How often should you mow your lawn?

Almost every answer to this question is a number of days, and almost every one of them is wrong for most of the season. Grass does not grow on a calendar. The extension guidance is better because it is expressed in the only unit the plant responds to: height.

The rule

The arithmetic works at any height. If you cut at 2.5 inches your trigger is about 3.75. If you cut at 3.5 inches your trigger is about 5.25. Pick your height, divide by two thirds, and that is when you mow.

What that means through the season

Growth rate is the variable, and it swings enormously. The interval that follows from the rule swings with it.

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When the lawn has already got away from you

It happens — a fortnight of rain, a holiday, a broken charger. The wrong response is to drop the deck and take it all off in one pass, because that breaks the one-third rule by a long way and stresses the plant exactly when it is least able to cope.

1. Raise the deck to its highest setting and cut. You will remove far less than you want to, and that is the point.
2. Wait two or three days. Let the plant recover before you ask again.
3. Drop one setting and cut again. Repeat until you are back at your normal height.
4. Deal with the clippings. Extension guidance is that clippings of an inch or less filter down and decompose quickly, but that if the lawn is wet or the grass has become too tall, clippings can mat together and smother the grass. On an overgrown cut, bag or rake.

There is an equipment consequence here worth knowing about. A deck whose maximum height is low leaves you no room to execute step one. The Greenworks LM2054 tops out at 3.6 inches; the EGO LM2135SP and Greenworks LM2108S reach 4.0.

Why frequent mowing is less work, not more

• No bagging. Clippings of an inch or less filter down to the soil surface and decompose quickly, per extension guidance. That is one fewer job and no trips to empty a bag.
• Free fertilizer. Decomposed clippings add the equivalent of one fertilizer application to the lawn each year. Bagging throws that away.
• Less battery per cut. Short growth is a lighter load, so the pack goes further and the mower spends less time near its draw ceiling.
• A better cut. A sharp blade on short growth cuts cleanly; the same blade in a hayfield tears.
• Fewer weeds over time. Extension weed guidance treats mowing height and frequency as cultural controls, because dense turf at a good height leaves less room for anything else.

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Pick the height before the frequency

Everything above depends on choosing a cutting height first, and higher is generally better on a cool-season lawn: it shades the soil, roots more deeply and needs less irrigation. Extension guidance for shaded areas goes further and recommends cutting approximately one inch higher than in sun.

Check your deck can do it. Published cut-height ranges vary: EGO publishes 1 to 4 inches over eight positions, Greenworks 1.38 to 4.0 on the 80V and 1.2 to 3.6 on the 40V, and Toro and Kobalt publish no range at all for the mowers we hold specs for.

What we cannot tell you

We cannot tell you how many days your lawn takes to grow an inch and a half. That depends on your grass species, your soil, your fertility program, your rainfall and your latitude, and any interval we printed would be wrong for most readers.

What the extension guidance gives you is better than an interval anyway: a height to maintain, a height to mow at, and a ceiling on how much to take. Measure the grass rather than the calendar.