Leave Them Alone

Fall management of leaves in the home landscape has been an evolving issue.  Thick layers of leaves left alone on our lawns can damage the turf, by blocking out needed sunlight.  The leaves also trap and hold moisture in the turf canopy, increasing the potential for lawn diseases.  It was also believed (incorrectly as it turns out – more on that later) that unraked leaves added to thatch problems in turf.  So we spend time and energy raking, blowing and removing them, which creates the follow up problem of how to dispose of them.  State and Federal regulations also provide limits on how to manage them.  We used to burn them, but have since learned that adds to air pollution, added carbon dioxide in the atmosphere and always posed a potentially risky fire hazard.  Composting is a great alternative, and many municipalities gather leaves raked to the curb to make leaf mold and compost for use in our home and public gardens.  One drawback to that method, however, is that leaves raked to the curb can easily be washed into the storm water system while waiting for pickup, which ultimately adds unwanted extra nutrients like nitrogen and phosphorus into our streams that foster algae blooms and eventually lead to dead zones in the Chesapeake Bay when the algae dies and the decomposition process uses up the dissolved oxygen in the water that is necessary for a healthy estuary ecosystem for crabs and oysters.  If we bag the leaves, they wind up taking up space in our landfills, so that’s not a good alternative either.  So what’s a responsible, environmentally aware homeowner to do?  Here are a couple of suggestions.

On-Site Composting

•    Compost them on site.  A 6-8 foot diameter ring made of chicken wire, or fencing material will easily hold a typical yard’s yearly accumulation of leaves.  After a year’s time, this will compost down and become a marvelous soil amendment on either your vegetable gardens, or landscaped beds.  If you’re concerned about the looks on your landscaped beds, then a thin layer of woody mulch of your choice on top of the leaf mold, and no one’s the wiser.  This organic material will improve the structure of your soil, feed beneficial microorganisms and worms, reduce compaction problems, and add those nitrogen and phosphorus nutrients which are considered pollutants when sent downstream, to your trees, shrubs, and flowers, reducing your need to augment with purchased fertilizers.  Chopping up the leaves will speed up the composting process, but is not necessary. Compost happens, pretty much on its own, as a natural occurrence of breaking down organic materials.  An energetic and industrious composter can do several things to speed up the process to as little as 3 weeks under perfect conditions, but the end product is pretty much the same as the lazy, but patient composter who does nothing but pile the leaves up and waits for a year or two before using the finished result.

On-Site Mulching

•    Instead of composting them, just use as a mulch on your landscaped beds, directly.  This works especially well in shady, dry areas of your landscape.  So long as the leaf layer is less than 4 or 5 inches, plants will have no problem poking up through the leaves in the spring.  The benefit to mulching your beds in the fall is sometimes described incorrectly as keeping the roots of your plants, trees and shrubs from freezing; to keep them warm.  That’s not accurate.  It’s to keep the temperature around the surface roots more even, gradually cooling and warming with the seasons thus smoothing out the natural temperature fluctuations and freeze/thaw cycles which can damage the plant. This method most closely matches what occurs in a natural forest ecosystem. If you want to speed up the warming of your soil in the spring, then you can gently rake them off at that time.  The only potential warning is if your landscape has a lot of Black Walnut trees, whose leaves contain a natural chemical called juglone, which can be detrimental to some plants.  It’s best to compost Black Walnut leaves for 6 months to mitigate any harmful effects of juglone.   See Ohio State Fact Sheet on Black Walnut Toxicity:
http://ohioline.osu.edu/hyg-fact/1000/1148.html

Mow Them

•    Don’t rake, or blow them, mow them.  A final run through of your lawn with a mulching mower, set at 3-4 inches, will chop up the leaves sufficiently to allow them to decompose in place and add their nutrients to your turf, again reducing the amount of fertilizer you need to purchase and add to your lawn.  Purdue University and Michigan State University conducted several studies to measure what the impact on turf would be using this method.  All those studies concluded that turf in home lawns benefits from this practice.  Purdue’s conclusions: 
•    Leaves have no effect on turf visual quality or color
•    Leaves have no effect on turf growth measure by clipping weights
•    Leaves have no effect on mat or thatch depth
•    Leaves have no effect on soil pH or nutrient availability
•    Leaves have no effect on incidence of red thread, pink patch or dollar spot
•    Leaves have no effect on weed infestation
“The results are very positive and suggest that mulching tree leaves is an economical method of disposal with little risk of decreased turf performance. Our results are similar to those from Michigan State University and Cornell University and we are now very confident in recommending professionals and homeowners to mulch tree leaves into the turf each fall.”

On the Web:
http://www.agry.purdue.edu/turf/report/1999/page24.htm
http://grounds-mag.com/mag/grounds_maintenance_leaves_turn_litter/
http://pubs.ext.vt.edu/430/430-521/430-521_pdf.pdf