Soil Testing

Pulling a soil sample and sending it to a soil lab is a key first step in achieving better lawn and garden results!

Soil cores from a home lawn can be sent to a soil lab once organic debris is removed and they are allowed to dry. Soil test results from a lab can take several weeks, so plan ahead.

Soil cores from a home lawn can be sent to a soil lab once organic debris is removed and they are allowed to dry. Soil test results from a lab can take several weeks, so plan ahead.

BEGINNING WITH THE FUNDAMENTALS

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 planting and renovating lawns, we always used the soil testing services of the Merkle Lab at Penn State, mailing soil samples to 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 those levels in lawns, gardens and landscape beds.

For Do-It-Yourselfers, soil test kits were available for $12 (in 2011) from Penn State Extension offices. Check the agricultural extension office in your state for soil test kits, or order a soil test kit here.

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


Crop specific soil test results from the Merkle Lab at Penn State provide recommendations for adjusting soil pH and plant nutrients.

Crop specific soil test results from the Merkle Lab at Penn State provide recommendations for adjusting soil pH and plant nutrients.

The soil test results above show 3 important sections:

  • 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.
  • 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")
  • 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 soil's ability to hold nutrients.
  • SUMMARY - This established home lawn isn't in need of any corrective applications at this time. Therefore, 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)  Soils in regions that get a good bit of rainfall tend to revert back to an acid condition, so they should be retested at least every 5 years.

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 T-handled soil sampler (buy one here) 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 postal shipment to the soil lab. Results follow in 3 to 4 weeks.

You should repeat soil tests every 5 years. 


INTERPRETING SOIL TEST RESULTS

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

  • 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.
  • 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 blossoms.
  • Potash - Another major nutrient that needs to be optimized for the best growth from turf, flowers and woody ornamentals. Often used in fall lawn fertilizers to help the winter hardiness of turf.

HOW TO CORRECT SOIL DEFICIENCIES

Depending how much lime is required to raise soil pH into the best range for your specific crop, it may be necessary to split the amount into two applications.  It is best not to apply more than 50 lbs. of agricultural lime (calcium carbonate) per 1,000 square feet per year.  While fall is often the recommended time for lime applications, we successfully applied non-burning pelletized lime year round (pelletized lime is more expensive than lime powder but much easier and less-messy to apply).

Ideally, you should separate lime applications from fertilizer applications by a couple weeks, and don't pull soil samples close to any lawn applications since it will influence the soil test results.

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) if permitted in your state. Phosphorus fertilizers have been restricted and banned in some states due to environmental concerns for waterways like the Chesapeake Bay.

CAUTION should be exercised when applying potash products (potassium is the last number on a fertilizer label as in 10-10-10) since they have a high salt index and can burn foliage!  You might also be able to find a "lawn winterizer" fertilizer that is high in potash and will help correct a potash deficiency indicated by a soil test.


ALWAYS READ THE LABEL on a fertilizer bag for specific instructions on its proper use!