Fall is a great time to aerate our cool season lawns like tall fescue.

An attractive lawn starts with a healthy root system. Roots make up 90% of the grass plant and require oxygen to thrive. Soil compaction restricts the oxygen supply and inhibits root growth. Aerating, or moving air into the soil, loosens compacted soil and provides the following benefits:

• breaks up or removes thatch

• improves infiltration of water and nutrients

• increases oxygen supply to the roots

• encourages new and deeper root growth

There are many causes of compaction.

Children playing: Upper 1 inch of soil.

Dogs: Upper 1 inch of soil.

Sports activities (volleyball): Upper 2 inches of soil.

Parking cars on lawn: Upper 3 inches of soil.

Heavy construction equipment: Upper 6 inches of soil.

Core aeration can be done any time the grass is actively growing. It is best to aerate once or twice a year on a continual basis. It takes three consecutive years for the yard to receive the full effect. For cool-season grasses (bluegrass, fescue, ryegrass), the best times to aerate are March, April and September. This should be done before fertilizing, seeding or applying crabgrass preventers. Warm-season grasses (bermudagrass, buffalograss, zoysiagrass) should be aerated from late May through July. It is important to allow at least four weeks of good growing weather. This will give plants a chance to fill the open holes.

Aerator holes should be 3 inches deep, 3 inches or less apart, and about 3/4 inch in diameter. Several passes may be required for correct spacing. Aeration frequency depends on soil type, thatch, and traffic, among other factors.

Turfgrass must have a constant supply of fresh air moving to the surface of every growing root to replace carbon dioxide. Carbon dioxide builds continuously and must be released from the soil. Air exchange, or aeration, takes place in the spaces between the solid particles of soil.

Compaction, excess thatch, and clay soils cause weak-rooted lawns.

As soil is compacted, the natural aeration process becomes ineffective. Air spaces are squeezed out and filled with water. Soil becomes waterlogged and unable to drain. Waterlogged soil promotes shallow root growth. Compacted soil results in turf with low energy, poor growth, and thin, yellow-green characteristics. It does not hold up well to traffic or weather stress. Playing on it would tear the turf more quickly than under normal conditions. Heat stress also causes the yard to wilt sooner. Under any of these conditions, recovery takes longer than it would for a healthy yard.


— Scott Eckert is a Kansas State Research and Extension agent for Harvey County. Horticulture is his specialty. The Harvey County Extension Office can be contacted at 284-6930.