Correct Lawn Grass Length? - Ask Extension
My husband has decided to let the lawn grow tall because dog play is tearing up the lawn. He thinks that is best to keep the grass stronger. I read ...
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Correct Lawn Grass Length? #824874
Asked April 08, 2023, 3:54 PM EDT
My husband has decided to let the lawn grow tall because dog play is tearing up the lawn. He thinks that is best to keep the grass stronger. I read from multiple sources we should keep lawn 2" to 3" and understood that the grass spreads out as it grows if it is cut regularly. My thinking is that it is the best way to keep the bald spots filling in. We aren't going for a perfect lawn. We have even introduced clover to the lawn to help with pollinators. But right now there is grass starting to fall over and I understood that the grass starts to make problems for itself when it lays down: no light, more disease. When I find info on the internet about lawns my husband discouts it because he doesn't believe it is a scientific source. That is why I am asking you.
Also, is it true that when we do cut this long grass that we can only cut off 1/3 at a time? If so what will happen to the grass if you do cut down 18" long grass with a weed-wacher to 4"? I know that is what my husband will ask next.
Multnomah County Oregon
Expert Response
Hello Debie,
Turgrass responds to consistent mowing at the correct height by getting denser. The lower and more often you mow, the denser the lawn and the finer the leaf texture becomes within a grasses' tolerance range. If you mow below a grasses' tolerance range, it will thin out and other grasses and broadleaf weeds will encroach. The mowing height range for most grasses is between 1.5 and 3 inches. In general, for most lawns 2 - 2.5 inches is optimum because if you are mowing at 3 inches, your lawn may grow to 5 or 6 inches before you mow it again. We have had problems with field mice in our trials when we do trials mowing at higher heights meaning greater than 3 inches.
Turfgrass and other plants produce food (carbohydrates) through photosynthesis. When you mow grass leaves, you reduce the grasses’ ability to produce food. The grass senses it is low on food (carbohydrates) from photosynthesis, and it puts all its energy into producing more leaves by producing more branches with more leaves. This process is called is called "tillering". So, in effect, the mowing creates the density of the grass.
If you let the grass grow taller, there is no need for the grass to tiller and your lawn thins out. The other big problem is that in our wet climate, we get a lot of fungal diseases in late fall through spring. Tall grass makes matters much worse because there is no air flow and you create a perfect micro climate for fungal diseases. If the wet grass starts falling over, the taller grass shades the grass next to it and it will die from lack of light.
The same disease problems occur in the summer if you irrigate too much or irrigate during the daytime in hot weather and you are mowing your grass too high.
As far as the one-third rule goes, in my opinion, it is a bit over blown. The history of the one-third rule goes back to a research study which found that when you removed more than 40% of the leaf tissue, you stunted root growth for a time. For simplicity of communication, the 40% got changed to 1/3.
This result makes sense because the plant is responding to losing lots of leaf area at one time by putting all its resources into producing more leaves, so it is not going to send any food to its roots for growth. This stunting of roots can be important if you are trying to produce exceptionally high quality turf (e.g., on a sports turf or a golf course) and are mowing low, but for homeowners, it is not a big deal. It is not going to kill your turf. I see homeowners every spring, who have waited too long to mow their lawns over winter, mow their lawns when it is 6 - 8 inches tall. And the lawn survived fine.
What is more of a problem when you remove too much leaf tissue (we call this scalping) is leaving the clippings on the lawn. These clumps of leaves get wet and smother the turf and will kill the grass underneath.
Your lawn is analogous to a sports field. There is a lot of traffic that is thinning the lawn. The solution is to over seed at least a couple times per year (spring and fall). Grass seed is not very expensive, and it is much cheaper (per pound) if you buy a large bag. Now is the perfect time to over seed because you do not have to irrigate every day to get the seed to germinate. I would use perennial ryegrass because it is one of the most wear tolerant grasses and it germinates quickly. You can either apply it to your entire lawn with a drop spreader (6 lbs. of seed per 1,000 sq. ft.) or hand seed the thin areas.
