"Green" lawn care
Thoughtful lawn care and fertilizer use is important to restoring and protecting our waterways.
The same nutrients - phosphorus (P) and nitrogen (N) - that fertilize our lawns, also "fertilize" our river, lakes, ponds and streams. Yet our river, lakes, ponds and streams don't need fertilizing. In fact, the Assabet River and many local streams, lakes and ponds are grossly over-fertilized by nutrients, which come from stormwater runoff and sewage treatment plant discharges. These excess nutrients cause aquatic plants and algae to grow like crazy in the summertime - a condition called eutrophication. This prolific plant and algal growth can ruin our waterways for boating, fishing and swimming and also harm fish and other aquatic life.
How lawns can contribute to the nutrient problem
Lawns are aesthetically pleasing and provide enjoyable places to play and relax. But they can also export significant loads of phosphorus and nitrogen to the rivers, streams, lakes and ponds. How? During a storm, rainwater (aka "stormwater") transports phosphorus and nitrogen attached to fine soil particles, or dissolved in the rainwater, from your yard to nearby waterways. Nitrate, a form of nitrogen that does not bind to soil particles, can also leach down into groundwater, particularly in sandy soils, and eventually enter streams and wetlands. In dry weather, wind can also carry nutrient-laden particles and organic matter from your yard to nearby waterways. In most of our waterways, it is the phosphorus that is the "limiting nutrient" and the one we need to decrease in order to make them healthy again.
The trouble with phosphorus in fertilizer
Most lawns in this region don't need phosphorus fertilizer at all. Most soils naturally have enough phosphorus to support a lawn. The Commonweath's new lawn fertilizer law passed in 2012 recognized this, prohibiting the use of phosphorus-containing fertilizer on lawns unless they are shown to need it. Organic fertilizers are allowed because the nutrients are released more slowly and are less likely to run off into waterways. So test your soil before you fertilize. If you are establishing a new lawn phosphorus fertilizer is allowed because it helps to build strong root systems.
Other sources of nutrients?
Rain and wind also transport phosphorus and nitrogen to waterways from undeveloped and uncultivated lands. Most of these nutrients enter rivers and streams attached to soil particles or contained in organic material such as dead leaves. It is a natural process.
Managing Your Lawn for a Cleaner River
Steps you can take to protect local waterways.
Check the depth and quality of your topsoil. A healthy lawn requires at least 4-6 inches of good topsoil. Deep, healthy soil is the foundation of a healthy, low-maintenance, non-polluting lawn. Adding organic matter such as compost by tilling or top-dressing is an excellent way to improve soil health and texture. In sandy soils, the addition of compost will improve water and nutrient retention; in heavier clay soils, it will improve drainage and aeration. Thoroughly mixing compost into the soil will also enhance and enlarge the root zone for grass plants. This is important for the long-term health of your grass because a deep root system will help grass to weather droughts and other stresses. Ideally, soils should contain about 10% organic matter.
Test your soil
Measure the pH (acidity) of your soil, and the amount of phosphorus and organic matter that it contains. UMass Extension offers low-cost soil tests; soil test results include recommendations for pH and nutrient adjustment. For more information, contact the UMass Soil Testing Lab at (413) 545-2311.
Avoid fertilizers containing phosphorus when possible
Apply only the type and quantity of nutrients your lawn needs, and adjust the soil pH if necessary. Bring your soil test with you when shopping for fertilizer. Garden centers and nurseries in the area that can help you interpret the UMass soil test results and select the right fertilizer for your lawn. Getting the soil acidity (pH) right will ensure that the nutrients in the soil are available to the grass, making it healthier.
