Americans spend $40 billion each year on lawns—but money isn’t their only contribution. The typical home owner also devotes 73 hours to yard care every year, the equivalent of nearly two full workweeks.

That massive investment of time, effort and money could go to waste if you make any of these eight common lawn mistakes…

1. Skipping a weekly mowing. This seems harmless but can cause lasting damage. Extended gaps between mowings allow lawns to grow tall and shaggy rather than thick and dense. If done repeatedly, fewer blades of grass will grow because tall grass will block out the sun. When that tall grass finally is mowed, the gaps between the blades will be large enough for weeds to take hold.

When grass is allowed to grow tall, there also is a good chance that the subsequent mowing will “scalp” the lawn. Mowing a lawn too low is not the only scalping danger—cutting off more than one-third of the height of grass in any single mowing also is very stressful and damaging to lawns.

If you let your grass grow to about four inches and then mow it down to two, for example, you may open the door to disease or further weed growth—even if two inches is the proper height for the grass.

What to do: Mow at least once a week. Even a 10-day gap between mowings is too long. If a gap of more than a week does occur, adjust your mower’s blade height to avoid clipping off more than one-third of the grass height in the next mowing, then mow again a few days later to bring the lawn down to the preferred height.

Tip: Mowing twice a week will yield an even lusher lawn—frequent mowing is the single biggest reason why golf courses and professional baseball diamonds tend to look lusher than yards.

2. Overfertilizing. Excess fertilizer could seriously dehydrate grass, something known as “burning” the lawn. And even if a lawn escapes this fate, the excess fertilizer could make the grass grow faster than normal, ­potentially leading to scalping of the la­wn when it is mowed, as discussed earlier.

What to do: The amount of fertilizer recommended on the packaging is the maximum amount that’s safe to use. Spend a little extra for a “time-release,” or “slow-release,” fertilizer that supplies nutrients to the lawn slowly over a period of weeks, not all at once.

Choose a fertilizer that has about 50% of its total nitrogen as slow-­release nitrogen. To determine this, find the overall percentage of “slowly ­available nitrogen” (indicated in small print on the package) and make sure that it is about half the overall percentage of “total nitrogen” (which is the first of a set of three numbers joined by hyphens on the package).

3. Not knowing what type of grass you have. Grass is not just grass. Many different turfgrasses are grown in US lawns—Kentucky bluegrass, fescue and ryegrass are common in cold climates…Bermuda and St. Augustine grass are found in warmer parts of the country, to name just a few. But the vast majority of home owners do not know what type of grass is growing in their lawns. So they often buy the wrong seed (or seed mixture) to spread over areas of the lawn that have thinned. This results in patches of grass that look and feel noticeably different from the rest of the lawn or that grow at a noticeably different pace.

Not knowing what type of grass you have also means that you can’t care for your grass the way that it prefers to be treated. For example, different types of grass thrive at different heights.

What to do: Bring a sample of your grass to your local garden center, home center or hardware store—wherever grass seed is sold-and ask what type of grass you have. You can enter the name of this grass into a search engine to find Web sites from university extensions and other sources that provide mowing—height recommendations and other care tips for your specific lawn. (Add the word “mow” to this search if the initial search fails to turn up mowing ­recommendations.)

Examples: Kentucky bluegrass does best when its height is kept between two inches and three inches, while zoysiagrass tends to flourish at one to two inches.

4. Buying off-brand grass seed.

Bargain-brand grass seed is inexpensive for a reason—most often it failed to pass an inspection because there was weed seed mixed in with the grass seed. So if you plant bargain seed, there’s a good chance that you are introducing weeds to your lawn.

What to do: Pay a bit more for the seed that is at least 99.5% weed-seed free. By law, this statistic should be listed on grass-seed packaging.

5. Overwatering. Overwatering a lawn isn’t just wasteful, it also puts your lawn at risk. In fact, more lawns are damaged by overwatering than by underwatering. Overwatering increases the odds of getting lawn diseases…it can wash away fertilizer…and it can cause a lawn to grow faster than normal, increasing the odds that it will be scalped during a subsequent mowing.

What to do: Purchase a soil moisture meter so that you don’t have to guess when your lawn needs water. Simple meters are available in garden and home stores and online for as little as $10. If you are willing to spend much more and you have an irrigation system, opt for the UgMO PH100 ($450 per irrigation zone installed,, which uses underground soil sensors to automatically alert the irrigation system when watering is needed.

6. Bagging grass. Grass clippings provide much needed nutrients to your lawn. Contrary to widely held belief, leaving clippings on a lawn does not increase the odds of thatch problems—thatch is a layer of decomposing grass roots, not grass clippings.

What to do: If your current mower has a mulching mode, that’s the way to use it. If not, make your next mower a mulching mower. These are specifically designed to finely chop clippings and return them to the lawn. Mulching is easier, faster and better for your lawn than bagging.

7. Ignoring a new home’s special lawn needs. When a home is built, the surrounding land often is reshaped to encourage water to run away from the structure. One unintended consequence when the lawn is first planted is that it might be planted in soil that until very recently was subsoil, not topsoil. Subsoil has not had plants growing in it—then dying and decaying in it—so it lacks the nutrients that grass needs to thrive.

What to do: Be a bit more aggressive with the fertilizing schedule when you move into a newly built home—apply fertilizer in both May and June rather than waiting until July for the second application. However, do not increase the amount of fertilizer used per treatment.

8. Mowing with dull blades. Dull mower blades rip grass blades apart rather than making a clean cut. This rough treatment can make grass more susceptible to drought and disease. It also can make the grass appear white.

What to do: Sharpen your mower blades at least once a year—potentially several times a year if your lawn has lots of rocks or roots that often nick your blade.