Core Cultivation: (Aerating) Lawns
Curtis E. Swift, Ph.D.
Colorado State University Extension
The use of a core cultivator has the following advantages:
- improves water penetration into compacted soils and through thatch and mat layers.
- reduces water runoff. Runoff from turf areas may carry pesticide residues and fertilizers into neighboring storm drains and streams causing pollution problems.
- improves fertilizer movement to the turf roots.
- allows greater levels of oxygen to reach the soil in exchange for carbon dioxide and other gases.
- enhances turfgrass shoot and root development
- increases soil microbe activity at the depth of the aerator's penetration as well as in the thatch layer - resulting in reduced thatch and mat layers
The spike-type aerators that push a large solid spike into the soil increase compaction in heavy clay soils. Aerating is done to loosen the soil, not compact it further. Check with your Extension office for the best aerator to use in your soil or stick to the type that removes a plug of thatch and soil in the aeration process.
Timing of aeration programCore aeration is not recommended during the heat of the summer but in spring and fall. If aerating in the fall, do this when at least 30 days of favorable growing weather is anticipated to ensure turfgrass recovery.
Soaking the lawn a couple days prior to aerating should supply the water needed to allow the aerating tines to penetrate to their full depth. If the soil is too moist when aerated, the cores will be pushed to the bottom of the aeration hole causing compaction; if the soil is too dry, the aerator will not penetrate to the proper depth.
When the lawn is dry, aeration equipment cannot penetrate to the proper depth and when too moist, the aeration plugs, which should be removed from the ground, are pushed to the bottom of the aeration hole causing compaction. The soil moisture content is usually just right two days after watering or following a snow storm, assuming the snow has melted. If you can push a screwdriver with a 6 inch blade into the ground without much difficulty the soil is at the proper moisture content. When the aeration process is complete, the holes should be about two inches apart.
Fill Aeration Holes to increase the effectiveness
To increase the effectiveness of the aeration process, the aeration holes should be filled with a fine organic material. The firm that aerates your lawn may be willing to top dress your lawn with this product so be sure to ask. Filling the holes with compost will hold the holes open much longer than they otherwise would be. Aeration holes in clay soils tend to close quite rapidly. While aerating without top dressing is beneficial, you might as well get the most out of the aeration process. Top dressing and filling the aeration holes is critical with clay soil.
The topdressing can be applied before or after the lawn is aerated. Dragging a length of chain link fence over the lawn will help move the compost into the aeration holes. The amount of top dressing to apply depends on the lawn. I have a portion of lawn that has a high population of night crawlers. Their castings create humps that are an inch or more in height making the lawn quite bumpy. In this case I like to apply about ½ inch of fine compost. This is usually sufficient to fill the aeration holes and help level the lawn. Dragging the lawn also helps level the humps created by the night crawlers. If you want to apply ¼ inch of a fine compostit will take three-quarters of a cubic yard per 1000 square foot area of aerated turf. In my night crawler turf I apply one and one-half cubic yards per 1000 square foot area. Be sure the compost has a salt level below 5 mmhos/cm.
Do Not Power Rake.
I could use a power rake to help level the night crawler humps but find the aeration and top dressing procedure does a lot less damage than the power rake. Power rakes tend to tear into the crowns of the grass and increase disease problems. For that reason alone I do not recommend using a power rake or any dethatching device on a lawn. In most cases power raking, in addition to damaging the crowns of the grass plants, only removes dead grass blades that will decompose during the spring months when temperature is favorable for microbe activity. Put your effort into aeration and skip power raking.
Apply Seed to fill in bare Spots.
In those areas where your lawn is sparse, grass seed can be added to the aeration and top dressing procedure. The grass seed should be scatted prior to aerating to permit some of the seed being moved into the soil during the aeration process.
Select the grass seed to be used based on the type of grass your lawn consists of. If your lawn is mostly tall fescue, use tall fescue seed. If your lawn is Kentucky bluegrass, use bluegrass seed. You can also convert your lawn over to a different type of grass but this will require killing off your current lawn and working seed into the aeration holes. Tall fescue produces allelopathic chemicals that prevent other grasses from invading its turf. Consequently converting a tall fescue lawn to a more drought tolerant Kentucky-Texas Bluegrass hybrid will require killing the tall fescue with glyphosate, Scythe, Burn Out or Horticultural Vinegar (20% acetic acid vs. the 5% vinegar available in the grocery store) prior to reseeding. The latter three products will need to be applied several times as they do not translocate to and kill the roots like glyphosate.
At the beginning of this article I mentioned proper watering and fertilization in addition to aeration were important to the health of your lawn. Watering every day at this time of year will result in very shallow roots. Water-saturated soil suffocates deep roots. Fertilizing properly is also critical. Avoid the tendency to apply the amount of fertilizer recommended on the product label. Apply only half of the recommended amount of fertilizer this spring. This will help avoid problems with succulent growth and related foliar disease problems.