Did you miss the lawn renovation window last fall? Even though September-November is the optimal time to get cool-season lawns looking good, core aerating and overseeding now will help.
Cool-season lawns in this area are primarily tall fescue, Kentucky bluegrass and perennial ryegrass. Of the three, turf-type tall fescue performs the best in research trials for growth in shade, drought resistance and disease resistance. If you have a warm-season lawn with grasses including Bermudagrass, buffalograss or zoysiagrass, wait until they are actively growing in June to make any renovation.
Many of the lawn problems I see are caused by or related to soil compaction. We walk on the lawn, play on the lawn, drive equipment like lawnmowers over the lawn, etc. All of these actions can compact the soil over time. Poor drainage can also cause compaction, and lawns with dense tree roots will benefit from being core aerated. Roots need both air and water.
Bare spots and thin grass cover is not a good solution to the air and water problem. Sometimes this leads to more compaction as soil dries out more rapidly. Bare spots and thin grass can also contribute to erosion. Eroded soil is known as sediment when it enters our waterways and is considered to be one of the biggest pollutants of Kansas lakes and streams.
Core aerating alleviates compaction as well as helping to break up thatch; improving water, air and nutrient infiltration; releasing carbon dioxide from the soil; and encouraging root growth.
Most lawns should be aerated once per year or at least every other year. Lawns with lots of use or with heavy clay soils may need aeration more than once per year.
The best way to core aerate a lawn is to use a machine called a core aerator. You can rent one from local equipment rental shops or hire a lawn care provider to perform the service. A core aerator has hollow tines that pull plugs of soil up and out of the lawn as the machine is driven over it. The plugs are dropped on the surface of the lawn and will break down within a few weeks.
When core aerating, the machine should be driven across the entire lawn twice. Make the second pass at a direction perpendicular to the first.
Another method of core aerating is called spiking. The process involves using solid tines or spikes to put an angular hole in the ground. There are even special shoes available that allow you to aerate the yard simply by walking around on it. Spiking is not as effective as core aeration with hollow tines, but is more beneficial than doing nothing.
Once the lawn is aerated, put some turf-type tall fescue seed down on the bare and thin spots. Use a rake to scratch the seed into the surface enough to get good seed to soil contact. There are many varieties of turf-type tall fescues available — look at the label on the back of the grass seed bag rather than the over-promising descriptions on the front.
If you plan to use crabgrass preventer, apply it prior to April 15 (or about the time the redbuds are in full bloom).
Irrigated lawns may benefit from an application of slow-release fertilizer in May, but otherwise Kansas State University recommends waiting until September to fertilize. Lawns that are fertilized in the spring often exhibit more stress in the summer than lawns that are only fertilized in fall.