August 21, 2002

Cultivate your soil for a healthy lawn

By Stanley Moore
Special to the Herald
       In compacted soil, the soil particles are packed so tightly together that air is driven out, water can't drain through and plant roots can't easily penetrate it. In a lawn, this translates into shallow rooting and poor turf health, and it could eventually result in fertilizer runoff into surface water.
      "Compaction problems are most severe in fine-textured soils - those with a high clay content," said Ron Calhoun, Extension turfgrass specialist at Michigan State University. "Sandy soils resist compacting, but high foot or vehicle traffic on any soil, especially when it's wet, can push soil particles together."
      Several types of cultivation tools are used to physically modify the soil, either by removing small cores of soil or slicing or pushing holes into it. Research has shown that machines that pull soil cores are more effective, Calhoun noted.
      In either case, the closer the tines are spaced, the more soil is affected and the better the results.
      "Deeper is better, too," he said, "especially if a thick thatch layer is present."
      Thatch, an accumulation of dead and decomposing grass stems, leaves and roots between the soil surface and the green top growth, is beneficial when it's « inch thick or less because it allows air and water through but protects grass plants against weather extremes and discourages weed seed germination by shading the soil.
      Thatch that builds up more than 1 inch, on the other hand, acts as a barrier to water and air movement. Compacted soils and overwatering encourage thatch formation, Calhoun said, so often compaction and thatch problems occur together.
      Deep cultivation - at least 2 « inches - gets past the thatch layer and deeper into the soil. If the thatch layer is 1« inches and the cultivation machine has tines only 2 inches long, they will barely nick the surface.
      "The homeowner may feel better for having run the machine over the lawn, but the activity won't have much impact on the turf," Calhoun observed.
      The typical bluegrass lawn tends to accumulate thatch more quickly than lawns composed of other types of turfgrass, and two or more cultivations a year may be needed for best results. Once the thickness of the thatch layer is reduced to less than a 1 inch, annual cultivations may be adequate.
      Other factors are the type of soil (sandy vs. clay), the degree of soil compaction, the use of the turf, and the homeowner's goals for the lawn and willingness to commit time, money and effort to maintaining it.
      Fall and spring are the best times to cultivate, Calhoun said, because lawns are growing vigorously then and will quickly recover from the process.
      Avoid cultivating when the soil is either very dry or very wet, he advises. Tines will not penetrate dry soil, especially dry clay soil, well. Cultivating when the soil is wet may cause unnecessary injury to the turf.
      After cultivation is a good time to seed bare or thin spots, he noted.
      For more information, call Stanley Moore, MSU CED Antrim County at (231) 533-8818, fax(231) 533-8392 or e-mail: moores@msue.msu.edu