A common question I'm asked, especially at this time of the year, is about lawns with areas that turn a bluish-gray color. These are hard or compacted areas in the lawn.
Compacted soils are one of the main reasons for a lawn's decline. Most people think that insects, diseases, nematodes, improper watering and lack of fertilizers are the cause of most lawns going into decline. If a lawn has a deep, healthy root system, then the lawn can withstand and overcome most of these problems.
Compaction becomes a problem when the top 4 inches of soil are compressed, reducing the pore spaces between the soil particles. This reduction in pore spaces reduces the amount of water, air and nutrients to the grass roots. When soils become compacted, they need to be loosened up. The best way to do this is by aerification.
Aerification is the physical act of removing cores of soil and leaving holes or cavities. Aerification benefits a lawn in a number of ways:
- It loosens compacted soils, and this increases the availability of water and nutrients to the turfgrass.
- It increases the amount of oxygen in the soil. This stimulates root growth, and enhances the activity of organisms that decompose thatch.
- It will thicken the turf. The grass becomes thicker when the tines of the aerator sever the roots, stolons and rhizomes of the grass. When this part of grass is cut, a new shoot will develop. These new shoots will fill in the aerification holes.
- Water run-off is reduced by letting more water infiltrate the soil.
- Drought tolerance is increased. When water has the ability to infiltrate soil to a depth of at least 6 inches, the roots will grow deeper.
In this area, warm-season turfgrasses, such as Bermuda, zoysia, centipede and St. Augustine, are the best grasses for this area. Aerification needs to be done when the grasses are actively growing. Actively growing grasses will recover faster and hide the holes caused by the machine.
The best time of the year is mid-April to late summer. It takes about four weeks for the grass to recover. Lawns that have an irrigation system can be aerified in the hot days of summer. Initially, the grass can dry out faster with all the open holes, but this lasts a short time. Irrigating for a longer period of time after aerification will allow water to go deeper in the soil. If no irrigation is present, it is recommended to aerify in late spring to early summer because generally more rainfall occurs then than in mid-summer.
There are numerous types of aerators. Some have solid tines, some are spoon-shaped, and some have hollow tines. The hollow tines do the best job of aeration. Cores of soil should be left on top of the turf. The hollow tines make a neater hole and bring up less soil than the spoon type.
The deeper the tines go, the better. The closer the tines are, the better aeration job.
Solid-tine aerators can cause problems. The tines make a hole in the soil, but at the same time are forcing the soil particles around the hole closer together.
In small areas, a spade fork can be used to loosen the soil. The spade fork should be pushed in the soil as deep as possible. The spade then should be rocked back and forth.
Penetration depth depends on soil type, soil moisture, tine diameter and the weight and power of the aerifier. Clay soils usually need more aeration than sandy soils, but sandy soils can become compacted. Soil moisture is important when aerating. The soil needs to be moderately moist, which makes it easier to penetrate. Do not aerate a wet soil. If the soil sticks to the equipment or your shoes, it should be allowed to dry.
The cores that are left on the surface after aerification can be raked back into the turf to act as a top-dressing. Also, there are organisms in the soil that aid in the decomposition of thatch.
Aeration works best when done in two directions. The second pass needs to be perpendicular to the first.
Reach Charles Phillips, a retired Columbia County Extension Service agent who operates Hort Consulting, at email@example.com.
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