Frequency

• Schedule to aerate a lawn at least once a year. Aeration becomes especially important in turf grass grown in clay or heavy loam soils or where water tends to puddle in low spots across the property. When water from rain or the irrigation sprinklers tends to run off and not soak into soil, it may be a sign an aeration is needed. Some types of lawn grass tend to accumulate a thatch atop the soil and prevent water from reaching the topsoil, such as with creeping bentgrass, Kentucky bluegrass and zoysia grass. In conditions when heavy soil, traffic compaction and thatch build-up are all issues, aeration needs to be conducted twice a year.
  
  

Seasonal Timing

• When to aerate depends on the type of turf grass species. Cool-season lawns made up of bluegrass or fescue, for example, are best aerated in the fall when temperatures are cool and soil is moist. Warm-season grasses, such as zoysia grass or St. Augustine grass, benefit from aeration in late spring or early summer when they have greened up. The key is aerating at a time the lawn grass is actively growing and its roots immediately take advantage of the improved conditions. Avoid aerating when the grass type is dormant.
  
  

Aeration Considerations

• The aeration machine looks like a lawn mower but it houses a reel with numerous tube-like metal tines. The topsoil must be moist and easily penetrated by the tines. If the soil is dry, irrigate deeply one to two days in advance of a scheduled aeration. Also, postpone aeration if the soil is mucky as you don't want to slide or further compact the soil. Each tine bores into the soil surface through the lawn grasses and pulls up 2 to 3 inch long by 3/4 inch wide plugs that rest on the lawn surface. These visible plugs slowly crumble away over several weeks.
  
  

Caveats

• When aerating in fall, do it at least 30 days before the expected first frost date. This allows ample time for the grass roots to recover and grow healthy before the stresses of subfreezing temperatures. If you miss the timing of aeration of a cool season lawn in the fall, the next best time is in early spring. For warm-season grass lawns, only aerate when the lawn is green and avoid fall aeration unless you live in a frost-free winter climate.