Most people have heard of pH, which refers to whether something is acidic or alkaline. But did you know that your soil’s pH level can dramatically affect the health (and, consequently, the look) of your turfgrass?
For a basic understanding, pH is an abbreviation of the “power of hydrogen” — the “p” is short for potenz (the German word for power), and the H is the element symbol for hydrogen. pH values range from 0 to 14. Determined by a soil test, a particular soil is classified as neutral (about 7.0 pH, which is the pH level of pure water), acidic (below 7.0 pH) or alkaline (above 7.0 pH). For every whole point drop in pH, there is a 10-fold increase in acidity. So, a soil with a 6.0 pH is ten times more acidic than a soil that is 7.0 pH.
The importance of soil pH
So, how does pH affect the health of your turfgrass? Simply put, any soil that is more than slightly acidic makes many important plant macronutrients unavailable for the grass to use them. A highly acidic soil, for instance, makes phosphorus, calcium and magnesium chemically insoluble in water (through which plants take up nutrients from the soil). It can also create toxic soil levels of aluminum, manganese and iron, and it can make many herbicides less effective against weeds.
Alternatively, a soil that is alkaline can make certain key micronutrients (such as zinc) less available to the grass. The presence of common plantain (Plantago major), a broadleaf weed, in your lawn may be an indication of soil alkalinity.
For turfgrasses, the most nutrients are available to turfgrasses when the soil is slightly acidic, between about 5.8 and 6.5 pH (the exception to this is that a centipedegrass lawn does best at a pH level of about 5.5). Unfortunately, many soils become increasingly acidic over time, due to the natural breakdown of organic matter, such as thatch. Soil acidification is also accelerated by the application of nitrogen fertilization, which is typically necessary for the best turfgrass performance. In fact, the most common turfgrass fertility problem in our region is soil that is too acidic.
The only way to know the pH level of your turfgrass site is through a soil test. Soil-test boxes and instructions can be picked up at your local Extension Office. Test results will tell you what your soil’s pH is, and they will make recommendations for both lime and fertilizer for the type of grass in your lawn.
The value of lime
Thankfully, the solution to lowering the pH level of a soil that is too acidic is easy — apply lime, based on your soil-test recommendations. The most common material used for liming is agricultural limestone (ground to a powder), which can be purchased at most farm-supply and garden stores. A lime application should suitably reduce the acid in your soil for two to three years.
Alternatively, if your soil test indicates that your soil is too alkaline, an application of sulfur may be needed. Again, rely on your soil-test results to determine how much sulfur may been needed.
When to lime
Late fall/winter is actually one of the best times to apply lime (or sulfur) to turfgrass for several reasons. First, the normal freezing and thawing of the ground during winter helps incorporate the lime down into the soil. Also, the typically more gentle rains (and the slow melting of snow) reduce the chances of the lime running off and, instead, facilitate the lime moving down. Another good time to apply lime is when you aerate your site.
Actually, any time of year is suitable for liming, but doing so now will allow the lime to penetrate down into your soil, helping neutralize excess acidity, in time for the best spring performance of your turfgrass.