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.
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
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.
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.
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.
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
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
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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