Turfgrass Response to Mowing Pt. 2

Recently, we discussed the impacts mowing can have on your grass. While it is necessary for a well-maintained lawn, we must consider its impact. A key question is... what length should I keep my grass?

The lower you maintain your grass, the higher the maintenance requirements. Shorter roots of low maintained grass are affected more rapidly by high heat. Low maintained grass must be mowed more often than higher maintained grass. Using the one-third rule, never remove more than one-third of the grass at a time.

How Much Blade Length Should Be Cut at a Time

The general rule for mowing is to never remove more than one-third of the total blade length at a time. To remove more causes more stress on the plant.

For example, if you are maintaining your Bermudagrass lawn at 1.5", you will be cutting the grass again when it puts on only half an inch of growth. If your Bermudagrass is maintained at 1-inch, then only one-third of an inch of growth puts you back on the mower. When the grass is actively growing the mowing frequency may be every few days for grass maintained at 1-inch or every week for higher maintained grass. Compare this to golf greens which are mowed daily.

What about pastures or low maintenance fields? Since you may be only cutting the grass as hay on pastures and then letting it grow back to its longest reach before cutting again, the grass will remain the same thickness.

Why the One-Third Rule

The goal is to do the least amount of harm. Removing only a third of the grass blade at a time helps keep all the functions of the plant operating efficiently. If you maintain your grass at 2-inches but wait until it reaches 5-inches before mowing, you are removing well over half the blade. Remember, the first inch of grass above the soil surface is the crown identified as white in color. From the crown, grass blades grow upward and roots grow down into the soil. The action of cutting off too much tissue shocks the grass and this occurs at the expense of the roots. Root growth may stop all growth for a considerable time if too much of the blade is cut. If a drought sets in or a heat wave, your grass may suffer.

I used to maintain my father-in-law's grass for him. He would always insist that I mow it very low so it will take longer to grow back so less mowing is required. I am sure his intention was for me to do less work. I would tell him it is not healthy for the grass and I would just mow it more often. I have found over the years that many people think the same way. If this is your habit of mowing, what is happening is the grass puts all its energy into regrowing long blades and it never thickens. You eventually end up with a very weedy lawn and your grass is of very poor quality.

Meaning of Scalping

Most people consider scalping as cutting too low exposing the white color of the grass crown. Most of the time the grass will recover, but may suffer if this is repeated too often. The definition of scalping is not only removing grass to the soil level, but includes removing too much tissue that causes an undesirable effect. An example is removing 4" of grass blade length to bring it back to a 2" height in a single cutting. This can still be considered scalping. As stated, it can shock the grass and force it to use stored nutrients to recover. The grass must then be forced to produce enough carbohydrates through photosynthesis alone to keep up with daily functions since its reserves may be partially depleted.

How to Mow Overgrown Grass

If your goal is to take over-grown grass and bring it back to the proper height, this is one way to do it. Start by only cutting off a third of the blade length at a time. Wait for a few days and cut again only removing a third at a time until it reaches the desired height. In between mowings make sure you are irrigating as needed and paying close attention to the appearance of the grass. If there is a problem then halt the mowing until you investigate the cause. You should make sure your blades are sharp to shorten the healing time.

This idea of watching grass appearance is important. Most turf managers who regularly maintain at lower heights know grass is more stressed than higher maintained grass. The grass appearance after mowing, along with the grass color, weather, moisture and other factors affect the grass more quickly. The lowest maintained grass, which are golf greens for example, have short roots that can overheat so heat is a concern. The grass temperature is often taken (literally) and syringing with water is often performed to keep it cool. Diseases are more common on lower maintained grass. Daily mowing, heat stress, spoon feeding nutrients and disease occurrence are some reasons why Bentgrass is considered such a high maintenance grass.

Exceptions to the Rule

Perennial Ryegrass: P. Ryegrass has proven to be, in some regards, an amazing grass. As a stand alone grass, its primary range is in the Transition Zone. But, it is the best grass in the south for growing in dormant Bermudagrass and on Bermudagrass golf greens.

You may be wondering how Perennial Ryegrass can be used on golf greens since they are maintained so low. Bermudagrass greens, like other varieties of Bermudagrass, go dormant and turn brown in the winter. In the summer months these greens can be mowed daily at 1/4". Perennial Ryegrass that is overseeded on greens in winter can be mowed at 1/2" without harm to the grass (Dr. Nick Christians, Fundamentals of Turfgrass Management).

Researchers do not know exactly why Perennial Ryegrass survives this low mowing, but it is the only one that can be used in this way. In the spring, even lower mowing to 1/3"or 1/4" helps to remove the Perennial Ryegrass and the Bermudagrass greens take over again.

Centipede Grass: Centipede grass starts to decline if not mowed. It thrives when it is maintained at lower heights. Mowing heights are from 1" to 2" (be sure to read your variety specifications) and if maintained higher this can lead to diminished quality.

How Turf Formula® and SuperCal® Help

Turf Formula®and SuperCal® work together to make your soil better for plant growth. Aside from a natural increase in nutrients, disease pathogens are lowered. University of Missouri/Columbia found that 35% of Brown Patch Pathogens were reduced in 24-hours. Many of the soil microbes, such as protozoa, feed upon pathogenic microbes that infect plants. Pathogenic microbes can reach a threshold where disease pressure reaches the point of infection, but using Turf Formula® can help keep them under control.

This duo is sure to make a difference and improve your turf this growing year.

Russ James
AgriGro Turf Specialist

Question? Contact us.