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WATER, WATER, WATER!
LSU AG GIVES SUMMER PLANTING TIPS
By DAN GILL
LSU AgCenter Horticulturist
Dry weather has been common around the state during May and into June, and most of us have received less than the typical amount of rain the past few weeks. Who knows how much rain will fall this summer? We can be fairly certain, however, that there will be at least some periods of hot, dry weather when we will need to water our landscapes.
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 temperatures are high, the plants are growing in full sun and they have a lot of root competition for the soil water — 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 and frequently — even daily — during dry weather, but then the water does not penetrate deeply into the soil. Because roots only grow where they have 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. Your plants then 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 typically not an effective way to irrigate plants growing in the ground. When we water by hand, we tend to apply water rapidly for a short period and move on. Applied this way, water does not adequately penetrate the soil. 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 about 6 inches into the soil for thorough irrigation. Applying about an inch of water to medium-textured soils will generally accomplish this. For established landscape plants, a thorough watering should not be necessary more than once week during dry conditions. The best way to determine how often you need to water again is to check the soil in landscape beds every few days, and water when the soil becomes dry.
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. (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 reduces irrigation water lost to evaporation.
You can use a variety of methods to irrigate your landscape. You may even use different methods in different areas.
Soaker hoses are made of a material that oozes water slowly. They apply water very efficiently, do not wet foliage — reducing potential disease problems — and can be left in place or moved easily. Soaker hoses must be laid fairly close to the plants to be effective, so snake them throughout a bed around the plants. It may be helpful to pin the soaker hose in place with U-shaped pieces of wire to make it stay where you want it. Finally, cover the soaker hoses with mulch so they are not noticeable. Soaker hoses are ideal for irrigating flower beds, vegetable gardens and shrub plantings.
The most common and popular method of landscape irrigation is using 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 very convenient, but they can be 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 license to make sure the company or individual who installs your system is reputable and knowledgeable.
Most home gardeners use hose-end sprinklers. They are less expensive and do not require professional instillation. But they are inconvenient to use because they must be moved to cover large areas and generally must be picked up after use.
To figure out how long to leave your sprinkler on to apply 1 inch of water, first, 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. That’s how long it takes your sprinkler to apply 1 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. Did the water penetrate 6 to 8 inches? Check several places. This procedure 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 alternately on for 10 to 15 minutes and 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 moistures and reduces the frequency of watering. •
