Yard Waste
Americans love their lawns. We fertilize and water grass to keep it green for as long as possible, we harvest the “crop” by mowing and we even rake the fallen leaves off so we can see it during autumn. Unfortunately, the way we dispose of our “harvest” has the potential to harm our lake.
Some people might dump their yard waste right into the lake. They will say they are “creating fish habitat” or “feeding” the fish. What they are really doing, however, is polluting their lake. The best thing for your lawn (and the lake) is to leave the grass clippings on the ground. If you have a mulching mower with a good, sharp blade, you are doing your lawn the most good. Thatching is not an issue if you mow often enough. If you simply must pick up the clippings, or if you notice clumps of grass from the previous mowing, you can collect your grass clippings and use them as mulch around landscape plants to block out sunlight and hold back weeds, as well as release nutrients. Composting is another great solution.
| Source | % Nitrogen | % Phosphorus |
|---|---|---|
| Cow Manure | 0.7 | 0.5 |
| Sheep and Goat Dung | 2.0 | 0.5 |
| Poultry Manure | 2.9 | 1.3 |
| Lawn Clippings and Leaves | 3.0 | 0.3 |
Table data source: FAO.org
The bulk of the sampling work done by the Lakes of Missouri Volunteer Program (LMVP) is to monitor nutrients and algae. Excess nutrients contribute to excess algal growth and make our lakes look green. When lawn clippings and leaves are completely dried, a full 3% of the remaining weight is nitrogen, 0.3% is phosphorus. While yard waste has 40% less phosphorus than found in cow manure (per pound), it has more than 4 times the nitrogen of cow manure.
Algae in our lakes can typically be controlled by limiting the nutrients nitrogen and phosphorus. Phosphorus is usually the nutrient in the shortest supply, so controlling phosphorus is often the best long-term way to manage algal growth. Given that the LMVP measures nutrients in parts per billion (µg/L), a little phosphorus goes a long way. As reported in The Water Line in 2008, a typical Ozark forest drops 6 to 7 pounds of phosphorus per acre each year as leaf litter. If your lakefront lot is a quarter acre, and your tree density is one-fourth that of a typical Ozarks forest, your trees are dropping roughly 181,440,000 micrograms (µg), or 6.4 ounces of phosphorus each year. Now imagine if you and several of the neighbors in your cove are all dumping your leaves in the lake. Repeat every year. Notice that this calculation doesn’t include grass clippings; increase the numbers if those are going into the lake.
On average, 100 pounds of dried yard waste (including grass clippings) contains 4.8 ounces of phosphorus, which equals 136,000,000 micrograms (µg). Adding that amount of phosphorus to 1.4 million gallons of water will result in a final phosphorus concentration of 25 µg/L, the same as Lake of the Ozarks near the dam. Though not quite the same scale as “The Lake”, 1.4 million gallons is equal to 4.3 acre feet, a volume of water one acre in size and 4.3 feet deep.
Leaves and lawn clippings aren’t just a problem when they’re dumped directly into the lake. People may dump their grass clippings in “that gulley behind the house” or rake their leaves into the creek. Though it’s not as direct, if you live in a lake’s watershed, much of the nutrients will eventually get to the lake.
The leaves of overhanging trees will naturally fall into the water and contribute nutrients. This is a driving factor in some streams, providing valuable nutrients to the benthic (bottom-dwelling) invertebrates that are integral to stream food webs. Leaves that hit the land in forested areas, however, tend to stay near where they fell, usually travelling less than 2 feet. Most of the nutrients from these leaves would be available for the tree that dropped them or vegetation surrounding that tree and wouldn’t reach the stream or lake. Grass clippings are not a naturally occurring component of an ecosystem, yet turf grasses are the single largest irrigated crop in the United States, with three times more irrigated land devoted to growing grass than to growing corn. It’s unfortunate that our grass clippings don’t have as much value as our food. People would be much less likely to dump a bushel of corn into their lake than they would a bag of grass clippings.
Some tricks to composting yard waste
Compost grass clippings in thin layers to avoid matting, ideally interspersed with layers of autumn leaves.
Let the grass clippings dry out for a couple of days before composting to speed the decomposition process.
If you have too many grass clippings in your compost pile, turning it every few days will speed up the process.
When you’re done, you‘ll have a pile of great, nutrient-rich soil, something that’s in short supply in southwest Missouri.