Determining how much water your turfgrass needs is no easy task. Species of grass, turfgrass health, soil type and health, time of year, microclimate, weather, etc. all greatly affect how much water you should apply. Typically, a higher mowed turfgrass has a deeper root system, and therefore can draw water from a larger volume of soil. This allows one to apply less water than the turfgrass will use, and may provide sufficient time between waterings for rainfall to replenish the water in the soil.
Again, there is no clear answer to this question. However, the old saying is deep and infrequent. Deep means that enough water should be applied to fully wet the soil profile. This may mean that multiple waterings are necessary to prevent runoff from occurring. Infrequent means that one should refrain from further irrigation until the soil begins to dry or the turfgrass begins to show signs of stress. We want the turfgrass to develop a strong root system, watering frequently can result in a weak and short root system.
The best time of day to water is in the early morning. This often coincides with the lowest wind speeds and reduces the duration of leaf wetness. Watering in the evening or at night may encourage disease development as the leaves remain wet until morning.
An indicator of turfgrass stress is wilting. The turf will look gray-green or even bluish, and is often the first sign of moisture stress. The turfgrass may be able to withstand this stress over a few days, without loss of quality, however, you should be ready to get some water on the turfgrass.
One of the easiest methods to monitor soil moisture is by using tools one probably has in their garage. A pocket knife, screwdriver, or trowel can be used to monitor soil moisture. A moist soil will not provide much resistance when the tool is pushed into the soil. However, as the soil dries, the tool will not push into the soil as easily. With frequent monitoring, one can really hone in one when it is time to irrigate.
Electronic soil probes can be placed in the lawn that will prevent the irrigation system from running until the soil is sufficiently dry. This can greatly reduce the amount of water applied over the season, and likely will increase turfgrass health. Smart irrigation controllers are also becoming more popular as they can utilize on-site weather data or a weather network to help manage irrigation.