November 10, 2011

University of Arkansas, Division of Agriculture
Turfgrass Science Program (http://turf.uark.edu) – Turf Tips

To leaves or not to leaves

I live in an older neighborhood in Fayetteville called East Oaks. It is well known for its beautiful, mature oak, hickory, and maple trees and those trees make for some comfortable living every summer when the thermometer starts approaching triple-digits. Unfortunately, during the months of October and November, my neighbors and I fondly refer to the same neighborhood as the $%/!@# Oaks (see photo at right). These are the months that our Saturdays are spent trying to corral all the fallen leaves and get them out to the street so they can find a home at the city compost facility. Every year, I get lots of questions from my neighbors about mulching leaves, raking them every week, or just waiting until they all fall to clean them up. Although there is not a one-size-fits-all recommendation, below are some things to think about if you have lots of leaves on the lawn.

What kind of grass are you growing?

In the northern half of Arkansas, most lawns that have lots of trees and leaves are planted to cool-season grasses like tall fescue or bluegrass, while you will find more St. Augustine or centipedegrass in central and southern Arkansas lawns with trees. The fescues and bluegrasses are cool-season grasses that have the most active growth in the spring and the fall when temperatures are cool and there is adequate moisture. St. Augustine and Centipedegrass are warm-season grasses that are actively growing from late spring until early fall and dormant in the winter.
Although the cool-season grasses have good shade tolerance and will not be significantly harmed by leaving leaf litter on the lawn for a period of time, it is important to remember that fall is the best time of the year for the grass to recover from the summer and when the lawn will respond best to fertilization .  So, it is always best to keep the leaf litter at a minimum during this period so the turf is getting maximum light and can really get thick before the winter period. This time of the year is also when many lawns are getting their best light since the tree shade is at a minimum once all the leaves drop. It is even more important to keep the leaves off the lawn if any re-seeding was done to the lawn earlier in the fall, as the seedling turf will not be as tolerant of extended shading as a mature lawn.
Although the warm-season grasses are generally not as shade-tolerant as the cool-season grasses, one advantage is that they are going into the winter dormancy period when the leaves are falling. Since the grass is not trying to grow and capture light, the turf is not missing out on a key growth period like the cool-season lawns will. As such, it is not as critical to regularly keep the leaves off the lawn and you can likely wait until they all fall to deal with them.

Mulching vs Raking

The issue of raking the leaves or mulching them back into the lawn (see photo at right) is one that we don’t have a lot of local data on, but most studies that have been conducted show that mulching leaves back into the lawn causes no negative effects on the turf and can even return some nutrients and organic matter to the soil that can have long-term positive effects on the lawn. A good friend of ours at Michigan State University, Dr. Thom Nikolai, conducted several studies back in the 90s on mulching various amounts and types of leaves into several types of cool-season turf. He found no negative effects of mulching leaves at a rate of up to 100 pounds of dry leaves per 1000 sq ft into both bluegrass lawns as well as low-maintenance lawns. A summary of that work can be found at the following here .
Several things should be kept in mind if you plan to mulch your leaves. First, there is likely a maximum amount of leaf litter that the lawn could take before some negative effects are noticed. Again, I am not sure there is a firm number here, but if you start seeing an accumulation of 1 inch of litter at the soil surface and it is not rapidly decomposing, it would be a good idea to rake the leaves for a period and not add more to the layer. Secondly, it is best to mulch the leaves as soon as they start falling, as they will decompose more rapidly while the soil temperatures are still warm while decomposition will slow later in the fall. Waiting until the end of the fall to mulch all the leaves will not only be hard on the mower, but will also lead to a thicker leaf layer since decomposition will be significantly slower as winter approaches. Finally, if you are mulching the leaves, it is best to maintain a relatively high mowing height (3”) so there is more canopy for the mulched leaves to hide in and they will not be as obvious when you look at the lawn.
If you want to rake the leaves, just remember to put them into compostable bags for pickup or dispose of them at a facility where they will be composted and can be returned to the soil. It is never good business to dump leaves into a landfill or into an area where they could lead to nutrient release into surface waters as they decompose. Many of the larger cities in Arkansas have curbside pickup of lawn and leaf debris and the material is composted and can be used by residents the following season.

Here’s hoping that if you have lots of leaves on the lawn, you also have a few kids around the neighborhood (or the house) that want to make some spending money by either raking them or mulching them into the lawn for you.

Wishing you all a Happy Thanksgiving and GO HOGS!!

Mike Richardson

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