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Yard and Garden: Lawn Mowing

AMES, Iowa – Lawn mowing is the most time consuming practice related to lawn care – but when done properly mowing plays a vital role in maintaining a healthy, sustainable lawn. Horticulturists with Iowa State University Extension and Outreach answer lawn mowing questions; to have additional questions answered contact Hortline at hortline@iastate.edu or 515-294-3108.

When mowing the lawn, what is the proper mowing height?  

Kentucky bluegrass lawns should be mowed at a height of 2.5 to 3 inches in the spring and fall months. Mow bluegrass lawns at a height of 3 to 3.5 inches in June, July and August. A higher mowing height in summer helps to cool the crowns of the turfgrass plants, encourages deeper rooting and provides more leaf area for photosynthesis during the stressful summer months.  

Mowing below the recommended range may scalp the turf and cause the turfgrass to deteriorate. Extremely low mowing heights decrease the total leaf surface area, carbohydrate reserves and root growth, creating a situation where the turfgrass plants are unable to produce enough food to meet their needs. This makes the plants more susceptible to drought, high temperature and wear injury. In addition, the bare areas created by a decrease in turfgrass density increase the likelihood of weed problems.  

Mowing too high can also create problems. Mowing above the recommended range reduces tillering and causes matting of the grass. Reduced tillering results in fewer and coarser plants, while matted grass creates a micro-environment that encourages disease development. 

How often should I mow my lawn? 

Kentucky bluegrass lawns should be mowed at the height of 2.5 to 3 inches in spring and fall. Set the mower blade to a height of 3 to 3.5 inches during summer.  

As a general rule, never remove more than one-third of the total leaf surface at any one mowing.  For example, to maintain a lawn at 3 inches, the grass should be mowed when it reaches a height of 4.5 inches.  

Mowing frequency is based on the growth rate of the turfgrass. Weather conditions, cultural practices (such as fertilization and irrigation practices) and other factors determine the growth rate of turfgrass.  

Kentucky bluegrass and other cool-season grasses grow quickly in spring when weather conditions are favorable. The growth of cool-season grasses slows in summer and then picks up again in fall. Fertilizing and irrigating the lawn on a regular basis promote turfgrass growth. In spring it may be necessary to mow every four to five days, possibly only once every one to two weeks in summer, with more frequent mowing again in the fall. 

Should I remove the grass clippings when mowing the lawn? 

When the lawn is mowed properly, grass clippings do not need to be removed or bagged. Small clippings filter down into the turf and quickly decompose, returning essential plant nutrients to the soil. Lawn clippings do not significantly contribute to thatch development.  

Grass clippings may need to be bagged or raked and removed when mowing extremely tall grass. You may also want to bag the grass clippings and use them as a mulch in vegetable and flower gardens. 

When should I mow a newly seeded lawn? 

Mow newly seeded Kentucky bluegrass lawns at a height of 2.5 to 3 inches when the grass reaches a height of 3.5 to 4 inches.  Frequent mowing at the height of 2.5 to 3 inches encourages the grass to spread and promotes a thicker lawn. 

Is it a good idea to alternate the mowing direction when mowing the lawn? 

Alternate your mowing pattern or direction each time the lawn is mowed. Repeatedly mowing the lawn in the same direction pushes the grass over rather than cutting it cleanly. Also, different mowing patterns reduce soil compaction and wear from the mower wheels. 

Does it harm the grass to mow the lawn with a dull mower blade? 

A sharp mower blade cuts the grass. A dull blade tears the ends of the grass blades. The damaged tissue dries out, giving the turf surface a whitish appearance. Also, the torn leaf tissue loses greater amounts of water and increases the possibility of disease problems. Sharpen the mower blade at least twice a year.  
 

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PHOTO: Mowing too close results in scalping.

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