Lawn Care and Stormwater

Keep your lawn green and the water blue. Using too much fertilizer and other lawn care products can cause water pollution. The same rain that helps turn your lawn green also washes excess fertilizers, pesticides, and other pollutants into the nearest creek, turning the water green, or worse. Much of it makes its way downstream to the Chesapeake Bay. Have your soil tested to determine how much fertilizer you really need. And use lawn care products as instructed on the product labels. Less is always more when it comes to water quality.


Fertilizer is a pollutant when it is washed off lawns and gardens into streams, rivers and other bodies of water. Fertilizer consists of plant nutrients that help plants grow and reproduce. In the water these nutrients feed naturally occurring algae and can lead  to massive algae blooms, particularly during the warm summer months. An algae bloom is an explosion in the algae population that turns the water green, shutting out sunlight needed by bottom-growing plants and leading to oxygen depletion that kills fish, oysters, crabs and other aquatic creatures.

How does Fertilizer Cause Fish Kills?

It might seem strange that an overabundance of plants (algae) can cause a reduction in the amount of oxygen available to other aquatic organisms. There are two ways that algae blooms remove oxygen from the water.

  1. While plants use the energy in sunlight to take in carbon dioxide and give off oxygen during the day, at night plants take in oxygen and give off carbon dioxide. Most fish kills occur in the early morning hours.

  2. The life cycle of individual algae is quite short. During an algae bloom billions of the microscopic organisms die and sink to the bottom, where they begin to decompose as they are consumed by bacteria. Bacteria consume oxygen, adding to the effect described in #1, leading to a severe drop in the amount of oxygen available in the water.

Responsible Use of Fertilizer

The best way to prevent water pollution by fertilizer is to apply no more fertilizer than can actually be used by the plants you are tending.  Some practices which will limit the amount of fertilizer available to be washed into stormdrains and streams are:

  1. Have your soil tested. Based on a soil test, you can apply exactly the kinds and amounts of nutrients that the grass on your lawn needs to grow (any more than that is wasted and is left behind to wash away into local streams).  The Virginia Cooperative Extension Service will test your soil for $7.00. In Albemarle County and the City of Charlottesville the VCE can be contacted at (434) 872-4580.

  2. After having your soil tested, follow the instructions that come with commercial fertilizer to make sure you apply no more than is required.

  3. Apply fertilizer in the fall when it is most beneficial to cool season grasses and least likely to end up in runoff.

  4. In town, avoid leaving fertilizer on hard surfaces such as sidewalks and driveways where they are most likely to be washed into a storm drain, where it will end up in a stream. Sweep fertilizer off hard surfaces onto the lawn or into the garden.

  5. If possible, avoid applying fertilizer just before a rain storm.

Other Lawn Care Products

Much of what applies for fertilizers applies equally well to other lawn care products such as pesticides and weed killers. Follow the instructions which accompany the product and take care not to over apply. Herbicides in the class of RoundUp should be applied on a sunny day, as the harmful components in the product break down very quickly in sunlight. Be very careful not to apply RoundUp and similar herbicides near a stream or pond as the substance does not break down in water and is particularly  harmful to aquatic organisms such as frogs.

Mowing the Lawn

Don't cut your grass too short. Leaving grass at least 2 or 3 inches tall is better for the health of a lawn. Keeping a lawn even longer helps prevent erosion, filters out pollutants that can be washed into storm drains and streams and keeps it healthier during the drier and hotter days of summer. Leaving grass clippings on a lawn reduces the need for fertilizer and reduces the amount of waste disposed of in landfills.

Read Your Weeds: A Simple Guide to Creating a Healthy Lawn Complete with a chart of various weeds that can help you diagnose any  deficiencies affecting your lawn, this pdf document discusses the most common problems and the best way to solve them in an environmentally friendly manner.
A Virginian's Year Around Guide to Lawn Care (3.3 MB) Tips and techniques for healthy gardens. Published by the Department of Conservation and Recreation and the chesapeake Bay Program.

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