Try to picture 27,154 gallons of water, enough water to fill a 6 foot deep pool that measures 20 feet by 30 feet. An acre plot of grass needs that much water in a thorough watering. Even a moderate 5,000 square foot lawn will consume 6,000 gallons of water. Now before you start totaling your water bill, there are a few things to consider. You don’t have to supply all of that water with a hose and sprinkler. A good part of that will be supplied through rain. If your soil has enough organic matter in it, it will help store the moisture once it receives it instead of puddling and running off (clay) or leaching through the soil (sand). This number also changes in the summer. Lawns naturally go into a dormancy period when extreme hot weather is present, but we have been instilled with the notion that our lawn must be green ALL season long instead of letting nature run its course. A dormant lawn will resume normal growth when the stress effecting it has subsided (either heat or cold). In many cases, over watering can do more harm than good. Again we place more emphasis on keeping up with the Jounces instead of doing what our lawn wants us to do. The more water a lawn gets early on in the season, the more water it will need later on. Continuous moisture in the Spring will only create lazy roots that will not grow down into the soil, but instead remain up at the surface. On the other hand, too little watering may not be helpful at all. A sprinkler left running 10 minutes in one spot will not have enough time to soak the soil and the water will evaporate, not even getting to the roots. The trick is to water in a way that encourages grass to grow deep roots, generally 6 to 18 inches deep. Now some grasses just won’t grow that deep, such as bentgrass, which has shallow roots. Also keep in mind that root length is in direct relationship with shoot height; if you mow low, the roots remain shallow. It is also important to keep in mind what kind of soil you have. The soil will determine when you should water, and even the type of sprinkler you should use. At full saturation, clay soils hold up to 2 1/2” of moisture per foot of depth, and supply turf for almost 2 1/2 weeks without any rain. Loam can hold 1 1/2” of moisture per foot of depth, and sand can hold 3/4” of moisture. You should not water until the reservoir in the soil is almost dry.
How much do I water?
Remember the statistics from above. If you apply two inches of water, it would not be too much for a clay soil (2 1/2”), but for a sandy soil, which can only hold up to 3/4”, the 2” would be wasted. Infiltration rates (the amount of water that can be absorbed in one hour) has to be kept in mind along with the holding capacity. These two numbers will effect what sprinkler you use and for how long. If you have a clay soil with a sprinkler running at 1 inch per hour, only 0.1 inch will be absorbed and the rest will be run-off. Not a good deal for you or your lawn. Flow rates for sprinklers are normally printed on the side of the box it came in. What if your sprinkler puts out more water per hour than the soil can accept? Let’s say that your sprinkler puts out 0.6 inches per hour and you have a clay soil that will accept only 0.1 inches per hour. You should run the sprinkler 10 minutes on, 50 minutes off, and you won’t waste a drop. Infiltration rate of water varies between each soil type.
Soil Texture - Inches/hour
Sandy loam 0.5
Clay loam 0.15
The key to watering is to make sure the lawn receives 1” of water per week, including rainfall. It is that simple. When watering, do not water after 3 p.m. in the afternoon. Any moisture after this time can sit overnight and become a host for disease. Make sure the lawn dries out thoroughly before nightfall comes.
Remember top water only when necessary, before noon of possible, and when you water, water thoroughly.