Got Nature? Blog

Purdue Landscape Report: PART 1 – The Importance of “Physical” Soil Testing
In my 40 years of teaching and consulting, one of the biggest and most frustrating problems I continually encounter is when so called “landscape professionals” and homeowners continue to apply annual soil fertilizers, lime, and other soil amendments without ever conducting a professional soils test.

Before planting long-lived trees, shrubs, flowering perennials and lawns, it is absolutely essential to have your soil tested for its physical, chemical, and biological properties. To have a beautiful landscape, an awesome lawn, or a very productive vegetable garden, we need to do soil tests because the health and vigor of everything we grow is directly dependent on the soil we are growing our plant’s roots in.

Figure 2: It is important to recognize the amount of sand, silt and clay in your landscape soils.

Figure1: A soil probe can be useful for soil testing and checking for moisture in the soil.

As an analogy, when you go to a family doctor or physician, why will they usually require a professional blood test from you?  They want to “show you the numbers” of your cholesterol, HDL, LDL, triglycerides, sodium, potassium, and a whole array of other very important blood tests. Again, if they prescribe you to take medications, but they are not helping and can actually hinder your health, lawsuits can definitely occur. I tell my students, before anything is applied on a client’s property, “show me the numbers”!

Although many intelligent homeowners and landscapers may have initially done a chemical soil test, many have never done a soil texture, soil compaction, and/or soil drainage test on their property or their clients. Why do we need to do these “physical” soil tests?  Think about it. For root growth, its not just about nutrient deficiencies, toxicities, or soil acidity problems, its about life giving oxygen in the root zone. Without oxygen, the entire ecosystem below ground will suffer. This is why I recommend you to determine your soil texture, (sand, silt, and clay %’s). Professional soils labs can determine your soil’s texture and that is very important, not only for knowing how much and when to water, but to determine what kind of fertilizers will work best for your soil. Many sandy soils are nutrient deficient because they have little negatively charged organic matter or clay to hold onto the positively charged nutrient fertilizers (cations). Excess rain and watering will leach many of the quick-release fertilizers, especially nitrate and potassium out of the root zone. This is why I recommend slow-release fertilizers on most soils so your plant’s roots will have available nutrients for a much longer time.

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Resources
Soil Sampling Guidelines, The Education Store, Purdue Extension resource center
Soil Testing for Lawns, The Education Store
Consumer Horticulture: Collecting Soil Samples for Testing, The Education Store
Certified Soil Testing Laboratories, Purdue Extension – Master Gardener Program
Example soil test form

Chris Carlson, Associate Professor
Kent State University Arboriculture & Urban Forestry