Will shredded Fall leaves harm my lawn?

Many landscapers (such as out trainers) have been doing LELE for a number of years - they would not be doing this process if the results damaged the turf quality the following year! (Read their testimonials.)

Scientific research concerning leaf mulching on turf has been compiled by LELE team and by folks at the Westchester Cornell Cooperative Extension offices.

A number of studies exist and are referenced in the discussion of LELE effects on lawn and soil from Purdue University, University of Michigan, and Cornell University.

Here are two summary articles from Grounds Management magazine (online):

Additionally, Purdue researches have provided a useful summary on the topic of leaf mulch and turf - “Leaf Mulching Effects on Turf Performance” by Zac Reicher and Glenn Hardebeck. 

This short summary of their research states that the practice "increased soil microbial activity [which] indicates improved soil quality. Therefore, we expect that the heavy clay soils on which many new subdivisions are now built should improve as the trees mature and their leaves are mulched into the turf. Our data [also] suggested an increase in water-infiltration rates. This data was not conclusive but, combined with the increased soil microbial activity, suggests mulching tree leaves improves soil properties."

The Science Behind Lawn Leaf Mulching Initiatives

While there is limited scientific research into leaf mulching on lawns, we know of two studies that affirm the environmental claims we make: that mulching leaves into lawns reduces phosphorous pollution in waterways, and the practice (which reduces the need for leaf blower use and consequent noise and diesel fume pollution) has no adverse affect on turfgrass growth.

Mulching Leaves into Lawns Does Not Add to Thatch or Smother Turfgrass Growth

In a study published in the Journal of Turfgrass Management Vol. 3 (1) 1999, researchers at Cornell University tested the affect of mulching leaf litter into Kentucky Bluegrass over a three-year period. Red oak and Norway maple leaves were used in the study, which involved mulching a 12 cm layer of leaves into established turfgrass. The study concluded that yearly tree leaf deposition had no effect on Kentucky bluegrass shoot growth, visual quality, soil pH and thatch accumulation and thus “would be a suitable landscape/solid waste disposal method.” (Tree Leaf Deposition Effects on Kentucky Bluegrass [Poa patenses L.] by P. Nektarios, A.M.Petrovic, D. Sender)

Phosphorus Leaching

New York State has recognized the problems associated with phosphorus leachate from leaf litter left out for municipal collection and has advised municipalities to remove leaves from roads within one month.

However, research at the University of Adelaide, Australia showed that most phosphorus leachate from leaf litter (testing five tree species) is produced within 48 hours and observed the direction connection between impervious surfaces (asphalt) and receiving waters and the increased velocity of surface runoff increasing the potential for material to be transported directly into streams. (A comparison of phosphorus and DOC leachates from different types of leaf litter in an urban environment. Wallace, Ganf, Brookes. Freshwater Biology (2008) 53.

More Research on Turf and Soil

Paul Wagner, president of Soil FoodWeb New York, a soil testing laboratory and source of information concerning organic turf care, presented a talk about leaf mulch, soil organisms, and plant health at a Conservation Cafe event in 2011.  The talk is in two parts on YouTube, each linked below:

Soil Food Web (part 1)

Soil Food Web (part 2)

"Each plant group has levels of soil microbes that are considered ideal. For most cool season grasses balanced levels of soil bacteria and fungi are desired. Since bacteria and fungi retain plant nutrients, in order to make them available to the plant, high levels of predatory microbes like protozoa and nematodes must also be present. Protozoa and nematodes feed on bacteria and fungi and cycle nutrients."

"To maintain quality turf a good balance of nutrients is required, as well as a good balance of beneficial soil organisms."

"Quality compost has been well proven to add beneficial organisms to soils and also provides an excellent habitat and energy source for microbes already present. Compost helps soil retain nutrients, improves water holding capacity and porosity, as well as reduces soil compaction.

In an article in TurfGrass Trends, Dr. Eric Nelson of Cornell stated that 'Of all the natural organic materials commonly applied to turfgrass, composted amendments have been among the most consistently effective in reducing the severity of turfgrass diseases. Results of studies conducted over the past 10-15 years have clearly shown the potential for compost amendments to reduce the severity and incidence of a wide variety of turfgrass diseases, particularly when applied either as a topdressing, a winter cover, a root zone amendment, or as an aqueous extract' (Nelson, 1996)."

As quoted from "BIOLOGICAL TOOLS FOR GOLF TURF MANAGEMENT - A guide to the use of biological methods", Researched and written by: Jon Nilsson East Coast Compost, LLC and Paul Wagner Soil Foodweb New York, Inc.

More in-depth reading about the Soil Food Web - Soil Biology Primer [online]. USDA Natural Resource Conservation Service, Available: soils.usda.gov/sqi/concepts/soil_biology/biology.html, 2012

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