What is "ET" and why is it important?
ET, or reference evapotranspiration, is one of the most important things to consider when scheduling run times for your irrigation system. The problem is, most people have never heard of ET or considered it when irrigating their landscapes. Fortunately, it is a fairly simple concept that can save you money and grow healthier plants.
Evapotranspiration is the combination of water that is evaporated and transpired by plants as a part of their metabolic processes. "Reference evapotranspiration" or "ET" is simply the amount of water needed in a year of average weather. As the days get longer and warmer (March to July) ET, or the plant's need for water, gradually increases.
A very common, but incorrect, watering practice is where the irrigation system is turned on to full capacity around March when rain usually ends. The system is then left running for peak summer water needs until well into the fall when it begins raining again. Remember that in the fall, though the afternoons may be warm, the days are much shorter and the growing season is ending for most plants. Therefore, plants need much less water. The efficient irrigation scheduling technique is to readjust the system run times to match the actual plant water needs.
We monitor weather information including temperature, humidity, and wind. Based on actual weather conditions, we evaluate how much water is needed to replace the water that is used by your plants and make this information available to water conscious consumers in our Daily ET Rate chart shown above.
Watering depends upon the turfgrass variety, climate conditions, soil absorption rate and the heat intensity. Watering is not hard, but some understanding helps. If you apply only a little water every few days, you will moisten the soil only ½ to 1 inch deep, and that’s where the roots will be inclined to grow. However, if you water deeply and less often, the roots will grow several inches deep, and they’ll stay moist for a longer period of time thus establishing a lawn that is deeply rooted and more inclined to be drought tolerant. If you water correctly, as a rule you can water less often.
When to water..
Wait until you see first signs of stress in your lawn before you water. If footprints remain in the turf, the blades are too limp to spring back. Also, a grayish cast to the lawn indicates that it is dry and needs water. Ideally, watering should be done as early as possible in the cool of the day (6 am to 10 am). Do water your lawn during the winter months especially if the weather is dry or before a hard freeze.
How long do I water...
This will vary depending on the type of sprinklers used and water pressure. Setting uniform containers throughout your lawn and then running your sprinklers for 30 minutes will allow you to determine your water output. Apply the water only as fast as the soil can absorb it.
How much water does my turf grass need...
Every lawn is different so there is no set rule for watering your lawn or landscape. You may find it necessary to modify the general weekly water requirements to meet your individual needs. The key to remember is that you must keep adequate moisture in the root zone so that the plant remains healthy. Environmental conditions, wind, exposure, and rainfall will all affect your estimates.