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The Groundwork


Soil and roots are literally the foundation of your turf, and you know you can't build something on top of nothing. Four main issues to consider when caring for soil and grass roots are fertilization, drainage, aeration, and thatch control.

FertilizationAlternatives to grass
Fertilizing your lawn is similar to eating a balanced diet. If your diet has more vitamin C than your body can use, a vitamin C supplement will just wash right through you. The same is true for your lawn; if you apply a fertilizer blend with phosphorus and the supply in your soil is already adequate, the additional phosphorus will wash off into Lake Whatcom. Excess phosphorus causes environmental problems like algae blooms that use up oxygen sources for fish.

Having the soil tested before applying fertilizer is strongly recommended. This will help you figure out which nutrients need to be added and, just as importantly, which ones don't.

The three main nutrients in fertilizers are nitrogen, phosphorus, and potassium. Fertilizer packages indicate the ratio of these nutrients with the proportion of nitrogen listed first, phosphorus second, and potassium last (N-P-K). For lawns, look for blends with a ratio equivalent to 2-0-1 (8-0-4, 16-0-8, and so on) since this ratio is what most lawns in the Lake Whatcom watershed need. Washington State University (WSU) turf and soil researchers agree that almost no lawns around Lake Whatcom need additional phosphorus.
The nutrient ratio numbers indicate the percentage by weight of each nutrient. For example, a 50-pound bag of 16-0-8 fertilizer contains 16% (8 pounds) nitrogen, 0% phosphorus, and 8% (4 pounds) potassium. Ingredients called "carriers" make up the remaining 38 pounds.

Be sure to purchase slow-release fertilizers that have at least 50% slow release nitrogen, to reduce the chance of unused nitrogen getting washed away by rain. Organic fertilizers are usually slow-release, but they tend to have a higher ratio of phosphorus than is needed to sustain turf, which can lead to problems if it washes off into the lake.

If you usually leave grass clippings on the lawn, fertilizing once between late September and late November is adequate. Otherwise, two applications are suggested, once in spring and once in autumn. A maximum of 4 pounds of nitrogen per 1,000 square feet should be applied each year.

A key component to responsible fertilizing is proper timing of applications. The soil should be moist, but don't fertilize during a heavy rain.

The Lake Whatcom Blend, a new phosphorus-free fertilizer mixed especially for Lake Whatcom watershed lawns and based on recommendations from WSU scientists, is now in local stores.

Drainage
Good drainage will foster deep, healthy root growth that is essential for a vigorous lawn. Drainage problems can result from heavy clay soils. Adding organic materials such as compost or peat moss will improve the texture. Sandy soils will better hold water and nutrients, reducing the amount and frequency of fertilization applications. Clay soils will become better aerated, improving infiltration and decreasing runoff. It takes time to build soil structure in a clay soil, so be patient.
Another alternative is landscaping with plants that are suited to your existing soil, rather than altering the site.

Aeration
Soil can become compacted by heavy use, preventing water, nutrients, and oxygen from reaching roots. Aerating your lawn, or loosening soil by removing cores of soil and roots, improves the infiltration of water and nutrients. It also allows much needed oxygen into the soil, stimulating deep root growth.
When aerating your lawn, make sure the soil is moist, but not saturated. Aeration should be done once every year or two. Power aeration tools are recommended because of their excellent results, but non-power tools are available. Leave cores on the soil since they will break down into needed nutrients.

Thatch Control
Another way to improve water movement through turf and soil is to remove thatch, the matrix of grass stems that builds up on the soil surface. Thatch prevents the flow of water and nutrients through the soil to grass roots and harbors pests. Removal of thatch should be done every few years, during late winter or early spring, using rented equipment or by hiring a professional. Proper fertilizing, mowing, and watering will help limit thatch build up.

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Lake Whatcom Cooperative ManagementWSU Whatcom CountyWhatcom County IPM
For more information, contact Scarlet Tang or Todd Murray
WSU Cooperative Extension (360) 676-6736
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