What is Aeration?
Technically speaking, aeration is the naturally occurring process of air exchange between the soil and its surrounding atmosphere. Practically speaking, aeration is the process of mechanically removing small plugs of thatch and soil from the lawn to improve soil aeration. Textbooks often refer to the practices of soil aeration as soil cultivation (coring, spiking and slicking). The aeration process is also commonly called core aeration in the lawn service industry, and homeowners often refer to it as aeration.

The type of aeratioin euipment used influences the benefits obtained from aeration. Equipment with hollow tines removes soil cores. Equipment with open tines divots the soil surface. Aeration equipment varies in tine size up to 3/4 inch and in depth of penetration up to 3 inches, depending on the manufacture's specification.

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

A 3/4" aeration tine with 6" spacing and a penetrating depth of 3" removes about 1.2 percent of the soil's volume in the 3" profile. The closer tine placement removes more soil, exposes more soil surface area for water and fertilizer uptake, and it alleviates compaction quicker than the wider tine spacing.

Why is aeration necessary?
In most home lawns, the natural soil has been seriously disturbed by the building process. Fertile topsoil may have been removed or buried during excavation of the basement 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 may readily grow.

Compaction is greater on heavy clay soils than on sandy soil, and it is greatest in the upper 1 to 1 1/2" of soil. Aeration helps heavily used lawns and 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 accumlation of more than 1/2" on Kentucky bluegrass lawns impeded 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 freqent 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 aeratioin is benefical 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 turf grass such as Kentucky bluegrass and perennial ryegrass. In most cases, spring aeration is performed between March and May, depending on the locations, turf grass species, and intensity of us. 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 green up and growth.

It is best to aerate warm season turf grasses such as zoysia grass and Bermuda grass 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 green up. It is best not to aerate warm season lawns until they have received their first mowing in spring.

Although aeration is beneficial for lawns, it also can open up spaces for weeds such as crabgrass and annual blugrass to invade the lawn.It is best to aerate before you apply pre-emergence herbicides, rather than after. Aerating after a herbicide aplication can reduce the chemical barrier formed by the herbicide, thereby allowing some weeds to germinate and grow into the lawn. Applying fertilizer after helps the lawn compete against weeds. Water the lawn 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 aerification holes will be filled with white, actively growing roots. These roots are a sign that the turf grass is responding to the additional oxygen, moisture and nutrients in the soil 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 watering, 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 helathier, more vigorous, easier to maintain and have fewer problems than lawns that are neglected.

Technical credit: This material was taken from a brochure written by Dr. Robert Shearman, turfgrass professor at the University of Nebraska, Lincoln, NE. The brochure, E258050, is copyrighted by Ransomes Corporation, 1996. All rights reserved.

Thatching:
Not all lawns need thatching. Thatching should be done when there is an excess layer of thatch in a lawn. This can be inspected by cutting a slit in the soil and lifting an edge of the sod along the slit. By looking at the sod from the side- you can see the thatch build-up laying on the surface within the grass. If this layer is over 1/2 an inch- your lawn may benefit from thatching.

Why?
Thatch build-up can starve a lawn from blocking the root systems ability to receive fertilizer, water, and other necessities it needs. Often time, a lawn with excess thatch will not benefit from fertilizer and will brown quickly during drought conditions. Fight back - save the grass- remove that thatch today!

Other uses for thatching (power raking)-
Often, power raking can be done as a spring clean-up approach to lawn maintenance. Hand raking a lawn can be time consuming and tedious. Using a power rake merely speeds up the process. However, the depth of the machine should not be very deep when using the machine, or lawn damage can result.

Click here to find out more about thatching and its benefits