Keep fertilizer and water on your lawn where it is needed
Use Slow-Release Fertilizers
Quick-release, water soluble (inorganic) fertilizers become available to plants almost as soon as they are applied to the lawn. The overall effects, however, are short-lived and sometimes harmful to the lawn's long-term health. For example, a water soluble (inorganic) nitrogen fertilizer will produce rapid leaf and shoot growth, but it may also cause excessive leaf and shoot growth, reduced root growth, and leaf burn, making the grass plants more susceptible to drought and disease. Moreover, these water soluble fertilizers are easily washed away by rain. Slow-release, water insoluble (organic) fertilizers produce green lawns without excessive leaf and shoot growth, or the risk of leaf burning. They are designed to provide a steady supply of nitrogen to the grass over a longer time period. And they are less likely to wash off lawns or down into groundwater because they are water insoluble.
What to Look for When Shopping for Fertilizer
Most lawn fertilizers contain a blend of the three major nutrients that plants typically need, nitrogen (N), phosphorus (P) and potassium (K). The amount of each nutrient in the fertilizer is printed on the bag as a ratio of N-P-K, for example, a "2-3-3" fertilizer contains 2% nitrogen (N), 3% phosphorus (P) and 3% potassium (K). Buy fertilizer with a 0 in the middle! In addition to the nutrient ratio, the bag will usually tell you the percent of each nutrient that is water soluble (inorganic) and water insoluble (organic). Go for the water insoluble or "slow-release" fertilizers, which depend on microbial and chemical action in the soil to make nutrients available to plants.
Organic fertilizers are water insoluble, slow-release fertilizers. Many organic fertilizers also contribute organic material and micronutrients to the soil. There are some synthetic (manufactured) slow-release fertilizers available as well. Both water soluble and water insoluble fertilizers ultimately provide grass plants with the same usable forms of nutrients, but the water insoluble fertilizers are less likely to wash away and are longer-lasting sources of nutrients.
Don't Let Your Fertilizer go Down the (Storm) Drain!
Do not fertilize before a heavy rain. The fertilizer will wash off into the street and enter the nearest waterway. Apply only the type and quantity of fertilizer indicated by the soil test, and keep both fertilizer and water on your lawn (and off your driveway) so it won't wash away.
Vegetated Buffer Strips
Maintain a natural vegetated buffer strip between your lawn and your street and driveway to reduce soil erosion and the transport of fertilizer-enriched rainwater from your property. This buffer should be as wide as possible and planted with deep-rooted, shrubs and plants. Consider planting native shrubs and plants as they are well adapted to local soils and climate.
Mow High and Mow Often
Mow your grass 3 inches high or put your mower on its highest setting, and make sure your blades are sharp. Tall, dense grass shades out weeds. Tall grass is usually healthier than short grass because it has deeper roots and more stored sugars, which helps the grass to resist disease, pests, and drought and make more grass plants.
Recycle your grass crop
Leave grass clippings on your lawn. Grass cuttings are a cheap source of slow-release nitrogen fertilizer that adds organic material to your soil. If you prefer to remove grass clippings from your lawn, compost them. Next time you need a mower, consider buying a mulching mower that chops grass into very small pieces. Don't dump grass clippings or other yard waste into wetlands or near ponds, lakes, streams or rivers. As the yard waste decays, rain will wash nutrients from the wastes into waterways.
Water infrequently, but deeply
Water only when needed, but water longer, so that water penetrates deeper into the soil allowing the roots of grasses to grow deeper into the soil. When there is a dry spell, these deeper roots will still be able to feed the grasses. Frequent, short watering causes grasses to grow shallow root systems that become easily stressed during a dry spell. Your lawn usually needs watering when the grass curls and/or when footsteps on the lawn leave visible impressions. Healthy grass will come back as green as ever even when dried to a brown crisp during a drought.
Reduce your lawn area
Replant lawn areas that aren't needed with low-maintenance woodland gardens, flowers or shrubs. Ask yourself, how much lawn do you really want to maintain? There are many alternatives to lawns that require less fertilizer, water and work. They will also enhance your landscape's beauty and natural plant diversity, and attract songbirds, butterflies and other wildlife.