Data-Driven Viewpoints: Water Quality vs. Lawn Care Practices

by Brian T Lynch, MSW

Most folks know that grass clippings are harmful when they get into lakes and streams.

I've noticed there are a few homeowners and even some lawn service companies taking shortcuts. I see places where homeowners and landscapers are disposing of yard waste in wetlands from which a brook emerges, a brook that the state DEP has classified as a “C1” protected water source. Most recently I saw a stream monitoring site in Succasunna in which copious amounts of grass clipping had just been dumped by a commercial landscaper.

Dumping anything into a lake or a stream is illegal in New Jersey and most states. It doesn’t matter if it is organic, inorganic, a living, or a non-living thing. So, dumping grass clippings into that creek beside your home, or into a lake, is illegal and reportable to the New Jersey DEP (1-877-warndep). Even when we blow or sweep grass clippings and leaves into the street, it ends up in our streams and rivers when the next big rain washes them down storm drains and into a nearby stream.

In general, lawn clippings contain around 4% nitrogen, 0.5 to 1% phosphorus, and 1 or 2 % potassium by weight. Nitrogen and phosphorus are a significant concern for water quality as they can cause explosive growth of algae and nuisance vegetation (eutrophication). In addition to this nutrient loading, grass clippings may contain toxins from herbicides and insecticides applied to a lawn. These chemicals may or may not break down during composting depending on the chemical composition of the toxins and the conditions under which they get composted. But, when grass clippings do get into a stream, any toxins they contain rushes downstream before it has a chance to decay. As a result, toxins may end up in reservoirs and the tap water we consume. Some chemical toxins can even infiltrate through the ground to aquifers below, contaminating wells.

Is this all just talk, or are lawn products and yard waste actually degrading water quality around here?

If you live on the west side of Mine Hill or in Succasunna, I can answer that. The Raritan Headwaters Association has stream monitoring sites in those locations. It publishes an annual water quality “Report Card” on the internet. The two main tributaries that flow into Sunset Pond (Mine Hill Beach) had a failing grade last year for their "ortho phosphorous" content. In other words, both streams have a nutrient overload, most likely from fertilizer runoff or yard waste entering the streams. They failed on several other factors as well, including their "specific conductance" (too much road salt). We can and must do better.

So, what can we do to improve the water quality? Is there a better way to deal with grass clippings?

I'm glad you asked!

When it comes to grass clippings, the less we do, the better. Don’t pick up your grass clippings at all (unless it is to prevent the mower from shooting them into a lake or stream). Instead, mulch-cut your lawn and let the clipping fall between the blades of grass. This method will,

Save you time spent on collecting and disposing of the clippings.
Help your lawn retain moisture and save on how much you have to water it.
Add hummus to your soil which can improve its structure.
Feed worms and beneficial microbes that help keep soil healthy (think probiotics), and
Grass clippings will decompose and return nutrients to the soil.

If you are worried about thatch build-up, properly mulched grass clippings don’t contribute to that problem. The only downside is you may have to switch to a mulching deck mower or purchase mulching blades for the one you own. If you try mulching with your current lawnmower but see grass clippings lying on the grass after a pass, your machine isn't mulching properly. If you use a commercial lawn service, they may not have dedicated mulching deck mowers for the job. A good mulching mower should cut the grass in small enough pieces that most of them drop down between the grass to the soil below.

The NJ DEP has a goog flyer on eco-friendly lawncare tips (see below).

Just a note on municipal compost. Don't use it if you don't know for sure that certain herbicides and pesticides are not present in the mulch. Residues of Picloram, Clopyralid or Aminopyralid Herbicide Create Killer Compost. From the article:

"Minute concentrations of picloram, clopyralid and aminopyralid, as low as 1 ppb (parts per billion), can be lethal to sensitive garden plants such as peas, beans, lettuce, spinach, tomatoes and potatoes. Most pesticides, including herbicides, break down quickly in the composting process. Picloram, Clopyralid and Aminopyralid do not. These chemicals are:
Easily absorbed by plants.
Remain chemically stable and intact in both live and dead plants.
Do not breakdown substantially in animal digestive tracts so contaminate manure, urine and bedding with residues.
Breakdown very slowly in composts and soils with an estimated half-life of 1 - 2 years.
Affect sensitive crops at very low concentrations - 1-3 ppb.

I hope you find this information helpful.