Turf Irrigation: What is the Best Time?

Cities throughout Central Texas are struggling through one of the most devastating droughts in our lifetimes. Agriculture losses are already at $3.6 billion and that does not include the loss in landscape plants and turfgrasses. Cities in this area have two major concerns, number one being the amount of water needed to supply all the people with clean drinking water and number two having enough system capacity to meet the extremely high demand during all these hot days.
Fortunately most cities have enough water, if we conserve, to get us through this hot summer. During cooler times when landscapes don’t need as much water we see both the aquifers and lakes stabilize and who knows maybe we will get some rain soon. The other problem, having enough capacity, is simply of function of when we water our turfgrasses! There is no doubt that most people have learned to water turfgrasses early in the morning so that the grass has time to dry out to prevent diseases. Every city water department can testify to how well we know this by the amount of water used during the 3 AM to 7 AM time period. It seems as if every sprinkler system in the city fires up during this time and the consequent drop in pressure for the city water system frustrates even the best water department managers.
So you may have been notified by your city water department of voluntary changes to your watering schedule. Of course most cities want you to avoid watering in the hottest, windiest times of day, usually 10 AM to 6 PM. But to avoid over taxing the system you may be asked to change your irrigation times to 8 PM at night or 7 AM in the morning or even midnight! Almost everyone who hears of these changes immediately worries that they will cause lawns to get diseases and die or that all the water will evaporate before it hits the ground. Nothing could be further from the truth. In the hot summer time we just don’t have the conditions, night or day, for turfgrass diseases to develop because of irrigation. The grass dries too quickly for disease to develop. And being so hot, even at night, we see very little difference in irrigation evaporation - morning, evening or night. Currently evapotranspiration rates are running around .25 inches of water per day. Looking at the data the real increase in evapotranspiration rates is not the time of day you water but whether there is wind or not. Rates can increase 50% or more with just 10 mph winds!
Next there is some confusion on how much to water? It is really quite simple, all turfgrasses need 1 inch or less of water per week, period! In looking at the area’s soils and knowing the turfgrass water requirements based on evapotranspiration we actually only need ¾ of an inch a week to maintain a beautiful green lawn. The next question is how many minutes do I set my sprinkler system to water ¾ inch. Set out empty tuna cans around your lawn, water until they are nearly 1/2 full and do this twice a week and you will have given your lawn more than enough water to be beautiful!
Now what is the take home message? Just this, follow the city’s water schedule and watch how much water you use and you won’t hurt your landscape but you will help us all get through these tough times.