This article was posted by Rodney State John via the Kansas State University turfgrass blog-
I’ve been getting a few questions about a article in the recent Consumer Reports magazine. The article was written to help homeowners save time and reduce their workload in maintaining their landscape. The article had some good tips. But I need to clarify one of the tips that was presented regarding the 1/3 rule of mowing. Just to remind you of what the 1/3 rule is. It states that you should never remove more than 1/3 of the leaf tissue when you mow. I’ll explain more about the benefits of the 1/3 rule below. One of the important facts of the 1/3 rules is that during some of the rapid growing times of the year, like the spring and fall for cool season grasses, you may need to mow every 4-5 days instead of just once a week. But it also means during the slower growing times like July and August, unirrigated tall fescue/Kentucky bluegrass lawns may not need to be mowed but every 9-14 days.

When mowing, only remove 1/3 of the leaf tissue. Which means for tall fescue that you want to maintain at 3.5 inches high, never let it grow higher than 4.6″ before you mow it.
So the article was written to save people time in maintaining their yard. Consumer reports quoted a well know turf scientist as saying, “Most domestic grasses can thrive with 50% or more of the blade removed.” The article went on to state that ‘you can let the lawn grow to about 5 1/2 inches before mowing. …it will reduce mowing frequency by about 25 percent…. Hours saved annually: up to 10.’ I think these statements made by the turf researcher and Consumer Reports are incorrect and misleading. I’ll explain where the problem is below.
Why do we recommend the 1/3 rule?
There are several reasons for following the one third rule, but the most important are: 1. Health of the grass plant and lateral spread, and 2. Clipping management and Environmental sustainability.
Health of the Grass Plant:
The researcher states that the plant will tolerate mowings that remove 50% or more of the leaf blade without undue harm to the plant. In the article he says, “(the 1/3 rule) was inspired by research conducted in the 1950′s by scientists at the U.S. Department of Agriculture who were evaluating Kentucky bluegrass as a forage grass. If you are feeding cows, the 1/3 rule will give you the most rapid leaf production. But if your goal is a good-looking lawn, we’re now saying it is OK to take more off.” I agree that strictly speaking from the health-of-the-lawn perspective, removing more than 1/3 of the leaf blade would probably not cause too much harm to the individual grass plant. But there is more to the lawn than just one plant. Frequent mowing that comes by following the 1/3 rule stimulates lateral growth (sideways, across the lawn), and that is the type of growth we want. We want the grass to spend it’s energy and time spreading out across the lawn, not spend all of it’s energy growing up in to the air. This will create a thick, dense lawn that will look beautiful, be comfortable to walk and play on, and reduce weed populations. So if we take the turf researcher’s recommendation and remove 50% or more of the leaf blade each time we mow, the grass will be growing tall and not necessarily spreading out, possibly reducing the density of the lawn. So we want to continue to follow the 1/3 rule to make sure we are mowing frequently enough at the right height to insure that the lawn continues to spread out and stay thick, rather than grow tall and spindly.
Clipping Management and Environmental Sustainability:
The second and equally important reason for following the 1/3 rule is clipping management. Most people bag their lawns, because they are not following the 1/3 rule and they leave large, unsightly clumps of grass on the yard. So they bag it, to prevent the piles of grass from disrupting the appearance of the lawn and to prevent the piles of grass from accumulating that can actually smother and kill the lawn in spots. But by following the 1/3 rule, the clippings are cut small enough that they can be easily distributed across the lawn with a side discharge or with a mulching mower. So if you took the Consumer Report’s advice and decided to start letting the grass grow to 5.5 inches or more before you mow, odds are that the clippings will not be easily dispersed back into the lawn, and you will have to bag it. I haven’t evaluated every lawnmower out there, I suppose some mowers can successfully mulch that much grass without having to bag it, but most homeowners buy inexpensive mowers that are not the best mulchers and the homeowner will still end up bagging to prevent clumps of cut grass laying on the lawn. .
I can’t stress it enough. Don’t BAG. First and foremost, those clippings contain nutrients and by recycling those nutrients back into the lawn you can reduce your fertilizer needs by 25-33%. Secondly, in some city’s those clippings end up in the landfill. Landfill space is becoming smaller and smaller and we don’t need to be adding grass clippings to the landfill when they can be recycled back into the yard. Now, some city’s like Olathe, will collect the yard waste and compost it for their residents, and some people compost their plant material on their own property. In those instances, removing the clippings isn’t so bad, but it is still a lot of time and work and it will increase the amount of fertilizer you need to apply to your yard. So keep the clippings on your yard as much as possible.
The article also stated ‘You should also bag clippings during a lawn-disease outbreak, in which case they might need to be taken to the landfill instead of being added to your compost pile.’ This statement is not true for almost all lawns in Kansas and Missouri. The fungal diseases that attack tall fescue and Kentucky bluegrass are predominately Brown Patch and Dollar Spot, respectively. The organisms for these diseases are already in your soil, and collecting the clippings will not greatly reduce the severity or the spread of these diseases. The only time I’d be concerned about collecting and composting clippings is if you are applying pesticides. Read and follow the label. Most pesticides have a statement that says the clippings should not be collected for compost until 30 days have past, but some products have much longer wait times. Read the label of your product to be sure. Or just don’t bag. (Do you see a trend here?)
So Follow the 1/3 rule and don’t bag your clippings.
With that being said….
I do know that there are times like when you go on vacation, or it is raining and raining and you can’t get out in the yard and mow frequently enough. Think of the 1/3 rule and don’t bag rule as ‘guidelines.’ Try to following it as much as you can, but don’t loose sleep about it when mother nature or outside forces prevent you from mowing often enough. Usually what I recommend in those situations where the lawn has gotten away from you and is really shaggy is one of two choices: 1. Mow it and bag it and then get back to following the rules. OR 2. Mow it 2 or three times. First, raise the mower as high as it will go and mow it and mulch or side discharge the clippings back into the yard. Then lower the mower a notch or back to your original setting and mow the yard again, either that same day or the next day. Mow and repeat if necessary until you get back to your recommended height. And then get back to following the rules.
For more information about proper mowing or proper care and maintenance of the grasses in your lawn, check out the Publications Section over at KSUTurf.com. Homeowners can also get more help from their local extension office.

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