Mowing Facts

Protecting Your Investment

Mowing

Mowing is one of the most important cultural practices. Good mowing practices not only complement the visual appearance of the lawn, but also increases turf grass vigor. For proper mowing, the following five factors should be considered: height of cut, mowing frequency, disposal of clippings, mowing pattern, and type and maintenance of equipment.

Height of Cut

Mowing height is dependent on the turf species involved. The following is a table of recommended mowing heights:

COOL SEASON TURF GRASS WARM SEASON TURF GRASS
Bluegrass, Common Kentucky 2 ½ – 3 ½ inches St. Augustine 2 –3 inches
Bluegrass, Improved Kentucky (Golf Course) 1 ½ – 2 ½ inches Bermuda Grass, Common 1 ½ – 2 ½ inches
Bentgrass (Golf Course) ¾ – 1 ¼ inches Bermuda Grass, Hybrid “TIFF” ½ – 1 inches
Tall Fescue 3 – 4 inches Bahiagrass 1 ½ – 3 inches
Fine Fescue 2 – 3 inches Centipede 1 – 2 inches
Perennial Ryegrass 2 ½ – 3 ½ inches Zoisiagrass, Emerald ¾ – 1 ½ inches
Zoisiagrass, Meyer (Common) 1 – 2 inches

These cutting heights are important to maintain turf grass vigor. For instance, tall fescue mowed continually to a cutting height of 1 ½ inches will thin out, while mowing creeping bent grass above 1 inch will cause turf quality to decline and may result in disease activity.

Placing the mower on a concrete surface and measuring the height from the concrete to the bottom of the mower housing where the blade is located determine mowing heights.

If the turf is thatchy, the cutting height must be raised to compensate for the wheels sinking into the thatch or scalping will result. An example would be if thatch were ½ inch or more, rise accordingly.

To understand the basis of recommended mower practices, the physiology of grass plant must be considered. The blade of the plant is the site of photosynthesis, the process whereby carbohydrates or food is made. These carbohydrates are used for both root and shoot growth. When the leaf blade is cut, some of the area devoted to photosynthesis is removed, reducing the amount of carbohydrates available. If the amount of blade removed exceeds the recommended amount, root and shoot growth will be reduced. Shoot growth predominates over root growth when carbohydrate supply is reduced and is insufficient to support growth of both. The root system can be partially or completely lost and recovery may be slow.

Turf grass stressed by mowing too low is more prone to disease, weed invasion, drought and traffic stress. Removal of most of the blade limits food production and there is a decrease in root, rhizome, and stolen growth. This reduced growth may create thin areas in the lawn, opening the area for weed invasion. A vigorous, dense turf grass area is one of the best defenses against weed invasion. Weeds that cannot be controlled chemically may be kept to a minimum by mowing properly to encourage a thick, competitive turf. Mowing at the recommended height promotes root-shoot development and thus, a vigorous growing turf grass plant.

Mowing height should also vary with weather conditions. In late winter and early spring, mow turf grass fairly close; 2-2 ½ inches before grass growth has started. This will remove the dead or desiccated blades and help the turf grass green up faster. After grass growth has been initiated, mow at recommended heights. During periods of drought, stress, or high temperatures, raising the cutting height ½ to ¾ inches will reduce the possibility of injury by drought stress. This is especially important for cool season turf grass that may be severely stressed by high temperatures.

Location may also be a factor in determining mower height. Turf grass grown in the shade does not always receive sufficient sunlight for optimum growth. By raising the cutting height ½ to ¾ inches, the amount of sunlight received will be increased. Areas of the lawn weakened by traffic, pest injury, or environmental injury will also benefit from a raised cutting height.

Mowing Frequency

Frequency of mowing should depend on rate of grass growth and not on a time basis such as once a week. Growth rate is dependent on the turf grass species, available water and nutrient, light received, and temperatures. Optimum growth for cool season turf grass occurs from 60 – 70 degrees F, while warm season turf grass grows fastest at 80 – 95 degrees F. Cool season grasses will, therefore, grow most rapidly in the spring and fall, growth being markedly reduced during hot weather. In the spring and fall, these turf grasses may need to be mowed several times per week. In the summer, when growth is slowed, mowing may not be necessary for extended periods. If conditions are hot and dry, avoid mowing until weather conditions have changed to alleviate further stress to the plants. Drought stressed turf grass may be crushed or injured by mower wheels and foot traffic. Mowing also reduces water content due to the fact that water is lost through the top of severed blades. Unlike the cool season grasses, warm season grasses grow vigorously during the summer and need to be mowed frequently. However, in the spring and fall, their growth rate will be slowed, and therefore, the mowing frequency is decreased.

When mowing, never remove more than one third of the leaf blade at one time. For instance, if the cutting height is 2 inches, mow when the grass is 3 inches tall. Removing more than the recommended amount can disrupt root growth and “shock” the turf grass. This “shocked” turf grass is much more susceptible to insect, and disease injury. This is one of the leading causes of turf decline in the spring when leaf spot on cool season grasses is active.

It is best to mow when the turf grass is dry. Wet grass blades tend to clump and may clog the lawn mower. However, mowing should not be delayed for long periods just because the grass is wet. Long intervals between mowing usually result in the removal of more than one third of the leaf blade. Removal of the majority of the leaf blade leaves mainly shoots and stems. These plant parts are somewhat unsightly and, unlike the leaf blade, do not produce carbohydrates. A reduction in carbohydrates reduces root development and renders the turf grass more stress prone.

