Should I Rake Grass Clippings or Leave Them on My Lawn?

Grass clippings on a rake
David Beaulieu

A reader with a large lawn and concerned about the extra landscape maintenance required to rake up grass clippings asked, "Can I leave them on my lawn? Or will they cause harm?" It is a question that many homeowners have, so the answer is worth sharing with everyone tasked with mowing lawns.

Should You Rake Grass Clippings or Leave Them?

Leaving them on a lawn that has healthy grass becomes a problem only if they are too thick (that is, the grass was too high when you mowed it) or the lawn is wet:

  1. When they are too thick, they mat down. 
  2. When the lawn is wet, grass clippings stick together (just as it is easier to make snowballs out of wet snow than fluffy snow).
  3. In each case, they block the healthy flow of air to your lawn.

If you mow the lawn before it gets overly tall, the mass of the grass clippings will not be sufficient to warrant raking (or bagging, if you use a bag attachment on your lawn mower). They do not contribute to lawn thatch build-up.

But what if you do not want to have to worry about getting the timing just right or bother with emptying out a mower bag? A good way to get around having to bag or rake grass clippings is to mow with a mulching mower. Mulching grass clippings chops them up finely enough that they cause no harm to the lawn. But regardless of the type of mower that you own, you should not be mowing when the grass is wet (if for no other reason than because it is dangerous to mow wet grass).

The advice above specified that leaving clippings on the lawn is all right, under the right conditions, provided that the grass in question is healthy. But if you have patches of diseased grass on your lawn, you should bag the clippings and dispose of them. Otherwise, you risk letting the disease spread to other areas of the lawn.

Air Flow and Lawn Diseases

Above, it was stated that when grass clippings are too thick or stick together due to wetness, they can block airflow to your lawn. This is unhealthy. Why? The reason is that poor air flow encourages disease. Any type of fungal disease, in particular, is more likely to occur under conditions where air does not circulate as well as it should. Here are some diseases that can attack a lawn due to improper handling of grass clippings:

  1. Brown patch.
  2. Dollar spot.
  3. Powdery mildew.
  4. Pythium blight.
  5. Rhizoctonia.

Why Grass Clippings Are Good for Your Lawn

Making a case for using a mulching mower and leaving grass clippings on lawns (under the right conditions, as outlined above) goes beyond stating that no harm will be done. Leaving this residue where it falls can be good for your lawn, your health (if you believe in green living), and your pocketbook.

The nutrients provided by the grass clippings allow you to lower your dependence on chemical lawn fertilizers, thereby saving money. They are especially rich in nitrogen. And this natural form of nitrogen acts as a slow-release fertilizer. You will never have to worry about its burning your lawn. Nor will it cause harm to pets or children.

An Alternative: Grass Clippings in Compost

If for whatever reason, you decide that you do not want to leave your grass clippings on the lawn (for example, you wish to avoid tracking them indoors), there is still no need to bring them out to the curb to have the city haul them away. That is a waste of organic matter. Instead, use them in your compost bin.

Grass clippings serve as a "green" component in compost and work in tandem with "brown" components such as the leaves you rake in fall. Freshly-cut grass blades are mainly water, which is why a huge pile of them deposited into a compost bin breaks down so fast. In the process of breaking down, they heat up your compost pile, which, in turn, helps the pile's other components to decompose more quickly.