Does Your Lawn "P" in the Lake?

Our lawns are symbols of the American Dream--synonymous with success, paired with white picket fences to signal affluence and security. When our grass looks parched, it’s tempting to water and fertilize to achieve that bright green landscape. But the products we use to encourage prolific lawn growth may end up fueling less-welcome species, including cyanobacteria, when they end up in Lake Champlain. This is especially true for phosphorus, identified by “P,” its chemical symbol. Luckily, Vermont and New York have laws in place that make it easy to avoid applying “P” to your yard, only to have it end up in the lake – if you know what to look for when you’re shopping for yard and garden products. 

Bagged lawn fertilizers are labeled with three numbers indicating the ratio of three nutrients: N-P-K, or nitrogen-phosphorus-potassium. Lawns and gardens, like all life on earth, require these nutrients; however, they are available in varying degrees in naturally occurring soils.  

Phosphorus, the middle number on bagged fertilizer, is particularly abundant in the Champlain Valley. While nitrogen not taken up by plants can escape into groundwater or the atmosphere, phosphorus attaches to soil particles and accumulates over time. Many suburban homes in our region are built on former farm fields that received fertilizer inputs for decades, and soil phosphorus concentrations can be quite high.  

While essential for life, phosphorus is a major water pollutant and one of the primary water quality concerns for Lake Champlain. The same nutrient that grows grass feeds cyanobacteria blooms and contributes to eutrophication, where excessive weed and algal growth blocks sunlight, depletes oxygen, and ultimately leads to degraded water quality and ecosystem health. 

Given the damage added phosphorus can do to aquatic life, in 2012 both Vermont and New York passed laws banning phosphorus from regular lawn fertilizers. However, phosphorus-containing fertilizers are still sold in lawn and garden stores, as you can use them when starting a new lawn or if a soil test proves you have insufficient phosphorus. It’s important to know what to look for to avoid inadvertently feeding species you’d prefer not to encourage.   

The Lake Champlain Committee is one of the founding members of Lawn to Lake, a collaborative program promoting healthy lawn and landscape practices in the Lake Champlain Basin, including the Don’t “P” on Your Lawn Program. Here are a few for tips for a lake-friendly lawn – check out lawntolake.org for more: 

 1. Use only phosphorus-free fertilizers—look for the zero 

The three numbers on a fertilizer bag indicate the nutrient percentages of nitrogen, phosphorus, and potassium (N-P-K) in that order. A zero in the middle means it’s phosphorus-free; for example, 22-0-15. Fertilizers sold in lawn and garden stores should be clearly marked as either “lawn fertilizers” which should not contain phosphorus, or as “lawn starters” which usually do contain phosphorus. 

 2. Take a soil test—learn about your lawn 

A soil test can tell you about the nutrient levels, organic content, and pH (the soil’s acidity or alkalinity) of your lawn or garden area and what you need for healthy plant growth. The University of Vermont Agricultural and Environmental Testing Lab offers basic soil testing.  In New York State, your county’s local office of Cornell Cooperative Extension (CCE) can help. 

 3. Fertilize once a year—apply in the fall, not the spring 

The application of fertilizer in the fall helps grass survive the winter and prepares it for successful growth the following spring.  

 4. Water less—grass is hardy 

Even without watering, grass will survive droughts, like the one we are experiencing now, by going dormant. Water in the early morning, when the air temperature is cooler, and only when it rains less than one inch during the week. 

5. Mow higher—raise the blade 

Maintain a grass height of three to four inches and cut off no more than 1/3 of the blade height during each mowing—this allows grass roots to deepen which is good for soil health and helps prevent runoff. Leave grass clippings on your lawn to build nutrient and organic matter. 

6. A friendly flower reminder—“weeds” can be beneficial 

Flowers like common dandelion, violets, and white clover offer numerous benefits: dandelions and violets provide food to pollinators and clover roots contain nitrogen-fixing bacteria—a natural way to fertilize your lawn if it’s lacking nitrogen. These “weeds’ also have deeper roots than regular turf grass, which is beneficial for soil health and water retention. 

Grassed lawns are the largest irrigated crop in the U.S., more than corn, soy, and vineyards combined, yet we derive no food from their fruits. In the endeavor to grow lawns, we not only reduce native biodiversity of our landscape, but we alter the chemical makeup of our soils and water. The American Dream that our lawns have come to represent is one that operates under the assumption that clean water is a given. If our suburban landscape is at odds with the health of our lake, perhaps the dream should shift toward one where we steward our lands to protect our waters.