An Easy Answer
It's a question we all face when mowing: Should I bag my clippings or leave them on the lawn? In most cases, the answer is easy: Leave the clippings on the lawn! Leaving the clippings will save you time and energy, and it will return valuable nutrients to the lawn.
Like Free Fertilizer
The most important thing you can do for your lawn is to feed it regularly, and grass clippings contain the same beneficial nitrogen, phosphorus, and potassium nutrients as fertilizer. In fact, clippings can provide as much as one-third of the annual feeding requirement for your lawn.
Less Work for You
In addition to recycling nutrients back into the soil, leaving the clippings will cut down your mowing time and relieve you of the chores of emptying the grasscatcher and hauling bags of clippings out to the curb. It may also be keeping your clippings out of the landfill, depending on how your town handles yard waste.
Some Simple Guidelines
There are a few things you can do to help keep your grass strong and looking good when you leave the clippings. Keep your mower blade sharp and mow regularly at the recommended cutting height for your type of grass. Avoid mowing when the grass is wet. If the grass gets so long that mowing at your normal cutting height will remove more than one-third the length of the grass blades, raise the height on your mower. Mow once at the raised cutting height, then again in a different direction at the normal height. Avoid surge growth by using a slow-release fertilizer such as Scotts® Turf Builder®.
Not a Thatch Problem
Contrary to a popular lawn myth, leaving clippings on the lawn does not cause thatch, which is a layer of partially decomposed grass-plant parts between the soil and live grass. Grass clippings are mostly water, so as long as you mow regularly at the right height, they will break down and disappear rapidly.
The Exception: when Bagging is Okay
There are some circumstances when collecting your grass clippings is warranted. If you see signs of lawn disease, pick up the clippings to avoid spreading the fungus. Grass clippings can also be collected for use in a compost pile or as mulch, unless you recently applied a weed control product to the lawn. Some folks bag their grass clippings for aesthetic reasons or to keep the clippings from being tracked into the house. In most cases, following mowing guidelines will avoid clumps that detract from a lawn's appearance and will keep the clippings small enough to filter down into the lawn.