Don't P on Your Lawn

June 2008

The buzzing of lawnmowers fills the air on any lazy summer afternoon in the suburbs. The perpetual battle to maintain lawns fills many an hour and consumes many a dollar. Fertilizer, one common tool in the battle, presents challenges that should make any homeowner think twice about how they use it. In the wrong dosages or at the wrong times, fertilizer can be more of a cost than a benefit. Therefore, the Lake Champlain Committee has been closely involved with the Don’t P on Your Lawn Campaign, which encourages homeowners to switch to phosphorus-free fertilizers. 

Lawns and gardens do need the nutrients that fertilizers provide, but frequently those nutrients are already available in the soils without need of enhancement. Typical fertilizers contain three types of nutrients, nitrogen, phosphorus, and potassium. Each bag of fertilizer has three numbers on it representing the composition of these nutrients.

Fertilizers without phosphorus (the middle number on the bags) are usually sufficient for lawns in the Champlain Valley. While nitrogen not taken up by plants can escape in groundwater or to the atmosphere, phosphorus attaches to soil particles and accumulates over time. Thus, regularly fertilized soils often do not need any more phosphorus. Furthermore, many suburban homes in the Champlain Valley are built on former farm fields that had received fertilizer inputs for decades, and soil phosphorus concentrations can be quite high. 

Unfortunately, excess phosphorus has detrimental affects on water quality. Fertilizer from phosphorus can reach water when some of it is spilled on sidewalks and driveways or when fertilized soil erodes. Once in the water it acts as a fertilizer, just as it did on land, but people tend to dislike weeds and algae in the water. Who wants to swim in a green lawn?

The problem of excess phosphorus in waterways has accelerated greatly. “Until the 1950s, fertilizer manufacturing facilities were relatively small and produced fertilizers tailored to the soil needs of area farmers, commonly within a 100-mile radius”, according to the Florida Institute for Phosphate Research. Then, “In the 1960s, more concentrated phosphates began replacing normal superphosphates as the primary fertilizer commodity, turning what had been strictly a mining business into chemical production.” That meant phosphorus was being moved from distant places to accumulate in far-flung watersheds like the Lake Champlain Basin. 

Many communities throughout the United States have gone so far as to ban phosphorus from lawn fertilizers. The first such ban, in metropolitan Minneapolis, was enacted in 2001. By 2004 it had been expanded throughout the state of Minnesota. Various municipalities have followed suit in Wisconsin, Michigan, Illinois, and Florida.

Ecology isn’t the only reason to restrict fertilizer use, economy comes into play too. “The cost of products such as mono ammonium phosphate has more than doubled since last year”, and “(p)hosphate fertilizer shortages are expected to last for several years, keeping the price of commercial fertilizers high”, according to producer.com a purveyor of agricultural news. The principal driver of increased costs seems to be an increase in demand. According to The Fertilizer Institute, worldwide demand for phosphorus has increased by 12%. (Increases in nitrogen costs reflect increasing fuel costs as well as demand changes).

When fertilizer is used, it should be applied only in the fall to established lawns. Spring and summer applications stimulate leaf growth at the expense of roots. These applications can help weeds because they invest in broader leaves. Cornell Cooperative Extension recommends, “a single application…between Halloween and Thanksgiving (about 2 weeks after your last mowing)”. One simple alternative (or at least complement) to fertilizer is to mulch grass clippings back into the lawn. This increases the soil’s organic matter and retains the nutrients from clippings on site.

So in short, most lawns don’t need fertilizer, it’s expensive and getting more so, and when it gets into the water it pollutes. If anyone needs a reason to avoid adding phosphorus to their lawn it seems those are three good ones. For tips on environmentally-friendly lawn care, sources in the region for phosphorus-free fertilizer and other information about the Don’t P on Your Lawn campaign visit http://www.lawntolake.org/.