Landscaping Tips: Salt and pH levels in soil important factors in landscaping

By Kelli Belden, Research associate and director, UW Soil Testing Laboratory

Wyoming soils frequently have high pH measurements and high levels of soluble salts. If a gardener or landscaper chooses plants that do not tolerate the pH or salt levels present in the soil, the plants will not thrive and sometimes will die. A standard soil test will identify either of these conditions. 

The pH is a measure of how acidic or alkaline a soil is – the pH scale runs from 0 (very acid) to 14 (very basic) with 7 considered neutral. Lemon juice, for example, has a pH of about 2, while ammonia has a pH near 11. 

Most plants prefer a pH between 6 and 8. Outside this range, solubilities of essential nutrients change dramatically, and toxicities can occur at the extremes.

Most Wyoming soils have pHs above 7, and some are above 8. The higher pHs are usually due to the presence of free calcium carbonate (lime). Neutralizing lime is difficult to do on a landscape basis and, over time, the soil usually returns to its original pH.

To grow plants that prefer acidic soils, purchase potting mixes formulated for acid-loving plants, and grow them in pots or other decorative containers.  

Salts can come from many sources: the rock from which the soil weathered, dissolved salts in the water, manure, fertilizer applications or salts from applications to roads and sidewalks during snowstorms. High salt levels can cause wilting, leaf burn, stunting, germination failure and nutrient uptake failure. 

Laboratory tests are required to determine if the problem is high salt, high sodium or both.

In general, if the problem is salt and good drainage exists, flush the soil with fresh water and then retest the soil. If access to good water is not available or good drainage cannot be established, choose plants that tolerate salt. Beans, strawberries and roses are sensitive to even moderate levels of salt, but asparagus, beets, squash, fine fescue and tall fescue grass, junipers, pines and evergreens are among the plants relatively tolerant. 

Local University of Wyoming Cooperative Extension Service (UW CES) offices have information on the salt tolerance of many plants (contact information is at http://ces.uwyo.edu/Counties.asp).

Information is also available in the UW CES bulletin B-988, Soil Salinity, Salt Tolerance, and Growth Potential of Horticultural and Landscape Plants, at: http://ces.uwyo.edu/PUBS/Wy988.pdf.

Sodium is a component of some salts and creates special problems in the soil. In addition to causing symptoms similar to high salt, sodium can cause a loss of soil structure (the arrangement of soil particles into aggregates), which can slow water infiltration and movement or even stop it.  Under sodic (high sodium) conditions, the pH often increases to 8.5 or above, and the decay of organic material may be slowed.   

If soil is high in sodium, the treatment becomes more difficult. There are a number of materials – gypsum, sulfur and lime sulfur, for example – that can be used to replace the sodium in the soil. After the material has been allowed to react with the soil, the treated area is leached with water. 

Never begin treatment for a salt or a sodium problem without having the soil tested and consulting with a qualified professional. If treatments are done improperly, soil conditions can become worse. After leaching a saline or a sodic soil, have the soil retested to establish the effectiveness of the process.

Soil testing is a service provided by the UW College of Agriculture.

Soil testing information sheets can be obtained at any UW CES county office or online at http://uwadmnweb.uwyo.edu/RenewableResources/soil/soil_lab.htm.

There is a $20 fee for the standard test, which includes pH, salts, organic matter, phosphate-phosphorus, nitrate-nitrogen, lime and texture. There is a $4 fee for additional tests. The lab can be reached at (307) 766-2135.

Additional UW CES bulletins on gardening and landscaping can be found at http://ces.uwyo.edu/PUBS/Horticulture/Horticulture_Publications_Main.htm.

Contact: Robert Waggener, Editor
Phone: (307) 766-3571
E-mail: robertw@uwyo.edu

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