Mowing your lawn is the most often applied cultural practice performed on grass. It is necessary for a well-maintained lawn, professional landscapes, and sports fields. A beautiful lawn with rich green grass is easy on the eyes, adds curb appeal, and is a pleasure to play on. What is not often considered is how grass responds to mowing. However, a key understanding in professional turf management is knowing that mowing is merely tolerated by grass and as a result has specific reactions to it. What this means is that mowing is followed by predictable responses in the blades and roots.
We will cover the key responses to mowing and how you can use these to your advantage.
Mowing is Always Stressful to Grass
Many people see mowing as something similar to getting a haircut – as something that causes no harm and usually looks great for a while. But, it’s actually the complete opposite with grass. Grass blades are filled with Chlorophyll that is used as the means of producing carbohydrates through photosynthesis. These carbohydrates are consumed by the plant as energy to keep all plant functions operating efficiently. Longer blades have more surface area and more chlorophyll to absorb light for photosynthesis. When grass is mowed, you are removing a portion of the blade that is necessary for photosynthesis and as a result the plant stresses. This stress triggers several different plant responses.
In addition to removing a portion of the grass blade, the blade’s cuticle (the hard, waxy surface) is cut by the mower blades creating an injury that must heal. Sharp blades create less of an injury than dull blades. The cuticle is important because it creates a barrier that protects the internal tissues of the blade.
Healthy plants have thicker, stronger cuticles that help resist certain pathogenic fungi that enter the blade via penetration through the cuticle. Mowing the grass offers a location for a pathogen to enter without having to penetrate the cuticle. Reel mowers cut like scissors and leave behind a smooth edge that heals very quickly. When you see brown and shredded grass ends, this is a sign that your blades need sharpening. These larger injuries created by dull blades heal more slowly and offer an even broader area for diseases to potentially enter.
The Good News
Don’t lose heart, however. Fortunately, of all of the different plant species, grass is among the most tolerant, especially when it comes to mowing or grazing by most animals. Grass can handle a great amount of abuse and still look good. This is due to the fact that the growing point of grass is close to the soil’s surface and the grass can easily produce additional tissue in response to mowing. Still, there are things that you can do to weaken the health of the plant and in most cases, you will want to avoid these, if possible…
Understanding How Mowing Effects Grass: Considerations Before Mowing
Before mowing, you should consider that every grass type has a “lowest mowing height recommendation.” This means if you mow lower than what is recommended for that grass variety it can start to weaken the grass, which leads to thinning and even die back.
As a standard rule in mowing, the lower the mowing height, the shorter the root growth. Taller maintained grass of the same species will have longer, farther-reaching roots than if mowed at a lower height. Why is this?
First Predictable Consequence to Mowing:
Let’s take Turf Type Tall Fescue (TTTF), for example. Mowing comes with predictable responses with this grass species. Most fescue grass turf varieties can be maintained from 1.5-inches to 4-inches. If left unmowed, most turf-type tall fescue grass will only reach up to 10″ or more in height. That is about 9-inches of blade length for photosynthesis.
However, if you maintain your grass at 2-inches, that length is not long enough for photosynthesis to meet all the plant’s needs. Therefore, in response to the low mowing, the grass will put out more tillers (stems and grass blades) that will develop below the cutting height to compensate for the loss of tissue. In this way the shorter grass will actually be thicker, having more blades to absorb sunlight to compensate for the lower mowing so it can effectively carry out the necessary photosynthesis. For this to happen you will consistently need to mow before the grass puts on another inch in height. Golf courses often utilize this because a thicker playing field is better for the ball. But this lower mowing height requires a higher level of maintenance.
Second Predictable Consequence to Mowing:
In order for the grass to produce twice as many blades due to consistent low mowing, it must redirect energy that would normally go somewhere else. For grass, it redirects from the roots. The grass redirects energy from the roots to the blades where it will consume this energy to produce even more blades. In contrast, the higher maintained fescue is somewhat less thick with the longer blade length but has a deeper and farther-reaching root system.
Note: There is a direct link between root depth and mowing height. Low mowing produces shorter roots where deep roots are a byproduct of higher maintained grass.
Using this to Your Advantage
Depending on where you live in the country, how tall you maintain your grass can be important. If you have frequent summer droughts or even long stretches of hot weather, like California, maintaining your grass at 4-inches will send down deeper roots than lower maintained grass. This root depth will help the grass survive the heat and drought. This also depends on how you follow correct irrigation methods of deep watering (at least 4-inches of moisture reaching down into the soil) followed by no irrigation until the grass shows signs of needing it again.
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