Soil is a layer of earth made up of organic bits and air pockets. The size of these organic bits is what determines your soil type. Sandy soil is made of larger particles, clay soil is made of very small bits and the silt that combines with the two to form loam is considered a medium build. No matter what kind of soil you have or what you're growing, your lawn needs to be watered until there is no more runoff. This will take roughly two inches of water a week, or enough to penetrate 8 to 10 inches (20 to25 cm) into the soil [source: VanDerzanden]. If you have sandy soil, which drains quickly, you may need to water it more often to ensure that roots have been reached. Automatic sprinklers, which can run often for short periods, are a good option for this soil, as are drip-line systems, which deliver a steady amount of water and eliminate run-off. Adding organic material also helps soil retain moisture.
For clay soil, which holds water well but doesn't drain easily, you may need to space out your watering sessions. Hose watering allows you to control times and visually measure your soil's saturation, and the easy drip-line method makes timely watering a breeze. Be careful, however, not to overwater, as too much water keeps air from reaching the roots, ultimately drowning them. Working with clay soils can be tricky in this regard, so make sure to monitor your soil until you've established the best watering cycle and amount for your yard.
If you have developed your soil into a consistent loam base, you can play around with these watering methods. Consider an automatic sprinkler system or use a hose as needed, keeping in mind that different plants have different irrigation needs.
Read on for plant basics for each soil type.