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Mowing

The simple, everyday task of mowing your yard is commonly overlooked in terms of its importance to the overall health of the lawn. If done correctly, mowing will not only make a lawn look nice, but will keep it healthy and more resistant to stress and invasion from weeds, insects and diseases.

Although there are differences in optimal mowing heights among different types of grasses, for most home lawn situations, a mowing height of 3 inches is a good target. Some grasses can tolerate lower mowing heights, such as perennial ryegrass and Kentucky bluegrass, but mowing too low decrease root growth and makes the lawn more susceptible to drought and heat stress as well as increases the incidence of weeds and diseases. Never mow your lawn lower than 2 inches.

cultural intensity spectrum - mowing heights

Lower mowing heights require higher management inputs. Higher mowing heights encourage deeper roots. (Photo courtesy: A.J. Koski, Colorado State University)

Some people recommend lowering the mowing height in the spring and again in the fall, but this is not absolutely necessary. It is more important to maintain the proper mowing height and to mow frequently. Continue mowing late into the fall until the grass has stopped growing, sometimes as late as late November. This will remove excess debris and decrease the chance of snow mold. Raising the mowing height in the summer is a good practice. This higher mowing height, encourages deeper root growth and increases the lawn’s resistance to drought stress. Even a 1/4 inch adjustment (one wheel notch on most rotary mowers) will make a big difference in the health of the grass.

Check your owner’s manual for the correct height setting or place the mower on a flat surface and use a short ruler to check the distance between the mower blade and the ground. BE SURE MOWER IS OFF AND DISCONNECT THE SPARK PLUG WHEN MAKING ANY ADJUSTMENTS AND WHEN CHECKING BLADE HEIGHT.

The rule to use for determining how often to mow is the 1/3 rule which states: Never remove more than 1/3 of the leaf blade height at any one mowing. So, if your mower is set at 3 inches, you should mow when your grass reaches 4.5 inches. Violating this rule not only scalps the grass and makes it look unsightly, but also puts the grass under stress. If you just can’t seem to keep up with the growth of the grass, try raising the height a notch and slowly lowering the mowing height over time to get back at the desired height.

Contrary to popular belief, grass clippings are not a major contributor to thatch. Grass clippings are composed primarily of water and breakdown fairly rapidly in the soil. As long as you are following the 1/3-rule, the clippings will not accumulate on the lawn and should filter back into the lawn. If you are not mowing frequently enough, large clumps of clippings on the surface should be removed because they will decompose slowly and may smother the grass. A hint in dealing with excess clippings is to let the clumps of grass dry for an hour or two and mow them again. This will help break up the clippings into smaller pieces and distribute them more evenly over the lawn.

For additional information on grass clippings and their management see the University of Idaho’s publication: Don’t Bag It! Recycle Your Grass Clippings (CIS 1016)

Rotary mowers are the most common mower for homeowners. It is important to keep the mower blade sharp so the grass blades are cut cleanly. Too often this is overlooked causing the blades to tear and rip instead of being smoothly cut off. Ripping leaves blades open to diseases and stunts the grass. Sharpen the mower blade approximately every 4-6 weeks depending on the size of your lawn. If sharpening the blade yourself, use a file and follow the original bevel of the cutting edge, moving the file towards the cutting edge. Test the blade for balance by placing a screwdriver through the center hole checking to be sure the blade remains horizontal. If not, you may need to remove metal from the non-cutting edge of heavier side until balance is reached.

Reel mowers are not as common and cut grass blades with a scissors-type action. These types of mowers are much more difficult to sharpen at home. Additionally, it is important that the stationary bedknife be properly adjusted to the cutting reel for a proper cut. Check with a hardware store or lawn mower mechanic for proper adjustment and sharpening of reel mowers.

There is a little nip in the air, indicating the approach of fall. This means its time to begin winter preparations for your yard and garden. In this process, the lawn sometimes gets ignored because it stops growing and seems to present few demands. However, fall is a key time of the year in lawn growth, and you can have a definite impact on how it looks next spring if you take time to complete a few simple tasks.

Cleaning up leaves is more than making the lawn look nice. If left on the ground during the winter, leaves become wet, mat down, and smother the grass during the winter. Grass does not completely stop growing, even in the dead of winter. As it grows, grass needs to breath and matted down leaves reduces air flow. Leaves also cause quite a bit of shading during the fall and early winter before snowfall when the grass is trying to store up energy. Just as chipmunks store food underground for the winter, grass uses sunlight to make food, which it stores in its stems growing underground. If you have just a few leaves and a mulching mower, mulching the leaves and letting them filter into the grass is fine as long as they are not too thick.

Speaking of mowing, it is a good idea to continue mowing your lawn well into October and maybe even into November. These late mowings will not only help chop up any leaves you may have missed, but more importantly, will help prevent winter diseases. You may have heard the advice to lower the mowing height a notch or two on your last mowing. This can help alleviate disease, but be careful not to overdo it. You are better off to leave the mowing height the same, but mow more often into late fall instead.

Fertilizing during late fall also is a good idea since the grass, as we mentioned above, is still growing underground, even though leaf growth has slowed considerably or stopped. Since the underground part of grass is what allows it to make it through the cold winter and green up in the spring, a light late fall application is a good idea. Again, be careful not to overdo it. Apply no more than 1 lb of nitrogen (N) per 1000 ft2.

If you have an automatic irrigation system and have not touched the timer since the summer months, now is the time to do so. Grass uses much less water in the fall than during the heat of the summer, less than half as much. That means you may need to irrigate your lawn only about every 10 days depending on soil type. Depending on your location, you may want to irrigate your lawn until the end of October or even into the second week of November. In colder areas of Idaho, freezing temperatures may dictate stopping irrigation before the end of October. A final deep watering just before you winterize your irrigation system is a good idea. This will help prevent winter desiccation damage to your lawn especially if we have a winter without much snow cover.

What about controlling those troublesome perennial weeds like dandelions? Fall is the best time to kill them. As with the grass, perennial weeds are preparing for winter and sending food reserves underground. Applying herbicide around the time of the first fall frost will be most effective.

Following these year-end practices will help to ensure winter survival and improve the lawn’s appearance next year.

University of Idaho Extension

Physical Address:
E. J. Iddings Agricultural Science Laboratory, Room 52
606 S Rayburn St.
Moscow, ID

Mailing Address:
University of Idaho Extension
875 Perimeter Drive MS 2338
Moscow, ID 83844-2338

Phone: 208-885-5883

Fax: 208-885-6654

Email: extension@uidaho.edu

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Barbara Petty