One definition of cultivation is the act of improving or working the soil to enhance plant growth. This process works well in landscaped beds or vegetable gardens. However, in a turf situation where a lawn is covered in a permanent growth, cultivation takes on a new meaning. All plants will thrive better when the growing conditions are improved through soil cultivation, and turfgrass is no exception. When discussing turfgrass cultivation, there are three practices that are normally suggested: aeration, verticutting, and topdressing.
Turfgrass aeration is probably the most beneficial cultivation practice you can use, especially on hard, compacted soils. Compaction can occur through a variety of reasons. Foot traffic is probably the most common source of soil compaction in turf, whether it is from athletic activities, such as soccer or football games, or just the repeated walking over the same area of turf. Compaction can also occur from vehicular traffic, such as the parking on or the repeated driving of vehicles over the same areas of turf. A commonly seen problem is when large mowing equipment repeatedly follows the same mowing patterns. Soil compaction can also occur on both sandy as well as on clay soil and anything in between.
Soil compaction in a turf area will destroy the structure of the soil making it impervious to water infiltration, which causes runoff and possible erosion problems. Subsequently, the amount of air reaching the root system will be reduced and this can result in a loss of roots. Once a compacted soil becomes wet, the reduced internal drainage causes a decline in the root system due to a lack of air. All of this will stress and thin the turf stand, which will allow weeds more adapted to these condition to thrive. Over time, you will end up with a weedy lawn as opposed to a nice, uniform turfgrass lawn.
The process used to reduce soil compaction on a turf area is called aerification. Aerification involves punching small holes in the soil through the turf. These holes will allow water and air to infiltrate into the root zone, which will allow for a much healthier root system. It will also open up the soil and allow the soil to dry out better after excessive rainfall or irrigation. This process over time should result in a much healthier turfgrass.
There are several ways to aerify a soil covered with turf. A pitchfork driven into the soil then moved forward and backward as well as side to side may be all that is needed on a small compacted area as long as the soil is not too compacted. For larger turf areas, an aerifier can be used. This machine is engine driven and will accomplish the process by either rolling heavy wheels mounted with attached spoon like tines that scoop out a plugs of soil, or by hollow tines that are driven into the soil using a piston type method. As the tines are forced vertically into the soil, small plugs are pulled out. Many equipment rental companies rent soil aerifiers at a modest cost.
Two other aerification methods that are sometimes used in turf are spiking and slicing. Spiking is identical to hollow time core aerification except solid tines are used instead of hollow tines. Since this method does not pull out a plug of soil, clean-up is much easier and activity on the turf may not be impacted as much. However, spiking with solid tines will increase compaction around the area where the tines enters the soil and is usually limited to use on saturated, heavily compacted soils to help with drying.
Slicing involves the use of drum mounted narrow blades that are driven into the soil creating a small slit in the soil. There is little turf disruption with slicing and can be a benefit in creeping turgrasses by cutting stolons, allowing the grass to thicken over time. Although not as effective as hollow tine aerification, slicing a compacted soil several times during the growing season may improve drainage over time. As with spiking, slicing can cause a slight compaction of the soil where the blades enter since a core is not removed.
Warm-season turfgrass can be aerified starting late spring through late summer, while cool-season grasses are best aerified during early fall or early spring. Timing can also coincide with a seeding project as the seed can be worked into the aerification holes allowing for better germination. One time to avoid aerification is after a preemergent herbicide application. Preemergent herbicides form a chemical blanket over the soil that inhibits weed growth. If you aerify your soil after a preemergent herbicide application you will be punching holes in the blanket and allow weeds to come up. Be sure to apply any preemergent herbicides after the soil has been aerified.
There is no set number of times a turf can be aerified. This is a management tool that can be used when needed. Turf that is heavily used, such as a sports field, can easily be aerified several times during the growing season every year. Sites where compaction is not a big problem may get by with an aerification every two to three years.
Verticutting, sometimes referred to as dethatching or mataway, is the process of removing the layer of organic material that accumulates between the growing points of the turf and the soil. This layer of dead and decaying material is referred to as thatch. All turf areas will contain a small amount of thatch, which contributes to the health of the turf. However, when a thatch layer becomes excessively thick, it can impede the growth of turf. Thatch can impede the movement of water, fertilizers and pesticides into the root zone, as well as providing a good growing environment for insects and diseases to grow. Once the thatch becomes one quarter to one half inch thick, dethatching may be needed.
Thatch is caused by excessive management of the turf. Over-fertilizing and over-watering are the main causes of a thatch buildup. This layer is normally broken down naturally by soil microbes that grow in the area of turfgrass roots. Once the rate of organic material production exceeds the capability of the microbes in breaking it down, thatch accumulates.
Verticutters are small machines that resemble lawnmowers and can be used to pull the thatch out of the sod, which then allows a bagging mower to collect the thatch. A verticutter has a series of small blades situated vertically on a roller. The machine will spin the roller causing the blades to spin, and these pull out the thatch. The process can cause some damage to your turf so should be done while there are still several months left in the growing season to allow the turf to recover. The best way to avoid a thatch problem is to follow the recommended management practices for the specific turfgrass in the lawn.
Topdressing a turf area is simply the process of applying a small layer of sand, compost or a sand/compost mix over your lawn. This management tool will help even out small areas that are not level due to poor soil preparation or poorly installed sod with gaps between the sod pieces. By working the topdressing material into the turf, microbes in the material will be introduced into the thatch layer. They will help to reduce excess thatch naturally adding another benefit to your topdressing.
Topdressing should be done during the summer growing season for warm-season turf, as the turf will need to grow up through the topdressing. Cool-season grasses should be topdressed in the spring and fall. Avoid topdressing cool-season grasses during the stress of summer heat. The topdressing material can be applied by hand, using the shovel sling method, or using a topdressing machine. Some fertilizer spreaders can also be set up to apply a topdressing material. Once a thin layer, usually ¼- to ½-inch thick, is applied to the turf, the topdressing should be dragged into the turf using a drag mat. After aerification, the plugs left on the surface should be broken up and dragged into the turf as well, which also acts as topdressing.
The best topdressing material for your site will vary based on your existing soil type and what you are trying to accomplish with your top dressing activity. Sand is sometimes used on clay soils after a good aerification to fill in the holes made by the aerification. This may improve drainage in some situations over time. If you are wanting to add organics to the thatch layer in order to naturally reduce thatch, a well decomposed compost would be appropriate. However, be careful when selecting a topdressing mix. Heavy topdressing over time can create a layered soil causing a reduction in soil permeability reducing water infiltration into the turf root zone. If you are confused with which type of topdressing material to use, contact a qualified lawn care professional, or your local county Extension office, or the Clemson Home and Garden Information Center.