When the soil under a lawn becomes compacted from foot traffic or heavy equipment, it loses its springy texture and becomes hard as a rock. Water puddles or runs off, and lack of air to the roots causes the turf to deteriorate in appearance and vigor; the lawn often develops thin or bare patches.

To correct this condition take these steps:

1. Mow the lawn, then make holes in the sod by running a rented aeration machine over it. Or do the job by hand with a tool made for the purpose.
2. Rake up the plugs.
3. Spread 40 pounds of gypsum and 15 cubic feet of organic soil amendment (such as finely ground bark) over each 1,000 square feet of lawn. Apply a complete lawn fertilizer according to package directions. When the soil or thatch is hydrophobic (so dry it sheds water), also spread on a pelletized penetrant according to package directions.
4. Rake these materials into the holes. Follow up by watering deeply.