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USU Extension Service - Lawn Aeration

Article Date: 
4 March, 2011 - 06:00

Compaction
Healthy roots are the foundation for vigorous, lush plant growth.  Roots need a balanced supply of air, water and nutrients to thrive.  Compaction reduces the volume of pore space in the soil, limiting air exchange, water intake and ultimately roots growth.  Its symptoms include weak, slow-growing plants and thin turf stands.  Compaction is more of a problem on heavy clay soils than light sandy soils.    
While turf is grown to handle a lot of traffic, each occurrence has an additive effect.  Foot traffic, car parking and dog trampling can all contribute to creating compacted soil. The problem is particularly severe when the traffic occurs while the soil is wet.  Winter freezing and thawing along with the aeration provided by worms and decaying roots provides adequate aeration for lawns that receive less traffic.  However, for those lawns that are heavily used, compaction can seriously degrade its health and appearance.
Thatch
Thatch is a layer of fibrous residue that occurs between the soil and the green leaves of the turf.  It consists of dead plant tissue in the process of decomposition.  While some thatch is desirable to insulate the soil, more than a ½ inch is considered detrimental.  Excess thatch inhibits water intake, prevents grasses from rooting into the soil, and can harbor insects and diseases.  Thatch also ties up pesticides that are applied to the soil, making them ineffective.  Compaction, excessive fertilizer or water applications are often the cause of thatch buildup.  These practices create an imbalance that make it difficult for soil decomposition micro-organisms and earthworms to keep up with the production of organic debris.  
De-thatching
When thatch layers are thicker than ½ inch it may be useful to remove some of it.  Using a hand rake, or for larger areas a power rake or vertical mower is often necessary.  De-thatching removes a lot of material, but also may damage the grass. When using de-thatching machines it is important to set the blades high enough to prevent the tines from raking the soil.  Generally machine de-thatching is not recommended.  Instead of removing thatch encourage its decomposition by core-aerating, and leaving the plugs on the lawn to filter down through the grass creating an improved environment for thatch decomposition.  Though the plugs may be unsightly and cause mud to be tracked into the house, their removal is discouraged.
Aerating
Regardless of the reason for compaction or thatch buildup, core-aeration is an effective way of returning balance to the growing system.  This method implements a rolling drum or axle mounted with hollow metal tines to remove cores of soil and thatch from the lawn.  Those with tines that penetrate 3-4 inches into the soil are preferred.  For the most effective aeration, go over the lawn twice in perpendicular directions.  Aeration is particularly beneficial on slopes where water has difficulty penetrating, and in traffic areas that receive more compaction.
When aerating, it is important to have adequate moisture in the soil to allow the tines to penetrate to their full depth.  Lawns can be aerated at any time and as often as needed, as long as the ground isn’t frozen. Grass grows best during the cool weather of spring and fall.  These are the preferred times to aerate. Spring is the time that most people aerate.  However, most weeds germinate in the spring, thus fall aeration is recommended due to a reduced likelihood of weeds invading through the core holes.  
When aerating in the spring, try to have it completed before applying pre-emergent herbicide applications for crabgrass and spurge.  Aerating after a soil applied herbicide treatment can reduce the chemical barrier formed by the herbicide.  
Aeration can solve many of the common problems encountered in high use lawn areas.  If compaction or thatch is a problem for your turf, consider aerating and give the lawn a breath of fresh air.