Here is an updated version of a blog post that was originally published on November 15, 2013. Turf Extension Educator Sam Bauer has been interviewed about this topic in several great articles since then so be sure to check out the links at the end of the blog post!
Are you looking to avoid the leaf raking process this weekend? The real answer to the above question is NO, but it comes with one catch. The most important point with fall cleanup is that the tree leaves are not covering a significant portion of the turfgrass canopy. 10-20% coverage of your lawn might be okay, but I certainly would make sure the leaves aren’t covering any more than that. Excessive leaf matter on your lawn going into winter is bad for several reasons. First, it will smother the grass and, if not removed very soon in the spring, it will inhibit growth. Second, it can promote the snow mold diseases. And finally, turf damage from critters (voles, mice) can be more extensive in the spring.
The homeowner basically has three options to make sure that leaves are not covering a significant portion of their lawn:
1) Rake them up or use a blower; then compost the leaves or dispose of them
2) Use the bagging attachment for your mower; then compost the leaf/grass mix or dispose of
3) Mulch the leaves with a mower (i.e. chop them into small pieces so they will fall into the canopy). This is my preferred option because the nutrients and organic matter will benefit the lawn and soil. Some leaf types have been shown to reduce weed seed germination when mulched into a lawn canopy (maples, others). The leaves of some particular tree species (legumes like honey locust, others) might actually add a significant amount of nitrogen to lawns because these species fix nitrogen from the atmosphere just like soybeans, so higher leaf nitrogen contents in these leaves is possible. Additional resources for these two concepts are here:
Tree leaves and weeds (pdf)
Nitrogen content tree leaves (pdf)
Successfully mulching leaves into a lawn canopy requires more frequent mowing in the fall and possibly several passes with the mower to mulch the leaves sufficiently. Specialized mulching mowers can also be purchased, and these mower types will also be beneficial year-round to mulch grass leaves into the canopy. Chopping leaves into small pieces is important.
Tree leaves that have built up to this level in your lawn would not be practical to mulch into the lawn canopy. Removal would be required in this situation. Photo: Sam Bauer
Moderate levels of tree leaves can easily be mulched into a lawn canopy, such as the situation shown here. Photo: Sam Bauer
For more information from Sam Bauer regarding raking and leaf mulching, please read the following articles:
Stop raking your leaves! By Christopher Ingraham, The Washington Post
Spare the rake, spoil the lawn? Getting at the root of our fall ritual. By Mary Jane Smetanka, Star Tribune