subjected to a number of stresses including heat, drought, and disease.
Mowing frequency is also an issue. To avoid scalping at taller mowing heights or excessive clumping of clippings, mowing may need to be done every 5-7 days when tall fescue or Kentucky bluegrass is really growing during the spring. Additionally, pay attention when weed eating around roads, sidewalks, and lawn margins. The tendency is to cut these areas shorter and scalp the turf, which allows weed emergence and a “ring around the collar” appearance of weeds in a lawn.
Remember, mow your lawn often and raise your mower deck to the top notch.
Thanks to the University of Missouri for providing this helpful information!