Lime is arguably the most recognized but least understood substance applied to lawns. Many homeowners know that a certain amount of lime is needed for a healthy lawn. Few, however, realize why, when, or how much should be applied. Lime works to neutralize an acidic soil but is only a temporary measure. In Northern Virginia, our heavy, clay soils will need lime applied on a regular basis to maintain the soil pH in the optimum range for turfgrass growth. An initial soil test should be conducted to determine how much lime is needed to correct your soil and follow up testing should occur every 4-5 years thereafter.
The acidity or alkalinity of soil is described by the pH level. The pH scale ranges from 0 to 14, with low numbers representing acidity and high numbers representing alkalinity. A pH of 7 is considered neutral. The scale is logarithmic as opposed to linear, which means that a pH of 5 is ten times more acid than a pH of 6 and a hundred times more acidic than a pH of 7. Soil pH affects the way nutrients are held in the soil. Correcting acidic soils by applying lime will release many nutrients. For a majority of the nutrients needed by lawns to be readily available, a pH of around 6.5 is best.
The second major problem for lawns growing in soils that are too acidic is poor root growth. Grass roots tend to be stunted and not grow deeply in these conditions. This is thought to be due to aluminum toxicity in lower pH soils.
Lime is not taken up as a nutrient by turf, but has to move through the soil profile to do its job. Lime releases nutrients trapped in acidic soils as it moves down through the root zone of turf. This stimulates more vigorous root growth, increases the impact of future feedings, discourages many weeds, and results in a higher quality lawn overall.
Bio Green suggests applying lime in the winter months. With moisture levels high and frequent freeze and thaw, lime moves more quickly through the root zone than in warmer, drier months. In addition, there is no conflict with fertilizer applications in the winter. Lime should not be applied with nitrogen fertilizer.
Lime is safe to use. The common forms of lime applied to turf (calcite and dolomitic lime) are non-toxic and will not cause pollution problems. Lime is actually applied to many lakes to reverse the effects of acid rain.
The quantity of lime needed varies a great deal from lawn to lawn and from place to place within a lawn. A soil test should be done initially to properly determine the correct amount. Bio Green gets soil test results from Virginia Tech, and these results provide an exact measure of how much lime is necessary for optimal lawn health. Bio Green’s lawn technicians are experienced in customizing lime application for areas within a lawn that are more acidic (within the drip line of trees, poorly drained areas, etc.). For maintaining a neutral pH level in Northern Virginia, a good rule of thumb is to apply 50 lbs of lime per 1000 square feet every 2 years. This should be increased if a lawn is shady, poorly drained, or has a higher than normal clay content.