As far as the mowing height goes, I would not mow your lawn any higher than 3 inches. At that height, the lawn will be as robust as it can be. If the dogs destroy it, then you need to come up with a different solution other than grass.
I have seen back yards destroyed by dogs that dig holes. In these cases, a different grass or changing maintenance practices such as mowing height cannot solve the problem; the dogs will always win. You either need artificial turf, concrete, or some type of ground cover the dogs will stay away from.
I hope this helps. Good luck.
Turgrass responds to consistent mowing at the correct height by getting denser. The lower and more often you mow, the denser the lawn and the finer the leaf texture becomes within a grasses' tolerance range. If you mow below a grasses' tolerance range, it will thin out and other grasses and broadleaf weeds will encroach. The mowing height range for most grasses is between 1.5 and 3 inches. In general, for most lawns 2 - 2.5 inches is optimum because if you are mowing at 3 inches, your lawn may grow to 5 or 6 inches before you mow it again. We have had problems with field mice in our trials when we do trials mowing at higher heights meaning greater than 3 inches.
Turfgrass and other plants produce food (carbohydrates) through photosynthesis. When you mow grass leaves, you reduce the grasses’ ability to produce food. The grass senses it is low on food (carbohydrates) from photosynthesis, and it puts all its energy into producing more leaves by producing more branches with more leaves. This process is called is called "tillering". So, in effect, the mowing creates the density of the grass.
If you let the grass grow taller, there is no need for the grass to tiller and your lawn thins out. The other big problem is that in our wet climate, we get a lot of fungal diseases in late fall through spring. Tall grass makes matters much worse because there is no air flow and you create a perfect micro climate for fungal diseases. If the wet grass starts falling over, the taller grass shades the grass next to it and it will die from lack of light.
The same disease problems occur in the summer if you irrigate too much or irrigate during the daytime in hot weather and you are mowing your grass too high.
As far as the one-third rule goes, in my opinion, it is a bit over blown. The history of the one-third rule goes back to a research study which found that when you removed more than 40% of the leaf tissue, you stunted root growth for a time. For simplicity of communication, the 40% got changed to 1/3.
This result makes sense because the plant is responding to losing lots of leaf area at one time by putting all its resources into producing more leaves, so it is not going to send any food to its roots for growth. This stunting of roots can be important if you are trying to produce exceptionally high quality turf (e.g., on a sports turf or a golf course) and are mowing low, but for homeowners, it is not a big deal. It is not going to kill your turf. I see homeowners every spring, who have waited too long to mow their lawns over winter, mow their lawns when it is 6 - 8 inches tall. And the lawn survived fine.
What is more of a problem when you remove too much leaf tissue (we call this scalping) is leaving the clippings on the lawn. These clumps of leaves get wet and smother the turf and will kill the grass underneath.
Your lawn is analogous to a sports field. There is a lot of traffic that is thinning the lawn. The solution is to over seed at least a couple times per year (spring and fall). Grass seed is not very expensive, and it is much cheaper (per pound) if you buy a large bag. Now is the perfect time to over seed because you do not have to irrigate every day to get the seed to germinate. I would use perennial ryegrass because it is one of the most wear tolerant grasses and it germinates quickly. You can either apply it to your entire lawn with a drop spreader (6 lbs. of seed per 1,000 sq. ft.) or hand seed the thin areas.
As far as the mowing height goes, I would not mow your lawn any higher than 3 inches. At that height, the lawn will be as robust as it can be. If the dogs destroy it, then you need to come up with a different solution other than grass.
I have seen back yards destroyed by dogs that dig holes. In these cases, a different grass or changing maintenance practices such as mowing height cannot solve the problem; the dogs will always win. You either need artificial turf, concrete, or some type of ground cover the dogs will stay away from.
I hope this helps. Good luck.
