The Science of Mowing
Mowing
Mowing is the most important cultural practice performed on your lawn. It has a critical impact on the quality of your lawn, even more so than fertilization and irrigation. It’s not a coincidence that our best lawns are very well mowed. The height and quality of the cut are usually excellent. To better understand this, let’s take a look at how grass responds to mowing.
Effects of mowing on turfgrass
Grass is unusual in that the growing point is not at the top of the plant. It is in the crown of the plant, which is just above ground level. This allows it to be excellent forage for animals to graze on without killing it. At least that’s the role the ancestors of today’s improved turf grass varieties played. It’s this characteristic that makes grass such an excellent landscape plant. It can be cut to various heights without damage to the growing point.
Mowing causes a slight amount of damage to the plant each time that it’s done. Each cut removes a portion of the food producing grass blades. The plant experiences a little shock, (or stress) each time it’s cut. A jagged cut will expose more of an open wound to disease, insects, and environmental stress than will a smooth, sharp one.
The plant will seal off this wound and continue to grow as long as the weather permits. If the cut has been made into the crown (way too short for the grass type) the plant will go into severe stress and may even die off. This is especially true during periods of hot weather.
Different grass types will tolerate different mowing heights. For example, golf course greens which, in this area, consist of some type of creeping bentgrass, will tolerate mowing to about 1/32.” Even then, this short mowing height is tolerated only with very intense management designed specifically for greens. Kentucky bluegrass, perennial ryegrass, and fine fescue are the predominant grass types in most home lawns in our area. They will perform best at higher mowing heights.
Research has proven that mowing height has a direct effect on root development. The higher the cut, on a consistent basis, the more extensive the root system. This results in a more vigorous plant. This stands to reason, since the blade is the primary source of food production for the rest of the plant.
General rules for mowing:
Most home lawns in our area consist of the three grass types mentioned above. They are Kentucky bluegrass, perennial ryegrass, and fine fescue. There are commonly patches of bentgrass and/or coarse fescue, but we’ll primarily be dealing with “the big three” most of the time.
There are several “rules of thumb” to follow:
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Our best lawns are those that are mowed properly on a consistent basis. Your lawn should be mowed to anywhere from 2 ½ - 3 ½ “, depending on the growing conditions. During the spring, when it’s growing quickly, you might want to cut it on the shorter end of this range. As the weather heats up, increase the height of cut. Not only does the higher cut promote greater drought resistance, it also helps to crowd out weeds, such as crabgrass, which would otherwise thrive in more open soil.
If you mow your own lawn, it’s easy to check for proper mowing. Take a ruler, stick it down to the surface and see how high it is after it’s cut. DO NOT rely on the numbers stamped on the mowing deck! These are helpful guidelines but are not always accurate.
If you have a professional mowing service, check their cut. Most reputable companies will already be mowing to the proper height for the season. However, if it’s too short, let them know so that they can make the necessary adjustments.
The final cut of the year should be down to 2” with the clippings and leaves removed. This is to prevent the dormant grass from matting down and creating favorable conditions for snow molds and winter kill. Don’t cut any lower because scalping it will expose the crown to cold air and may also cause damage.
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Mow often enough so that you don’t cut off more than 1/3 of the grass blade. This helps to reduce the shock to the plant. This may mean mowing every 5 days in the spring, which may not be practical if you’re on a 7-day schedule. It’s not as important in the spring as it is in the summer, when the lawn is under heat, and possibly drought, stress. This should be easy to follow, because growth slows down significantly. It is best to maintain a regular mowing schedule during the summer, even if it’s not growing too fast. The exception to this is if the lawn goes totally dormant. Mowing is unnecessary and may even cause permanent damage just from the wheel marks.
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Sharp blades make a cleaner cut than dull ones. If you see a whitish tinge to your lawn after it’s cut, take a close look at the grass blades. You may see ripped strands at the tips which quickly dry out and turn tan. You should see a straight cut, with minimal tan marks at the tip.
Check your mower blades periodically. They should have a consistent, smooth, sharp edge. If there are too many gouges that sharpening can’t remove, then it’s time for new blades. The edge doesn’t need to be razor sharp, but it should be able to scrape a little of your fingernail when scraped across it.
It’s best to keep an extra set of sharp blades handy. Just remove the dull blades and you have time to either sharpen them yourself or bring them to your dealer without missing a cut.
