Your lawn's environmental impact can be positive or negative, depending on how you take care of it. In Harmony Sustainable Landscapes.

Your lawn’s environmental impact can be positive or negative, depending on how you take care of it.

Have you thought about the environmental impact of your lawn? Of all our lawns?

According to research by NASA scientist Cristina Milesi, there is more acreage in lawns in the United Stations than in croplands. “Even conservatively,” Milesi says, “I estimate there are three times more acres of lawn in the U.S. than irrigated corn.”

Milesi’s research found that lawns occupy over 128,000 square km (over 79,500 square miles). That is 13,000 square miles bigger than the state of Washington.

People love their lawns. Lawn mowers, fertilizers, irrigation equipment, insecticides and herbicides are big business. Americans spent $29.1 billion on lawn care in 2015, according to a survey conducted by the market research firm Mintel.

All that lawn care can translate into harmful environmental impacts. Fertilizer and pesticides may end up washing off into nearby streams and lakes. People use vast amounts of water on their lawns, reducing water available for stream flows and fish. Lawn mowers can pollute the air.

The role of grass clippings

There is good news: lawns have the potential to store carbon and reduce climate change. It depends on what we do with the clippings.

Milesi ran a number of model simulations to determine the environmental impact of lawns. She used different amounts of fertilizer, watering schedules, and either leaving the cut grass on the lawn or removing it.

She found that a well-watered and fertilized lawn is a carbon sink. If people leave their grass clippings to decompose on the lawn, the U.S. lawn area could store up to 16.7 teragrams of carbon each year. According to NASA, “that’s equivalent to about 37 billion pounds—the weight of about 147,000 blue whales.”

Milesi was a bit surprised to find that lawns could be a big carbon sink. When grass decomposes, it releases carbon dioxide into the atmosphere. But apparently grass is more efficient than she expected.

Decomposing grass also produces nitrogen, which helps it grow. The growth boost more than makes up for the carbon being released.

When grass clippings are picked up at the curb and sent to a commercial composting facility, lawns still have a positive impact on climate change, although at a much lower level. They store about 5.9 teragrams of carbon per year (about 13 billion pounds).

The worst impact is when clippings decompose in a landfill. The oxygen-poor environment increases production of methane, a potent greenhouse gas.

In addition, gasoline-powered mowers may harm air and water quality. The US Environmental Protection Agency estimates that gas-powered lawn and garden equipment emitted 26.7 million tons of pollutants in 2011. This is 24−45 percent of all nonroad gasoline emissions. And over 17 million gallons of gas are spilled each year refueling lawn and garden equipment.

Mowing: improving your lawn’s environmental impact  

  • Leave the clippings on the lawn when you mow.
  • Consider buying a mulching mower. These mowers blow the clippings down into the grass blades, so your lawn looks tidier.
  • Replace your gasoline-powered mower with a battery-powered or reel mower.

The role of water

The average American household uses 320 gallons of water a day. About 30 percent of that amount is used for watering lawns and gardens. Perhaps half of landscape water is wasted due to evaporation, wind, or runoff. Does that mean you shouldn’t water?

If you read our blog regularly, you have probably noticed that we keep saying that you need to water your lawn, trees and other plants in the summer. Your plants require water to keep them alive and healthy. Green spaces have important ecological and emotional value.

But what about the environmental impact of all that water? The research cited above indicates that a healthy lawn has more value as a carbon sink because it is actively growing.

If you stop watering completely, your lawn will become weak and thin, allowing for the encroachment of weeds, moss and insect pests. What will be the environmental impact of treating those problems?

Water: improving your lawn’s environmental impact

  • Water your lawn to keep it healthy, but don’t overwater it. Your lawn needs about an inch a week to stay alive and healthy in summer.
  • It is better to water slowly and deeply once or twice a week than to water a little every day. That will encourage your lawn to grow deep roots, reducing the potential for drought stress.
  • Water your lawn early in the day, before it gets hot, or in the evening. Note that evening watering can lead to problems with diseases.
  • If you’d like to reduce lawn watering in the summer, your lawn still needs an inch of water at least once a month to keep it alive.
  • If you have an automatic irrigation system, take time to calibrate it to minimize water applied to your yard. And invest in a rain sensor so you are not watering unnecessarily.
  • If you use sprinklers, test them out to make sure you are not overwatering. Here is a video on how to measure an inch of water.

The role of pesticides and fertilizers

The US Environmental Protection Agency has estimated that 59 million pounds of active pesticide ingredients are used on homes and gardens each year. This includes 28 million pounds of herbicides, 14 million pounds of insecticides and 17 million pounds of other types of pesticides.

Pesticides may run off the lawn when it rains, harming local water quality. Pesticides have been found in local streams at levels high enough to harm salmon and other aquatic life. Many of the pesticides found are those commonly used by homeowners on lawns and gardens. Pesticides are also harmful to birds, bees and other wildlife.

Fertilizers also have the potential to run off the lawn when it rains. According to the US Environmental Protection Agency, “Nutrient pollution is one of America’s most widespread, costly and challenging environmental problems.”

Nitrogen from fertilizers may cause algae blooms in lakes. When the algae die, they starve the lake of oxygen. Nitrogen can also harm groundwater and air quality.

Pesticides and fertilizers: improving your lawn’s environmental impact

  • Don’t expect to have a perfect, weed-free lawn. Most lawns look fine with some weeds. Focus on growing a thick, healthy lawn that will outcompete weeds. Here is a link to our blog post about how to grow a healthy lawn.
  • Avoid the use of any insecticides as they kill insect diversity and beneficial insects. The best approach to deal with insect pests is to keep the lawn healthy. Our natural lawn care services can help keep your lawn healthy.
  • Use slow-release organic fertilizers to reduce the chance of runoff. Read and follow label directions so you don’t use too much fertilizer. Avoid using fertilizer near waterways.

Lawns in the right place

Consider how you use your lawn. Do your children play games on it? Do you like to lie on the grass on sunny afternoons? Or is it just a green swath to look at from your window?

A large expanse of green lawn became popular in America in the 20th century as a way to represent wealth and success. It is reminiscent of the English manor. Is it time to change our perceptions?

Lawns are a monoculture. This reduces biodiversity, especially when the lawn covers a large area. If you would like to have more birds, bees and other wildlife around, you need more plants and less lawn.

We’re not suggesting that you get rid of your lawn. But it is worth considering where it is appropriate to have a lawn.

Lawn size: improving your lawn’s environmental impact

  • Reduce or remove your lawn in shady areas where lawns don’t grow well. Replace it with shade-tolerant ground covers or other plantings.
  • Don’t attempt to grow a lawn on a steep slope or on the shoreline of a stream or lake. Plant native plants in these areas.
  • Consider removing the lawn where it is not used and replacing it with other plantings. They may be more attractive and less work, provide habitat for birds and wildlife, and reduce runoff from your landscape.

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