Is it OK to mow fallen leaves? The answers to all your fall lawn questions.

Is it OK to just mow leaves on the lawn throughout the fall season? I am trying to save some time this fall.

— Janel Fitzpatrick, Buffalo Grove

Leaves have begun falling and will quickly increase in the next couple of weeks. I have had good results using a mulching mower to mow my lawn — including all the fallen leaves — throughout the fall season. It is important to use a mulching mower for this strategy so that the leaves get ground up into small pieces. My yard is mostly shaded by large oak trees, so lots of leaves end up falling on the grass. Sometimes in late fall, I do need to use a rake and leaf blower to remove excess leaves left after mowing that could end up smothering the lawn. Try to mow weekly during the fall to keep up with the leaves as they fall. It’s a judgment call as to what constitutes too deep of a layer of shredded leaves left on the lawn. You should see more grass than leaves once you have mowed the lawn. Using a bag to collect the grass clippings and leaves will result in a clean and manicured appearance for your lawn. The ground-up leaves and grass clippings will be good for a compost pile.

As the fall season progresses, I drop the mowing height to 3 inches and then to 2 1/2 inches with a final cut at 2 inches. Gradually reduce the mower height until you’re cutting grass at that shorter length. You should not remove more than one-third of the total blade length with each cut. Mowing at a lower height will grind up the leaves more effectively and save lots of time raking. Mulching mowers do not work as well when the leaves are very thick, or when the grass is very long or wet, so it takes longer to finish mowing. Reduce the width of the grass you are cutting with each mower pass to reduce the strain on the engine and get a better cut. You may need to make some extra passes with the mower in late fall to better grind up the leaves.

The general rule is to keep mowing the lawn as long as it is growing, which will depend on the weather. If your lawn was fertilized this fall, you will likely get more growth, making late-season mowing more important so that the lawn does not get too long and mat down over the winter. Bluegrass generally stops growing when daytime high temperatures are consistently below 50 degrees Fahrenheit. A hard frost in the 20s will usually slow but not necessarily stop the lawn’s growth for the year. An early snowfall that quickly melts will generally have little influence on stopping the lawn’s growth. Avoid mowing or even walking on your lawn when there is frost present to avoid damaging the crowns of the grass. The heavier the frost, the more potential damage you can do by walking on the lawn.

For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.