Daniel Gill, Merrill, Thomas A. | 5/30/2006 11:23:37 PM
By Dan Gill
LSU AgCenter Horticulturist
Dry weather has been common around the state since last summer, and most of us have received less than the typical amount of rain this year.
Who knows how much rain will fall this summer? But one thing is fairly certain – we will need to water our landscapes during periods of hot, dry weather.
How often we need to water our landscapes varies depending on such factors as temperature, rainfall, humidity, season, plant material and light intensity. Plants need to be irrigated more frequently when the temperature is high, the plants are growing in full sun and there is a lot of root competition for the water in the soil (when a tree is nearby, for instance, or in a thickly planted bed).
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, and the water does not penetrate deeply into the soil. Since 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.
In essence, when you water lightly every day your plants become dependent on you to water them constantly. Watering every day also increases the chances of foliar diseases and root or crown rots.
As relaxing as hand watering is to the gardener, it is not an effective way for most gardeners to irrigate plants growing in the ground. When we water by hand, we tend to apply water rapidly for a short period and then move on. To irrigate properly, water needs to be applied slowly over a sufficient period of time to allow the water to soak deep into the soil.
Enough water should be applied to penetrate into the soil about 6 inches to 8 inches to irrigate thoroughly. 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 than once week.
Early morning is the preferred time to irrigate. This provides plants adequate moisture going into the hottest time of the day when they need it most, and sunlight helps the foliage dry rapidly – reducing the possibility of foliar disease problems. Despite what you may have heard, wetting the foliage of 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 also reduces the amount of irrigation water lost to evaporation.
You can use a variety of methods to irrigate your landscape. These include soaker hoses, common hoses and sprinklers or even underground irrigation systems. You may even use different methods in different areas.
Soaker hoses are made of a material that oozes water slowly. They are ideal for irrigating flower beds, vegetable gardens and shrub plantings. These hoses apply water very efficiently, do not wet foliage – reducing potential disease problems – and can be left in place or moved easily.
Just remember, though, that soaker hoses must be laid fairly close to the plants to be effective, so snake them throughout a bed around the plants. When using soaker hoses, it may be helpful to pin the soaker hose in place with U-shaped pieces of wire to make the hose stay where you want it. Also, you can cover the soaker hoses over with mulch, so they are not noticeable.
The most common and popular method of landscape irrigation is sprinklers, which are also the only practical way to water lawns and large trees. Installed underground systems and hose-end sprinklers are the two basic types.
Underground systems are effective and convenient but expensive to purchase and generally must be installed professionally. Professional landscape irrigation system installers must be licensed by the Louisiana Department of Agriculture and Forestry. Ask to see a copy of the installer’s license to make sure the company or individual that installs your system is reputable and knows what they are doing.
Most home gardeners use hose-end sprinklers. They are less expensive and do not require professional installation. But they are inconvenient to use since they must be moved around to cover large areas and generally must be picked up after use.
No matter which method you’re using, you need to apply the appropriate amount of water.
To figure out how long to leave your sprinkler on to apply 1 inch of water, place several empty cans in the spray pattern of the sprinkler. Then turn on the sprinkler and check the time. When about an inch of water has accumulated in most of the cans, check the time again. The intervening time frame is how long it takes your sprinkler to apply an inch of water, so that’s 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. Did the water penetrate 6 inches to 8 inches? Check several places. This procedure works to calibrate an installed irrigation system or hose-end sprinklers. It also can be used to determine how long to run your soaker hose if you dig and check within a few inches of the hose.
In some situations, such as on slopes and in 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. In these case, you may need to run the sprinkler in cycles – 10 minutes to 15 minutes and then off for 15 to 20 minutes – until an inch of water is applied.
Finally, don’t forget to keep your landscape beds and vegetable gardens well mulched. A layer of mulch covering the soil surface cuts down on evaporation, conserves soil moisture and reduces the frequency of watering.
Get It Growing is a weekly feature on home lawn and garden topics prepared by experts in the LSU AgCenter. For more information on such topics, contact your parish LSU AgCenter Extension office or visit our Web site at www.lsuagcenter.com. A wide range of publications and a variety of other resources are available.