It’s hard to say how long your blades will stay sharp. This depends on your grass types, how often you mow, your cutting speed, etc.
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Clippings contain nutrients and will add organic matter to your soil. Research has shown that leaving clippings for the season is like an extra feeding of fertilizer.
If the lawn is cut so that the clippings are no longer than an inch, they will not be noticeable a few hours after mowing.
If clippings are too long, as can be the case in the spring, then it’s best to either pick them up or to double-cut the lawn. Clumps of clippings are not only unsightly; they smother the grass and may stimulate any diseases that may be present. If there is an active disease problem, then it may be wise to remove them to help prevent aggravating the condition.
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Try to mow in the morning or early evening, if possible. This will reduce the stress on the grass from the summer heat. Mowing too early will clog the mower with wet grass, unless you have a powerful commercial mower, so be sure not to mow too soon after watering, or with heavy dew.
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This will help keep your mower running efficiently. It will also help to control the spread of disease.
Usually a good scraping of the deck and washing with water will be sufficient. In case of severe disease problems, you might want to use a 10% bleach solution sprayed on all parts in contact with the grass. This will kill any spores that have been picked up while mowing.
Common mowing mistakes:
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This can kill a lawn. Every year we hear of someone mowing too short during the summer because they’ll be gone for two weeks and don’t want it to be too long when they return. This usually coincides with the hottest weeks of the year. Upon their return they find a nice shade of tan over their once-green lawn. In some instances, this is enough to kill, or at least seriously injure, the sunniest sections of the lawn. This may even happen with automatic irrigation.
It is far better to have to cut down a tall lawn than revive a brown one. If this happens, you should cut to the highest height, then gradually drop it down to normal over the course of a few weeks.
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If you’re seeing the grass blades being ripped instead of being cut cleanly, and your blades are sharp, chances are your ground speed is too fast. A rotary mower is designed to work best when the mower deck is moved up to a certain speed. If you go too fast, the blade will pull at the grass as it’s cutting, thereby causing the ripped effect. Slow down for best results.
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This happens more often on riding mowers than walk-behinds. The added weight of the driver causes a tilt when cornering, which may result the deck to tilt, even with a “floating” deck. This may be from underinflated tires, which is quite common after sitting all winter. Either have your mower serviced annually, or be sure to check tire pressure, tightness of all nuts & bolts, and be sure the deck is not tilted before using.
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If you consistently cut off too much, the lawn will have a yellowed look to it after the cut, which may take several days to disappear. This is especially true during the late spring and summer months, when hot weather and/or fungus activity is high. The portion of the grass plant that is suddenly exposed to the sun from the cut may have been harboring a disease. This will almost immediately dry out and produce an unsightly lawn. This is especially true with “red thread” fungus, which usually attacks lawns in late spring/early summer.
Hiring a professional mowing service:
If you’re contemplating hiring a professional, here’s a partial checklist to help qualify them:
Do they mow at the right height?
Most pros do a nice job. They’re usually mow at 2 – 2 ½ “in the spring, and increase to 3 – 3 ½ “in the summer.
How often will they mow?
Typically, it’ll be done once a week, and usually on the same day. This is usually when they do all the lawns in the neighborhood. This is most efficient and cost effective for them, and will consequently get you their best price. Expect a higher price if you ask for a different day on a regular basis.
Rain delays should be a maximum of 2 days, unless we get several days of heavy rain.
Because they mow once a week, they may end up cutting more than 1/3 of the leaf blade each time, especially in the spring, when conditions call for mowing more frequently. This is OK, since the weather is still cool and the grass can take it. They’ll bag to eliminate clumps.
If the lawn goes dormant in the summer, some will go to a 10-day interval. If the lawn is irrigated it should be kept on a weekly schedule all season.
Do they bag or leave clippings?
A good company will do whatever you want, and charge accordingly. We’ve found that most will bag the clippings in the spring and fall, then leave them in the summer.
Bear in mind that leaving the clippings makes less work for the mower, since there’s no disposal. However, it takes more time and effort to keep the clippings off beds, walkways, and anywhere else you don’t want them when they’re not bagging. Some mowers will even “double cut” to further cut up long clippings.
How often are the blades sharpened?
The blades should be checked every day.
How often are the machines cleaned?
This is an important question if you have a history of disease problems. A good company will work with you on this.
