News Release Distributed 05/31/11

As dry weather persists across much of Louisiana, landscapes are threatened.

“Spring droughts like we are experiencing now are especially harmful to lawns and landscape plants because this is the time of year when growth is most active and plants need nice spring growth to support them for the remainder of the growing season,” said LSU AgCenter horticulturist Allen Owings.

“Water is essential for healthy plant growth, but it can be costly to apply depending on your water source,” Owings said. “Remember, it is important to get water to plant roots efficiently and effectively and keep the moisture in the root zone area.”

How often we need to water varies, depending on such factors as temperature, rainfall, humidity, season, plants and light intensity, said LSU AgCenter horticulturist Dan Gill.

“You need to irrigate more frequently, for instance, when temperatures are high, plants are growing in full sun and a lot of plants compete for the water in the soil – when a tree is nearby, for instance, or in a thickly planted bed,” Gill said. “Proper watering is a function of applying the right amount of water at the appropriate times.”

Many gardeners tend to water lightly every day during dry weather, but the water doesn’t penetrate deeply into the soil, he said. Because roots only grow where there is adequate moisture, this results in a shallow root system.

“Shallow-rooted plants are unable to tap reserves of water deeper in the soil and are prone to drought stress in even brief dry periods,” Gill said. “Eventually, your plants become dependent on you to water them constantly. And watering every day also increases the chances of foliar diseases and root or crown rots.”

People have a tendency to water by using the calendar, Owings added. Once a week or twice a weekly is common, and some even irrigate plants daily.

“We all need to learn how to recognize drought stress in plants,” Owings said. Monitor soil conditions in containers and landscape beds. When one plant in a bed needs irrigation, all plants in the bed may not need irrigating. Many factors determine how fast a particular soil or potting medium will dry out.

To irrigate thoroughly, enough water should be applied to penetrate about 6 inches into the soil, Gill said. Applying about an inch of water to medium-textured soils generally will accomplish this. A thorough watering should not be necessary for established landscape plants more often than once a week.

“Early morning is the preferred time to irrigate,” Gill said. “This provides plants adequate moisture going into the hottest time of the day when they need it most. And sunlight helps the foliage to dry rapidly, reducing the possibility of foliar disease problems. And wetting the plants while the sun is shining on them will not burn the leaves.

If sprinklers are used, watering in the early morning when it is cooler and humidity is high reduces water lost to evaporation.

Gardeners often wonder what kind of sprinklers to use on their lawn or what kind of hose or sprinklers to use in their landscape beds. For lawns, Owings suggests an impact sprinkler. These are commonly seen on athletic fields and golf courses.

“In landscape beds, use short-length soaker hoses or use a micro-irrigation, drip system that has individual emitters for shrubs and roses,” Owings said. “For bedding plant areas, spray stakes that attach to micro-irrigation system are nice, but be sure to direct the irrigation water underneath the foliage or downward toward the mulch or soil.”

Underground systems are effective and very convenient, but they’re expensive to purchase and generally must be installed professionally, Gill said.

“Professional landscape irrigation system installers in Louisiana must be licensed by the Louisiana Department of Agriculture and Forestry,” Gill said. “Ask to see a copy of their license to make sure the company or individual that installs your system is reputable and knows what they are doing.”

To figure out how long to leave your sprinkler on to apply one inch of water, first, place several empty cans in the spray pattern of the sprinkler, Gill said.

“Turn on the sprinkler and check the time,” he said. “When about an inch of water has accumulated in most of the cans, check the time again. That’s how long it takes your sprinkler to apply an inch of water – and about how long you should leave it on to thoroughly irrigate an area.”

The best check of how thoroughly an area has been watered is to go back about 15 minutes after watering and dig into the soil with a trowel. “Find out if the water penetrated 6 to 8 inches into the soil,” Gill said. “Check several places.” This procedure also works to calibrate an installed irrigation system or hose-end sprinklers.

In some situations, such as on slopes and heavy clay soils, the water may need to be added even more slowly to reduce runoff. It takes water longer to penetrate heavy clay soils than light sandy soils. Run the sprinkler on for 10 to 15 minutes and off for 15 to 20 minutes until you’ve applied an inch of water.

“In the long run, organic matter in landscape beds helps to maintain soil moisture,” Owings said. “For best results, mulch all landscape beds twice a year.”

The horticulturists recommend pine straw and pine bark as excellent mulches along with hardwood mulch around many trees. Mulch flowers to a depth of 1-2 inches, shrubs to a depth of 2-3 inches and trees to a depth of 3-4 inches.

Rick Bogren