Dieting your lawn

Your lawn’s out of shape! MPAC’s Ryan Anderson constructs a workout and diet plan for your lawn with help from a soil test.

We need to manage our lawn’s soil similar to how one approaches a diet. The best dieters do their research beforehand by weighing themselves, tracking their eating and exercise schedule from weeks previously, and even getting a doctor’s check-up to learn cholesterol levels, blood pressure, and other nutrients in their body.

Think of these dieters as role models for how to transition your lawn to a natural lawn care approach. Like the best dieters, you need to devote adequate time in assessing and understanding the initial state of your soil before acting on it.  You need a soil test.

Hardware stores, universities, and companies all offer soil test kits and/or services. From these tests, focus on the following soil characteristics:

Nutrients: You probably know the big three of nitrogen, phosphorous, and potassium. But, did you know plants require 18 nutrients for healthy growth? Comprehensive soil tests will not only measure phosphorous and potassium levels, but, also, secondary and micronutrient levels such as calcium and magnesium. Soil tests tend to not measure nitrogen since this nutrient is water-soluble, unlike phosphorous and potassium, causing its soil presence to change frequently.  Thus, nitrogen results from one soil test in spring may change in just one growing season.

pH: Soil pH directly affects nutrient availability to grass and other life.  Most grasses excel in a pH range between 5.5 and 6.5.  Turf managers most commonly use some form of lime to raise the pH of highly acidic soils.

Organic matter content: Organic matter or decomposing plant and animal material adds more to your grass than arguably any other product or material.  Leaves, grass clippings, and compost mixed into your lawn slowly changes into dark, nutrient packed humus that retains soil moisture, reduces soil compaction, facilitates cation exchange capacity to hold more nutrients, and improves the habitat for beneficial organisms such as earthworms.  You want to achieve an organic matter percentage between 3 to 4 percent in your lawn.

Soil texture: Soil consists of organic matter, air and water, and mineral particles. Mineral particles of sand, silt, and clay primarily determines the texture of your lawn’s soil.  Soil with too much clay will not drain well and harden when dry. Meanwhile, very sandy soils can drain too much and not retain nutrients very well.  You cannot change a soil’s texture by simply adding more minerals, unless you dig up the entire lawn and switch with new soil.  You can, however, improve the soil structure by adding organic matter to rearrange the individual soil particles.

Do all tests provide information for these four soil characteristics? No! I know the temptation to purchase the cheap $10 to $20 soil test kits at your local hardware store. Unfortunately, these tests both avoid testing for organic matter and soil texture and vary in accuracy and reliability.

For the most (and most accurate) information on all four characteristics, I recommend using a professional lab.  Many university extensions provide lists of soil test providers in your state including the University of Illinois Extension for the State of Illinois.  Professional lab soil tests can cost from $25 to $100 depending on the services asked. The most helpful soil test providers offer recommendations for feeding and managing your soil if the test finds deficiencies in any of the aforementioned soil characteristics.  Just ensure that the provider can give recommendations for lawns, as some providers only perform tests for agricultural crops.

This Michigan State University Extension Home Lawn and Garden Soil Test factsheet describes how most labs conduct soil tests.  MPAC recommends conducting a comprehensive soil test once every three years.

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