OLATHE, Kan. -- In “The Slacker’s Guide to a Great Lawn,” the May 2012 Consumer Reports (CR) has good tips on how homeowners can save hours of yard work, according to a K-State Research and Extension scientist.
“The article is misleading, though, in the section that advises homeowners to ignore the one-third rule when mowing. It simply doesn’t address some important points that make the one-third rule the better choice,” added Rodney St. John, turfgrass specialist stationed at K-State’s Olathe horticulture center.
Ignoring the rule can diminish both lawn quality and environmental benefits, he explained.
The one-third rule states that turf caretakers should never remove more than a third of grass blades’ height – i.e., the plants’ leafy green tissue -- in a single mowing.
The CR article quotes a university scientist as saying the inspiration for this rule was 1950s U.S. Department of Agriculture research into using Kentucky bluegrass as a cattle forage. At that time, cutting the study grass by a third had led to the most rapid leaf production (i.e., thick regrowth).
The CR article goes on to say, however, that the rule’s landscape uses are now coming under scrutiny. The article suggests most lawn grasses can thrive after losing half or more of their leaf tissue. It implies lawn owners also can let their turf exceed traditional height-range recommendations.
“That really made me blink -- just dismissing the 60 years of research that’s built up since the USDA study,” St. John said. “Yes, strictly speaking, removing more than a third of turf height probably won’t cause too much harm, in terms of individual plant health. But, there’s more to a lawn than a single plant.”
The K-State scientist said the major reasons for mowing with the one-third rule come down to: 1) grass plant stress and lateral spread and 2) environmental sustainability.
Big Stress = ‘Skinny’ Turf
A basic in terms of horticultural health is that cutting off the top of a plant creates stress. The more tissue the plant loses, the greater its stress, St. John said.
That can be a real problem if an ice storm takes out the top half of an oak tree. If kept within certain limits, though, it can be a boost for forsythia shrubs and garden mums -- which respond to being pinched back or pruned with new and often bushier regrowth.
“Years of research have shown lawn turfs can easily handle the stress of losing up to a third of their height,” St. John said. “They also will fight back in ways that benefit your lawn.
“But, severe cuts can make turf plants vulnerable – to drought, heat, weeds, pests. It’s a direct result of how the plants tend to respond. The greater the mowing stress, the more energy turf plants will devote to getting tall again. And, that’s not what you want.”
Kansans’ favorite tall fescue and Kentucky bluegrass turfs are prime examples, he said. Tall fescue’s response to severe cuts is to look more and more like the bunch grass it is. Bluegrass curtails daughter-plant production. Both take on a thinner and more spindly appearance. The fescue may seem coarser, too.
“In contrast, following the one-third rule stimulates lateral growth. It encourages turf plants to spread out sideways, rather than expend all of their energy growing up-up-up into the air,” St. John said. “That lateral growth is what gives you a thick, dense lawn that looks beautiful, is comfortable for walking and play, and allows less room for weeds.”
Bagged Clippings = Nutrient Loss
The turf specialist is equally concerned about the clippings the CR article’s mowing advice could create.
“Long clippings aren’t easily mulched or dispersed back into the yard,” St. John said. “So, mowing them off can remind you of cutting hay. You get all these clumps of cut grass that dry out on top of your lawn.
“If they’re big enough, the clumps can actually smother and kill turf in spots. Even if they aren’t, they’re ugly enough that you’ll probably end up raking them off.”
With the one-third rule, clippings are small enough that they easily filter into the lawn, he said. They won’t add to thatch, but will recycle their nutrients and reduce lawn fertilizer needs by 25 to 33 percent.
“It’s the most efficient way available to make use of this natural resource,” St. John said. “Of course, you can add clippings to a compost pile, but most homeowners don’t compost. If they have to bag or to rake and bag, they’ll trash those clippings almost every time.
“Unfortunately, landfill space is finite. Cities such as Olathe are collecting yard waste and turning it into compost for residents. Cities such as Wichita have already considered banning the disposal of all yard waste, and I suspect that’s a sign of the times. Yard waste makes up a significant part of what we throw away. But, clippings, at least, are amazingly easy to recycle in our own yard – if we just follow the one-third rule.”