Compaction is a misused term in lawn care. I believe the term is propagated by the lawn care industry so they can charge $250 to aerate your yard.
True compaction almost never happens in a homeowner's yard. True compaction is caused by mechanically driving the air out from between the soil particles while the soil is saturated with water. Typically this happens at the edge of a cattle tank where the animals sink into the soil while getting a drink. Ranchers call it "pugging" the soil. It also happens if a livestock producers allows the animals to linger in a pasture during a multi-day rainstorm event. The soil gets saturated and the animals just moving around on it drive the air out. It can also happen where heavy equipment is driven on saturated soil. Note that this rarely happens during home construction because home construction workers take every minor rain event to take the whole day off. IN the sports industry you will see football fields and golf courses becoming compacted because they allow play during the rain. As the players walk and drive carts over saturated soil it can become compacted.
Then what is the hard soil that occurs in a normal lawn? It is not true compaction. It is simply soil where the beneficial fungi populations have died out. The fungi in the soil send hyphae out into the soil which helps to separate the soil particles. As the hyphae intrude, the soil particles move farther apart allowing air and water to penetrate much easier. These fungi must have adequate moisture and air to survive. If you allow the soil to dry out for more than a few weeks at a time, you can lose your population of beneficial fungi. This is why, even though you have a drought tolerant grass like common bermuda, you should still continue deep watering every week or two during the hottest part of summer. But if you have allowed the soil fungi to die out, all is not lost. They are still there but they are not doing the job of keeping the soil particles separated.
All you have to do to revitalize the soil is to provide the proper environment for the fungi to thrive. Any kind of mulch you can apply in a quantity of more than 1/2 inch per 1,000 square feet (about 2 cubic yards per 1,000), will cause the environment you want. If you don't want to spend $100 per 1,000 square feet for mulch, you can get a similar effect by spraying the soil with a surfactant. The most popular surfactant for lawns is baby shampoo or any clear shampoo not containing conditioners. Baby shampoo is fairly universally available. Generic is fine. Spray at a rate of 3 ounces per 1,000 square feet (or 90 ml per 100 square meters if you're reading this from Canada or outside the US). Spray the soap and follow that up with one full inch of water (about 2.5 to 3 cm). Then the next week repeat the deep watering, and the following week, repeat the shampoo and water. If that does not soften your soil, you can freely repeat the shampoo treatment. You can test the depth of the soft soil using a screwdriver. Try poking it into the ground to see how hard it is to penetrate and how deep you can get it to go. If you can get to go 8 inches deep fairly easily, you're doing very well. At first you might not get it to go 1/4 inch. Another thing to know is that normal soil will be hard when it is dry and soft when it is moist. When soft it might be a little hard to walk on. But as the soil dries out between watering, by the next week or so it should be hard again. Once you get the soil softened, it should remain soft for years as long as you don't allow it to dry out completely for several weeks.
One of the lawn gurus tried overdosing his lawn by spraying 50 ounces of shampoo per 1,000 square feet, every week, and he saw no problems. Another lawn guru had been using shampoo for awhile attempting to get softer soil deeper and deeper. He had a tree drop a limb and it buried itself 27 inches into the soil. The other lawn forums are using the shampoo method with great success. Of course the huge benefit of shampoo is you can do it easily and save yourself $250 for core aeration.
_________________ David Hall Moderator Dirt Doctor Lawns Forum
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