September is an ideal time to core aerate or power rake Kentucky bluegrass and tall fescue lawns. Along with fall fertilization, core aeration is an important lawn care practice.
Core aeration removes soil plugs to help relieve soil compaction and promote root growth, as well as improve infiltration of water, oxygen and fertilizer into soil. While aeration should be done about once every three years, it could be done annually.
Power raking is for thatch control. It can be damaging to lawns and is only recommended when true thatch is thicker than one-half inch. Thatch is a reddish-brown, spongy mat found between the soil and green grass. Thatch is made up of dead roots and rhizomes. Grass clippings do not contribute to thatch.
This is why we recommend leaving clippings on the lawn. They do not contribute to thatch but they can slowly help increase organic matter content of soil which is beneficial. Research also shows if grass clippings are left, the number of lawn fertilizations can be cut back by one.
While core aeration is the better practice, another argument for it is power raking brings up huge amounts of plant material. Not only must this plant debris be dealt with, but removing it reduces soil organic matter over time.
With aeration, the soil plugs are simply left on the lawn to break down and return soil and organic matter. As a rule, it only takes a week or two for the plugs to break down. This can be sped up by raking them to break up the clods.
And keep in mind if a lawn is power raked too often so there is very little or no thatch, turfgrass can be stressed. A one-half inch or less layer of thatch insulates the growing point or crown from extremes in temperature and from traffic.
If lawns are aerated on a regular basis, thatch is unlikely to become an issue and power raking is unlikely to be needed; so core aeration needs to be done most often and September is the optimum time.
When aerating, the soil should feel just moist and crumble easily when rolled in your fingers. Make enough passes with the aerator that holes are spaced two to three inches apart. Ideally, the cores removed will be 2.5-3 inches long.
If a lawn has not been core aerated in some time, or the soil is dry, it may be difficult to remove this long of a core. If severely compacted, consider annual aeration until a 2.5-3 inch core is readily removed when the soil is just moist.
By doing this, a better rooting environment will be created and this is what leads to dense lawns better able to withstand environmental and pest problems and best compete with weeds.
And by the way, late September into October is the best time to control perennial broadleaf weeds like dandelions, ground ivy and clover with herbicides. Spot treat weeds with a liquid herbicide labeled for these weeds, and be sure to mix the rate according to label direction.
For additional information on improving turf in fall, see the UNL publication “Improving Turf in Fall” found at https://turf.unl.edu/NebGuides/ImprovingTurfinFallPrograms2010A.pdf .
Kelly Feehan is a Community Environment specialist for Nebraska Extension.