Leave it or bag it ... that is the question

By David Sprague

OSU Extension master gardener volunteer

Summer is here to stay for a while and so is the summer chore of mowing the yard. One question we get in the clinic about yard mowing is, “What should I do with the grass clippings? Should I leave them on the lawn or bag them?”

While the answer to this question is partly a matter of personal choice, from a horticulture standpoint there is a preferred answer. Let’s take a look at what this answer is and what some of its conditions are.

Research from universities shows that the best thing to do with lawn clippings is leave them on the yard. Clippings are a source of plant nutrients and organic material for your lawn. Grass clippings consistent of about 4 percent nitrogen (N), and contain phosphorus (P) and potassium (K), plus small amounts of other plant nutrients. If you remove your grass clippings, you are removing up to 50 percent of the nitrogen in the fertilizer you applied to your yard. Research at the University of Missouri shows that grass clippings can supply 25 percent of a lawn’s total fertilizer needs. Leaving grass clipping on the lawn saves nutrients and saves you time and money.

One reason people bag the clippings is they think they will cause thatch. They do not. Thatch is a layer of undecomposed organic matter that builds up between the soil’s surface and the actively growing green vegetation. Grass clipping are mostly water, 75-85 percent water by weight. Clippings will dry out and break down rapidly after mowing and coming in contact with the soil’s microbes. The main causes of thatch are over-fertilization and over-watering. The primary components of thatch are grass stems and roots that accumulate because these plant parts grow faster than they breakdown. A thatch layer thicker than 1/2 inch can cause lawn problems. Core aeration and a top dressing of good top soil or compost will help the thatch to break up and decompose.

There are a few things to consider when mowing the lawn and leaving the clippings. OSU Extension says to keep clippings off driveways, sidewalks and storm drains. Leaving clippings there can wash into the watersheds where their nutrient content contributes to algal blooms in ponds and lakes. For healthier lawns, leave the grass taller, cutting it at 3 to 31/2 inches. Don’t cut off more than one-third of the grass blade at a time. These actions will keep the grass roots strong.

This summer save yourself some work and help your lawn at the same time – leave the grass clippings on the lawn.

For more information on grass clippings, go to: http://go.osu.edu/lawnclippings