Top Soil
September 2016
Carver County Water Management Org. Water Column
Soil is easy to take for granted. Our daily interactions with it and our luck at having good soil in
Minnesota allow us to forget how we very much depend on it to grow our food, filter our water,
support our infrastructure and more.
It is one of the most precious and wasted resources we have.
Soil & top soil
Soil covers the earth’s surface and is made up of minerals, organic matter (plant and animal
matter), air and water. Soil has layers; each with different compositions and purposes. The top
most layer is called top soil. It’s usually about 6-12 inches deep, dark in color, rich in organic
matter, and full of plant, animal and microbial life. Top soil provides benefits that only it can
including;
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Providing a place for plants to grow with all the necessities plants need.
Saving drinking water. In a healthy top soil, plants can grow long roots to reach water
and the soil actually holds on to more water because of the water retaining organic
matter. Thus, watering and irrigation systems aren’t often needed, even in dry periods.
Reducing runoff. Keeping water on lawns decreases pollutants in our lakes and rivers
and creates less flooding.
Happy homeowners. Good top soil is necessary for healthy lawns and gardens.
Our losses
Too often when development occurs, top soil is lost. When mass re-grading of the landscape
occurs, top soil is often scraped off and mixed with less rich soil layers below it. Sod placed on
the now mixed and, often compacted soil, cannot survive well. The roots can’t break through the
compacted soil and thus can’t find water or nutrients. Homeowners must frequently water to
keep the grass alive. More watering leads to more water runoff since the water can’t soak in
past the grass to the compacted soil below. Runoff causes pollution in lakes and rivers.
Requirements
The Carver County Water Management Organization has “water rules” in place to protect lakes
and rivers from pollutants resulting from development. Our organization is seeking to improve
our rules by amending the top soil requirements for new developments. When regrading and
changing the landscape, developers will now be required to have a top soil management plan to
save the top soil on their site, and must ensure that at least 6” of top soil gets placed back on
the site before sod or seed is put down.
What can homeowners do?
When buying a new home, ensure that the developer/builder places adequate top soil back on
the property. At least 6 inches are required. If the top soil isn’t black it is likely to be low quality.
If you already have a home lawn there are some things you can do:
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Check for soil compaction using a wire flag. If you can’t easily push the wire into the
lawn more than three inches, you have compaction. Core-plug aeration can reduce
compaction and the fall is the best time to do this.
Test for organic matter. Organic matter makes soil black and crumbly. If the soil beneath
the lawn looks gray or tan, there is little organic matter. Use the University of Minnesota
Soil Testing Lab by sending in a sample to know for sure. To add organic matter, spread
a thin layer of compost on top of the lawn. Again, fall is best for this.
If your soil has a lot of compaction, you might consider tilling up the yard and adding in
larger amounts of compost to increase organic matter to healthy levels. When reseeding, consider trying out “Fine-Fescue Lawn Seed Mix” – fine-fescues have much
deeper roots than Kentucky Bluegrass, marking them more drought tolerant, and they
also don’t need frequent mowing.