Are we watering efficiently?

  Master gardeners are researching irrigation in our area


July 21, 2005


Victoria County Master Gardener


As president of the Victoria County Master Gardener Association, I have emphasized this year the importance of the efficient use of water in practice and study.


Sharing reliable information and sustainable research are our best means to educate on this subject. The master gardeners are undertaking a several-year landscape irrigation monitoring project at Victoria Educational Gardens and the County Extension Office to study efficient landscape watering in the two test sites.


Water applied will be metered so we can determine the required amount of water needed by the plants to survive and maintain a good appearance. The collected data will later be used to develop a watering formula. This data will be shared with our readers and fellow researchers.


Many of you have read frequent articles in the Victoria Advocate about the supply of water to the Guadalupe River and availability of water for Victoria. Various questions arise concerning the water issue. Will Victoria have an unlimited future supply of water? Are other communities grabbing some of the water that normally would go to the Guadalupe River?


There are three major sources of water supply for the Guadalupe River. One is the Canyon Lake Reservoir, which is at the head of the Guadalupe River and collects runoff water from the Hill Country. The other is the Comal River, which collects its water from springs supplied by the Edwards Aquifer. The Comal flows into the San Marcos River, which feeds the Guadalupe River. The other supply is collection of runoff water from the watersheds that feed the Blanco and Guadalupe rivers.


The Advocate published an article dated June 7, 2005, titled, "Communities to Benefit Soon from New Water Source." This article describes an $82 million project by the Guadalupe Blanco River Authority (GBRA) to supply treated water to communities along with their golf courses west of San Antonio. It is projected this system will take 15 million gallons of water per day or 90,000 acre-feet of water per year. Yes, this is water that would have normally flowed to the Guadalupe River.


The Edwards Aquifer, the other major supplier for the Guadalupe River, is also the major water source for San Antonio. All of us are aware San Antonio is looking for additional water sources because of concern about the Edwards Aquifer's ability to supply the needed water.


The Texas Legislature has recently adjusted requirements for San Antonio to increase its pumping from the Edwards Aquifer. This also reduces Victoria's water resources. During a drought period, the Edwards Aquifer provides three-fourths of the water to the Guadalupe River.


An additional drain on Guadalupe River water is the environmental demand caused by San Antonio Bay to maintain the correct balance of fresh versus salt water. Couple this with a drought period when the Edwards Aquifer provides three-fourths of the water to the Guadalupe and you can see that water in Victoria is a precious resource that we can't waste.


Now for the serious questions: "What are you doing to conserve landscape water usage?" What are the chances that during the summer months our water supply will be limited to household use and external watering restricted to a hand-held hose? This event happened several years ago in San Marcos, a city that gets its water from the Edwards Aquifer. San Antonio and other Texas cities also have gone through restricted landscape water usage in recent dry years.


During the summer months, about half of our water supply is used on the landscape. So if the city of Victoria restricts water consumption, it will probably be the landscape water usage. All homeowners need to learn now how to conserve water on their landscape.


It is not a question of "if" but "when" our landscape water supply will be limited. So an adequate water supply to Victoria and an efficient use of landscape water is essential.


The rule for efficient turfgrass watering is simple: Water the target area to dampen the top 6 inches of soil without letting the water run to non-targeted areas. For a sandy soil, this is about 1 inch of water, and for clay this is about 1 1/2 inches of water. Repeat watering only when plants show signs of distress.


A healthy plant is one with a deep strong root system, developed via watering so that the soil is moist 6 inches deep before you quit watering. Repeat this watering only when the plant is beginning to show stress. This includes all plants in the ground whether it is turf or a zinnia.


Efficiency is obtained if this is done without any water running off of your targeted site. For turf, this may require running several 15-minute cycles. Increased cycles prevent the water from going into the street. Thus you may only need to water your turf once per week or less.


Cutting your turf at 3 inches or higher will encourage deeper root growth and the longer top will shade the soil and reduce evaporation.


Shrubs and large trees should be watered to a soil depth of 12-16 inches in a 6-foot-wide band. The center of the band is the drip line for the tree. This deep watering is only required when the tree is showing signs of distress such as curling leaves or dropping leaves.


Some methods for water distribution are more efficient than others. The most inefficient method of distributing water is in the middle of a windy, hot day using an oscillating overhead sprinkler. Much of the water will evaporate before reaching the ground. A drip irrigation system is most efficient, especially if it is covered with a thick layer of mulch.


Underground sprinkler systems should be checked frequently. Unfortunately, sprinkler heads frequently come off or get adjusted by the lawnmower so they are watering the street rather than the turf. If it rains sufficiently, the system cycles should be adjusted to account for the rainwater. Thus, watering efficiency depends on how the system is maintained and knowledge of the electronic controls.


A quick or light watering every day is unhealthy for the plants and encourages shallow roots. When watering with an open-ended hose, the rate of flow should be reduced and the water should penetrate the soil to the 6-inch depth. Don't just spray water wetting the soil and the leaves of plants. This doesn't soak deep enough and causes fungal diseases.


In watering by laying a hose down for a slow soaking, set a kitchen timer as a reminder so you don't water beyond your target area. Use your fingers or a probe to measure how deep you've watered.


Watch The Gardeners' Dirt for future articles on watering.