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SOIL TESTING


Taking a soil sample and sending it to a soil lab is a fundamental first step in achieving better gardening results!


When you really get serious about growing a nicer lawn, flower bed, vegetable garden or landscape beds, a soil test will be at the top of your priority list. Adjusting soil pH and balancing nutrients before planting makes good sense, especially since some fertilizer is best incorporated into the soil with a rototiller prior to planting. During the decades we were landscaping we always used the soil testing services of the Merkle Lab at Penn State, mailing soil samples into the lab several weeks before we needed the results.


SOIL TEST RESULTS

Soil test results include basic deficiencies and what steps are recommended to correct them in gardens, lawns and landscape beds. 
    
For Do-It-Yourselfers, soil test kits were available for $12 in 2011 from the local Penn State Extension offices. In western Pennsylvania, there's an Extension Office in Washington, PA and another in Pittsburgh (you'll find their contact information at the bottom of this page). 

soil plugs from lawn aeration
Soil sampling 'plugs' sent to the soil lab should be longer than the ones pictured above, 4-inches is about right for lawn soil samples. Soil should be dry and have stones and organic debris removed prior to mailing to the soil lab.


HOW TO TAKE A SOIL SAMPLE

Instructions included with the soil test kit point out that it's important to get a representative sampling of the growing area.  If there are drastically different types of areas, you should send more than one soil sample to the soil lab. 
  
When testing a home lawn, we use a commercial soil probe, which pulls a soil "plug" approximately one-inch in diameter. These soil cores are taken from 10 to 20 locations in your landscape or lawn, allowed to air-dry, then mixed together and packed for shipment to the soil lab. 
  
Results follow in 3 to 4 weeks when we receive your soil test report back from the Soil Lab. At that time, we can provide cost estimates and timing for addressing any soil deficiencies. 
   
Repeat soil testing every 3 to 5 years. 


  


INTERPRETING SOIL TEST RESULTS

There are three major areas we focus on in the report:

  1. Soil pH - This determines if lime needs to be applied, and if so, how much. We also check the Mg/Ca levels to determine what type of lime would be best - calcitic or dolomitic. (also see Soil pH)

  2. Phosphorus - Soils in S.W. Pennsylvania are often low in Phosphorus, and it is critical to have this major nutrient at its optimum level when establishing new turfgrass, or hoping for the best flower blooms.

  3. Potash - Another major nutrient that needs to be optimized for the best growth from turf, flowers or woody ornamentals. (also see Fertilizers)


HOW TO CORRECT SOIL DEFICIENCIES

Depending how much lime is required, it may be necessary to split the amount into two applications.  It is best not to apply more than 50 lbs. of calcium carbonate per 1,000 square feet per year.  While fall is often the recommended time for applications, we successfully apply our pelletized lime all year.

Phosphorus and potassium deficiencies can be corrected with an application of 0-20-20, or separate products like 0-20-0 or 0-46-0 (for phosphorus) and 0-0-60 (for potash). 

CAUTION should be exercised when applying potash products, since they have a high salt index and can burn foliage!  You might also find a "winterizer" fertilizer that is high in potash and will help correct a deficiency.  ALWAYS READ THE LABEL on the fertilizer bag for specific instructions on its proper use.


 


Sample of a soil test report from Merkle Lab
(click image to enlarge)

Soil test results

Agricultural Analytical Services
Laboratory at Penn State

   
This soil test report shows 3 important sections:

  1. Soil Nutrient Levels - The bar graph (with "X's" extending across the page) shows Soil pH, Phosphate, Potash, Magnesium and Calcium levels.  In this particular report, all the levels are within the "optimum range", except for Calcium which is just into the "excessive" range.

  2. Recommendations for: Maintain Home Lawn - This middle section provides specific recommendations for applications.  (The report would be slightly different if you had marked "Establish new lawn" instead of "Maintain home lawn")

  3. Laboratory Results - These are the specific numbers that were translated in the bar graph above.  An additional number of interest is "CEC" (cation exchange capacity) which indicates the soils ability to hold nutrients.


SUMMARY

This established home lawn in Upper St. Clair township isn't in need of any corrective applications at this time.

If someone had "guessed" and applied lime, the calcium level would have been pushed further into the excessive range, and the pH would have become too alkaline. (The pH is currently 7.4, and would ideally be 6.5 to 7.2)

Natural rainfall in the Pittsburgh area will lower this pH into the optimum range within a few years.  Therefore, other than ordinary lawn fertilization, the next thing this lawn will need nutrient-wise, is another soil test in 2004.


MORE

Soil amendments       Fertilizers

Lime application       Science of Soil

Soil pH

   


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