Daniel Gill, Merrill, Thomas A. | 4/19/2005 10:28:54 PM
By Dan Gill
LSU AgCenter Horticulturist
In our climate, with an average annual rainfall of around 60 inches, irrigating our gardens generally is an occasional rather than a constant need.
It’s important to keep in mind, however, that the intense heat of summer, which is rapidly approaching, makes proper watering critical during the dry periods. This is especially true for newly installed landscapes, vegetable and flower beds and any new plantings in existing landscapes.
Proper watering is a function of applying the right amount of water at the appropriate times. When you irrigate, water thoroughly and deeply. Then learn to evaluate the condition of your soil and plants to know when you need to water again.
If you water thoroughly, as is recommended, but too often, you will keep the soil saturated with water and reduce oxygen availability to the root system. This will impair the function of the roots and may lead to root rot. Thorough watering should not be necessary for established plants more than once or twice a week.
If you tend to water lightly every day, as many gardeners do, the water does not penetrate deeply into the soil. Since roots grow only where there is adequate moisture, the result is a shallow root system. This makes the plants unable to tap reserves of water deeper in the soil and prone to drought stress in even brief periods of drought and high temperatures. The plants become dependent on you to water them constantly.
When the weather is very dry, watering by hand generally is not effective for irrigating plants growing in the ground. When you water holding the hose with a nozzle or your thumb over the end, water is applied too fast over too short a period for it to penetrate deeply into the soil. To irrigate properly, water needs to be applied slowly over a sufficient period to allow the water to soak 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. Sprinklers most frequently are used to water landscapes, so the question is, "How long should I leave my sprinkler on to apply about an inch of water?"
To figure out how long to leave your sprinkler on, place several empty cans in the spray pattern of the sprinkler. Turn on the sprinkler, and check the time. When at least an inch of water has accumulated in most of the cans, check the time again to see how long it’s been. That’s how long it takes your sprinkler to apply an inch of water – and therefore how long you should leave it on to thoroughly irrigate an area.
In some situations, such as on slopes and heavy clay soils, the water may need to be added even more slowly to reduce runoff. Run the sprinkler on for 10-15 minutes, off for 15-20 minutes, back on for 10-15 minutes, then off for 15-20 minutes and so forth until an inch of water is applied.
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 also allows the foliage to dry rapidly, which reduces the possibility of foliar disease problems. Watering plants while the sun is shining on them will not injure them.
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 and are ideal for watering beds. They apply water very efficiently, do not wet foliage, thus 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. Then cover them over with mulch, so they are not noticeable.
Many types of hose-end nozzles are available. These are good for hand watering plants in containers, newly seeded beds, rinsing off foliage and so forth. Although hand watering is excellent for plants in containers, remember it is not the best way to irrigate plants growing in the ground.
The most common and popular method of irrigation is sprinklers, which also are the only practical way to water lawns. Installed underground systems and hose-end sprinklers are the two basic types.
Underground sprinkler systems are effective and very convenient, but they are expensive to purchase and generally must be installed professionally. Make sure the company or individual that installs your system is reputable and that their workers know what they are doing. Often these systems are put on an automatic timer for convenience, but they frequently are set to come on too often and for too short a time.
Most home gardeners use hose-end sprinklers. They are less expensive and do not require professional instillation but are inconvenient to use, since they must be moved around to cover large areas and generally must be picked up after use. There are many types of sprinklers that cover areas of various sizes and shapes. Watch spray patterns and include sufficient overlap to ensure even watering of an area. It also is important to leave the sprinkler going long enough to water the area thoroughly.
Finally, don’t forget to keep your landscape beds and vegetable gardens well mulched to conserve soil moisture and reduce 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.