The Dirt on Dirt

By Cynthia Bee, Conservation Garden Park

Most of Utah’s population lives in the former lake bed of ancient Lake Bonneville. As a result, there are a whole host of interesting soil mixes throughout the state.  Some areas are basically sand bars (which creates a certain set of challenges) and other areas have clay soil with varying degrees of rock added to the mix.  Whatever your soil, there are ways to cope.

Legacy of Lake Bonneville

Many thousands of years ago, most of Utah and portions of Idaho and Nevada were covered by an inland sea, called Lake Bonneville.  The former “beaches” of Lake Bonneville (that we now call benches) can be seen along the base of our mountains and represent two different lake levels that occurred over the ages.

As Lake Bonneville dried up, the salts left behind were concentrated into the soil of the lake bed and into the remaining lake (now called the Great Salt Lake).  This means that the ph of our soils is high and some plants, such as blueberries, simply won’t tolerate this alkalinity (salt).  Alkalinity is a condition all Utah soils “enjoy” to varying degrees.

Sandy Soils

Some areas of Utah, especially near canyon washouts and the along the upper benches, are made up of sandy soils.  If you have this soil type, you’ve probably noticed there is no amount of water you can put on your soil that it can’t absorb—and still want more.  Adding thirsty plants, such as lawn, further exacerbates the problem.

The solution for sandy soils is to improve the water holding capacity of the soil through the addition of organic matter.  Ideal soils contain 3-5% organic matter but Utah soils average about 1%.  Organic matter includes composted leaf matter, bark, and manure.  Additionally, choose plants which appreciate sharp drainage and limit the use of lawn and other thirsty plants in these areas. Sandy soils should be watered more frequently but for a shorter time.

Clay Soils

In states where rainfall is plentiful, clay soils can become a boggy, saturated mess that waterlogs plants and creates a host of disease and root issues. As a result, complaints about clay soils can be read in many gardening publications; but their climate is not our climate.

In Utah, the ability of clay soils to hold on to water can be a benefit if you’re watering correctly for conditions.  Because clay soils are slower to absorb water, running the sprinklers too long will cause the water to runoff.  When watering clay soils, set the watering time for each area or zone to half the total needed then run through each zone twice.  This is called the “cycle and soak” method and it ensures the soil can absorb all of the provided water.  Improving the health of clay soils is the same recipe as sandy soil: add organic matter.

If you’re not sure what type of soil you have, USU Extension can provide a soil analysis test for a small fee.  More information on soil testing is available at www.usual.usu.edu. Visit Localscapes.com to find classes and training to help you “localize” your own piece of Utah.

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