Turf Cultivation and Dethatching

Cultivating turf presents problems that are not encoun-tered in annual crops. Turf is a perennial cover, and you must take special care to prevent undue disruption of its surface characteristics when you need to alleviate a soil problem that occurs in it. Unlike row crops that you can plow, you want to keep your desirable turf intact while cultivating. Manufacturers have developed special techniques and equipment to do so.

Technically speaking, aeration is the naturally occurring process of air exchange between the soil and its surrounding atmosphere. Practically speaking, aeration —also called aerification—is the process of mechanically removing small plugs of thatch and soil from a turf area to improve soil aeration. Textbooks often refer to the practice of soil aeration as soil cultivation (coring, spiking and slicing). The aeration process is also commonly called core aeration or simply aeration.

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WHAT ARE THE BENEFITS OF AERATION?
Core aeration helps the lawn’s health and vigor, and it reduces maintenance requirements. The following are other benefits of core aeration:

  • Improved air exchange between the soil and atmosphere
  • Enhanced soil-water uptake
  • Improved fertilizer uptake and use
  • Reduced water runoff and puddling
  • Improved turfgrass rooting
  • Reduced soil compaction
  • Enhanced heat- and drought-stress tolerance
  • Improved resiliency and cushioning
  • Enhanced thatch breakdown.

The type of aeration equipment you use influences the benefits you’ll obtain from aeration. Equipment with hollow tines removes soil cores. Equipment with open, or solid, tines divots the soil surface.

Aeration equipment varies in tine size up to 0.75 inch and in depth of penetration up to 3 inches, depending on the manufacturer’s specifications. Deep-tine aerators that penetrate much deeper also are available.

Penetration depth depends on soil type, soil moisture, tine diameter, and the weight and power of the aerator. For example, tines penetrate sandy soils easier than they penetrate heavy clay soils, and penetration is better in moist soils than dry soils. In general, turf responds best when cores are close together and deep.

A 0.75-inch aeration tine with 6-inch spacing and a penetrating depth of 3 inches removes about 1.2 percent of the soil’s volume in that 3-inch profile. The same tine spaced 2 inches apart removes about 10 percent of the soil in the same 3-inch profile. The closer tine placement removes more soil, exposes more soil surface area for water and fertilizer uptake and alleviates compaction quicker than the wider tine spacing.

WHY IS AERATION NECESSARY?
In landscaped areas, the natural soil has been seriously disturbed by the building process. Fertile topsoil may have been removed or buried during excavation of basements or footings, leaving subsoil that is more compact, higher in clay content and less desirable for healthy lawn growth. These lawns need aeration to improve the depth and extent of turfgrass rooting and to improve fertilizer and water use.

Intensively used lawns are exposed to stress from traffic injury. Walking, playing and mowing are forms of traffic that compact soil and stress lawns. Raindrops and irrigation increase soil density by compacting soil particles and reducing large air spaces where roots readily grow.

Compaction is greater on heavy clay soils than on sandy soils, and it is greatest in the upper 1 to 1.5 inches of soil. Aeration helps heavily used lawns growing on compacted soils by improving the depth and extent of turfgrass rooting, allowing better water uptake, enhancing fertilizer use and speeding up thatch breakdown.

Most home lawns are subject to thatch accumulation. If thatch is left unmanaged, it can lead to serious maintenance and pest problems. For example, thatch accumulation of more than 0.5 inch on Kentucky bluegrass lawns impedes water, fertilizer and pesticide effectiveness. Core aeration reduces thatch accumulation, minimizes its buildup and modifies its makeup by incorporating soil into the thatch. As soil is combined with the thatch debris, soil organisms are better able to break down the thatch and reduce its accumulation.

Thatch accumulates faster on compacted soils, heavy clay soils and subsoils that are disturbed during building processes than on well-aerated soils. Therefore, lawns require frequent aeration to prevent thatch buildup. Most home lawns growing on heavy clay or highly compacted soils require annual aeration to restrict thatch accumulation.

WHEN SHOULD LAWNS BE AERATED?
Annual aeration is beneficial for most lawns. Lawns growing on heavy clay or subsoils, and lawns exposed to intense use benefit from more than one aeration each year. In general, benefits from core aeration increase when tine spacing is closer and penetration is deeper. Most turfgrasses respond favorably to aeration when it is properly timed.

Both spring and fall are ideal times to aerate cool-season turfgrasses such as Kentucky bluegrass and perennial ryegrass. In most cases, spring aeration is performed between March and May, depending on the location, turfgrass species and intensity of use. Fall aeration is done in late summer and early fall, usually between August and November. Aeration before or at the time of late-season fertilization enhances root growth responses and improves spring greenup and growth.

It is best to aerate warm-season turfgrasses such as zoysiagrass and bermudagrass in mid-spring to summer. Avoid aerating when warm-season grasses are dormant. This may encourage cool-season weed competition. In addition, avoid aerating warm-season grasses during spring greenup. It is best not to aerate warm-season lawns until after they have received their first mowing in spring.

Turf authorities used to advocate that it is best to aerate before you apply pre-emergence herbicides, rather than after. They thought that aerating after an herbicide application would reduce the chemical barrier formed by the herbicide, thereby allowing weeds to germinate and grow in the lawn. Current research, however, disputes this.

Applying fertilizer after aeration helps the lawn compete against weeds. Water the lawn carefully after aeration, particularly in areas where drought and high temperatures are common.

WHAT CAN YOU EXPECT?
Immediately after aeration, your lawn will be dotted with small plugs pulled from the soil. Within a week or two, these plugs of thatch and soil break apart and disappear into the lawn.

About 7 to 10 days after aeration, the holes will fill with white, actively growing roots. These roots are a sign that the turfgrass is responding to the improved soil oxygen, moisture and nutrients derived from the aeration process.

On compacted soils and on lawns with slopes, you should see an immediate difference in water puddling and runoff after irrigation or rainfall. After aeration, your lawn should be able to go longer between waterings, without showing signs of wilt. With repeat aerations over time, your lawn will show enhanced heat and drought stress tolerance.

Don’t expect miracles from a single aeration, particularly on lawns growing on extremely poor soils. Most lawns benefit from annual aeration. Lawns that receive this care will be healthier, more vigorous, easier to maintain and have fewer pest problems than lawns that are neglected.

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