Soil: If you can't drive a garden stake into your lawn when the soil is dry, you have a problem with soil compaction. Compacted soil restricts root growth and prevents water and oxygen from reaching the lawn's roots. Solve your lawn's compaction problem by having your lawn aerated. An aerator removes plugs of soil from your turf, allowing roots to spread out and water to seep into the ground. Clay soils benefit from aeration twice a year, once in the fall and once in the spring, while sandy soils should only be aerated once a year.

Test your soil's pH; soil-testing kits are readily available at most hardware stores and garden centers. Grass grows best in slightly acidic soil, ranging on the pH scale from 6.5 to 7.0. If your soil falls outside of this range, you'll need to add amendments to your soil to bring it back into a healthy range. Two common and affordable amendments are lime and compost; lime increases a soil's pH levels, while compost lowers it.

Water: Surprisingly, lawns don't need much water to maintain their good health; an inch of water per week is usually all it takes to keep grass green. Apply any more water to your lawn, and you risk damaging it. Watering too frequently encourages grass to develop shallow roots, which stunts growth. Wet grass is also at higher risk of developing diseases. To protect your lawn, let it dry out between waterings. Watering early in the morning is best, since water evaporates faster in the afternoon. The best sprinklers for the job prevent evaporation by releasing water close to the ground―try trickle irrigation systems or soaker hoses.

Mow: The more sunlight grass absorbs, the thicker it grows. Since longer grass absorbs more sunlight, you'll need to mow your grass high. Ideally, grass blades should be around 2.5 to 3.5 inches tall. Every spring, sharpen your mower's blades, as dull blades can damage grass. And consider investing in a mulching mower. It shreds grass clippings, which can then be left on the lawn to break down and return nitrogen to the soil.

Thatch: A layer of compacted dead plant material that sits on top of soil, thatch stops water and nutrients from seeping into the soil, starving grass of what it needs to grow. For a healthy lawn, you'll need to reduce the thatch buildup. Raking your lawn can help break up the thick thatch layer. Microorganisms can also aid in the breakdown process; add them to your lawn by spreading a thin layer of topsoil or compost across the grass.

Fertilizer: Grass needs more nutrients―specifically, nitrogen, phosphorous, and potassium―than soil alone can provide. Where soil fails, fertilizer succeeds; fertilizer can give your lawn all the nutrients it needs to grow green and healthy. But over-fertilizing causes thatch to build up, damaging your grass. Your lawn only needs to be fertilized twice a year―once in the spring, and once in the fall. A slow-release fertilizer works best.