Clipping Disposal

Clippings allowed remaining on a lawn aid in moisture retention, insulating the soil and returning some nutrients for turf grass to use. As the clippings decompose, nutrients such as Nitrogen are returned to the soil. Research has shown that clippings do not add to thatch build up and are a valuable source of nutrients. If mowed at the correct height and frequency, clipping removal should not be necessary. Grass clippings are far more beneficial to the lawn than if they are removed and used as mulch for gardens and flowerbeds. However, if the lawn has not been mowed for an extended period of time and the clippings are excessively long and dense; they should be removed to prevent smothering of the turf grass.

Pattern of Mowing

To improve the quality of the cut and the appearance of the lawn, the mowing pattern should be considered. Mowing continually in the same direction often results in wave-like ridges that develop at right angles to the mowing pattern. To eliminate these ridges, alternate mowing direction after each consecutive mowing. This will also serve to distribute traffic and wear more evenly over the lawn. If possible, turn on the sidewalk or driveway to prevent the wheels from bruising the grass blades.

Mowing in straight lines also adds a neat, manicured appearance to a healthy lawn. When mowing relatively steep slopes, mow across the slope instead of up and down.

Types of Equipment and Mower Maintenance

There are basically two types of lawn mowers, reel and rotary, both of which have advantages and disadvantages. Rotary mowers are simple in construction, require less maintenance, and cost less than reel type mowers. Rotary mowers work by the rotation of a horizontal blade. The distance from the blade to the ground on a level surface determines cutting height. Rotaries are most often effective at cutting heights or more than one inch and can cut weeds as well as tall turf grass. Rotary mowers, unlike reel mowers, operate at high speeds and can be hazardous. Debris such as rocks or twigs can be ejected from the rotary mower and can be dangerous to the operator as well as anyone near by. When mower is running, keep hands and feet away from the blade.

To determine if your rotary blade needs sharpening, examine the ends of the grass blades. If the ends of the grass blades are shredded, it is time to sharpen the mower blade.

Shredded grass ends eventual turn brown, giving the whole lawn an overall brown appearance. Besides giving the lawn an unsightly appearance, a dull blade also causes the plant to use more water. Because they dull quickly, mower blades should be sharpened or filed once every 4 cuts. The more often you mow the more often your mower blade will need to be filed. New mower blades will also need sharpening because the blades are shipped dull for safety reasons.

The importance of a sharpened blade cannot be emphasized too strongly. Since different turf grass species vary in composition, relative ease of cutting varies. A mower used to cut “tough” turf grass will need to be sharpened more often than easily cut varieties. Tall Fescue and Zoisiagrass are both difficult to mow due to their composition and tissue structure. Bluegrass and bentgrass, unlike the two previous turf grass species, are relatively easy to cut.

To sharpen a rotary mower, stroke each cutting edge several times with a flat file. Be sure to have the mower unplugged or the spark plug wire disconnected before sharpening. Failure to take these precautions can result in loss of fingers or even a hand. If the blade is removed, be sure and replace it correctly. Putting the blade on upside down can create problems.

The speed of the mower is also important, especially for riding lawn mowers. If the mower is going too fast, the leaf blades will not be cut but only injured. The damage looks similar to dull blade injury.

A mulching mower is a different version of the rotary mower. This type of rotary cuts the leaf blades into very fine pieces and forces these pieces downward into the turf where they decompose quickly. Mulching mowers have the advantage of automatically recycling clippings back to the lawn. However, the grass must be dry and not excessively long when it is being mowed or the effectiveness of the mulch mower will be reduced. Damage to the turf can result if not mowed under proper conditions.

Special Considerations

When re-fueling your lawn mower, always have it turned off and on a paved surface. Gasoline spills spilled on the lawn can cause the turf grass to turn brown and die. Since exhaust from a lawn mower can injure turf grass, start the mower on a paved surface and never leave a running mower standing on the lawn. Brown areas in the lawn will result.

Scalping or the removal of excessive amounts of the leaf blade will result in the lawn appearing brown and stubbly. This can be caused be several factors. Failure to mow for long intervals often results in removal of large amounts of the leaf blades. If the lawn has not been mowed for a long period and the turf grass is high, raise cutting height to the highest level so that the least amount of the blade will be removed. Gradually lower the cutting height to the recommended level with successive cuttings.

Scalping can also be a problem on turf grass with excessive thatch. The lawn mower wheels can sink into the turf grass, lowering the cutting height. Uneven areas in the lawn or lawn mowers that have unleveled wheels can also result in scalping.

POINTS TO KEEP IN MIND

  • Examine the leaf blade ends to determine if the lawn mower blade needs sharpening.
  • When sharpening a blade, always unplug it or disconnect spark plug wire.
  • ALWAYS fill fuel or start mower on a paved surface.
  • Whenever operating a lawn mower, observe safety precautions.
  • NEVER remove more than 1/3 (one-third) of the leaf blade.
  • Mow turf grass at recommended height.
  • Raise cutting height in hot weather.
  • NEVER mow in the heat of the day.

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