August 3, 2016
New Thoughts on Watering Lawns
With recent scattered rains, watering lawns isn’t high on everyone’s priority list. However, if you missed out on the rain you may be watering your lawn now and almost everybody will probably have to water a few times in the next month or two.
In the past couple of years, there has been a new twist on efficiently and effectively watering your lawn during the hot summer months. The general concept remains the same, but how much we should water at a time has.
It has been Nebraska Extension’s recommendations for years that it is better to water our lawns deeply and infrequently for the best water use efficiency and for plant health. That hasn’t changed... it is much more efficient, and better for the turf, to apply one inch of water in a single application once a week than a quarter inch of water every other day... or an eighth of an inch every day. The water will soak deeper in the soil which encourages deeper rooting AND the evaporation losses will be less so more of the water goes to the plant.
However, what constitutes deep and infrequent irrigation changes during the growing season. Deep and infrequent irrigation is defined as irrigating only after the first signs of drought stress become visible, water thoroughly to wet the soil to the depth of rooting, and then do not water again until symptoms of drought stress reappear. What is “deep and infrequent” in May is far different than what it is in August, so your irrigation controllers for automatic watering systems need to be changed throughout the year. No more “set it and forget it!”
High soil temperatures decrease root growth while increasing root death, the end result is a shallower and less dense root system. August rooting depth may decrease by 50% or more compared to May rooting depth. Therefore, less water is needed to wet the soil to the depth of rooting. Additionally, water use increases with temperature as the plant uses water to cool itself.
The end effect is irrigation frequency increases during the heat of summer, but the amount of water applied during each irrigation cycle is less. Unfortunately, there is no hard and fast numbers recommended for amount and frequency of irrigation.
Turfgrass species, soil type, slope, exposure, compaction, mowing height and frequency, overall plant health, and daily wind, temperature, and precipitation will determine the amount of irrigation required on each individual lawn. It is further complicated by irrigation method. If an underground system is used, the volume, pressure, nozzles, head spacing, and condition of the system will also complicate the irrigation.
A good way to tell how deep in the soil the water has soaked is to take a large screwdriver and poke it in the turf in several places. When the soil is moist, it will slide into the soil easily. But when the soil is dry, you can still poke the screwdriver in, but there will be much more resistance. If it slides in easily to a depth of four to six inches, you do not need to water until the turf starts to show signs of moisture stress.
The bottom line is that turfgrasses require water for optimum performance, but they much prefer slightly drier conditions over slightly wetter conditions and are extremely capable of withstanding slight to excess drought or bluegrass lawns, but not fescue, can tolerate a drought-induced dormancy. Therefore, always error on the dry side when it comes to irrigating your lawn. Not only will the turf perform better, you’ll also reduce your overall water use and save on your water bill.
For more information on watering turf and summer lawn care, go to the UNL turf website at http://turf.unl.edu or contact your local Nebraska Extension office.