Above: Core aerators have hollow tines that push down and remove a core of soil.
Cooler, fall temperatures have certainly become common over the last couple weeks. But, there are still those nice days when the sun is out, it is fairly warm and you can still take care of some fall gardening tasks. One of those tasks that we try to do each year at McCrory Gardens is to core aerate our turf in the high traffic areas. Granted, we get a lot more foot traffic here than any of you will get in your home lawn, but you probably have some spots where the grass doesn’t grow very well or you might have some bare areas that just get really hard because that is the way you or your kids typically walk or play in the yard. Compacted soils make it difficult for grass roots to grow and penetrate the soil. Water infiltration is also reduced which adds more stress to the grass. You may also notice that you have more weeds in these areas, particularly a very common annual weed, known as prostrate knotweed. Back on the farm in Wisconsin, where I grew up, we had fairly large areas of knotweed where tractors and wagons were occasionally parked. While we would have rather had nice grass growing there, we didn’t try to control it because at least it was green. If we had killed the knotweed, it would probably have been just bare dirt.
You can do a simple test to see if your soil is compacted, besides looking for those areas that do not have good grass growth. You can do it by just taking an ordinary screwdriver and try pushing into your soil in various areas around your yard. If you find an area where it is particularly difficult to push the screwdriver into the soil, compared to other areas, you have probably found an area that needs aeration. It is best to try this test a few days after a rain or after irrigation. If the soil is quite dry, it will also be harder to push the screw driver into the soil.
Some lawns can also have another problem, too much thatch. This is most likely to occur if the lawn is frequently fertilized, watered frequently, and mowed fairly low, less than 2.5”. Thatch is primarily comprised of root and stem tissue that is more difficult for soil microbes to break down. If the lawn is fertilized too much, the grass plants will produced more stem tissues than can be broken down. Too frequent irrigation reduces the amount of air in the upper soil zone, which also inhibits soil microbes from doing their work. Later, when a thicker thatch layer develops, water infiltration is reduced, short mowing heights reduce root growth and the roots end up being in the thatch layer which can lead to more stress and reduced heat and drought tolerance.
Above: Check on your thatch layer by digging out a core or slice of your turf and soil.
If you dig out a core of turf and soil, you should be able to see the soil with roots in it, then the thatch layer which will usually be tan to brown and have a spongy appearance and feel if you squeeze it between your fingers. You should also be able to feel the sponginess of the turf when you walk on it. Some thatch, usually less than ½” is good and nothing to worry about. But if the thatch layer continues to build up to an inch or more, thatch management should be on your to-do list. Core aeration can help with excess thatch too. As the cores are pulled out of the turf, it opens a channel for water to be absorbed into the soil and root zone and it also allows for more air in the root zone which is healthier for the grass and the thatch “eating” microbes.
There are a number of devices and tools that say they help aerate your lawn. Some of these methods include fork-like tools that you push into the soil to spike aerators that you strap on to your shoes and are to then just walk around your yard. But, core aeration is more than just poking holes in the ground. It actually removes a core of soil and turf, usually about ¾” wide and 2-3” deep. The cores are left on the soil surface where they usually break down in a week or two, depending on the weather conditions. This acts to mix soil with the thatch and dead grass clippings near the surface of the turf and also open up channels into the deeper parts of the grass-soil profile. Tools that just push a metal rod or tine into the soil do not really mix soil with thatch and can actually cause localized greater compaction as the surface of the tine pushes soil away from it as it goes into the soil.
Core aerator devices can be purchased at local garden centers or hardware stores. There are some that you can just hook behind your lawn tractor and pull it around the yard. These can work well but usually do not produce very many cores so you have to make many passes around the yard. They will also not work well if the soil is very compacted or if it is too dry. Many rental businesses will also have walk-behind, powered aerators. These usually work much more effectively and are faster than just pulling around other types of aerators. These usually have a drum with the core tubes attached or there are some that have coring tubes that are moved up and down into the soil. But, using them can be hard work. You can also contact local lawn or landscape care companies that will come out and do the core aeration for you.
Above: Powered core aerators are usually available at rental businesses.
Fall is a good time to do core aeration in your lawn because most of our cool season grasses are still actively growing in the cool fall weather and will quickly recover from the core aeration treatment. Remember too that fall is the best time to fertilize your lawn, and you can do it all in the same weekend if the weather is good.