Richard L. Parish | 11/19/2004 10:14:00 PM
Drip irrigation is an excellent way to water your trees and shrubs. It will work very well on both fruits and ornamentals.
Drip irrigation allows you to precisely meter water directly into the root zone of the trees and shrubs without wetting foliage or watering the weeds between plants. You have more choices in irrigation rate and component configuration with tree and shrub systems than with garden systems.
With shrub and drip systems, plain tubing (about ½ inch in diameter) is run past each plant, and then discrete emitters are installed in the line beside each plant as needed. The emitters can be installed directly into the tubing, or a smaller tube (called spaghetti tubing) can be run from the line tubing to an emitter several feet away.
You first use a special punch (a drill will work, too) to make a hole in the line tubing, then push in the barb of an emitter or a double-ended barb to connect spaghetti tubing. You can install the emitters anywhere along the line, and you can use more than one emitter per plant. For instance, you might use one emitter for a small azalea or blueberry plant and several emitters for a live oak or peach tree. It is also possible to install a tee in the spaghetti tubing and branch out to two emitters from one hole in the line tubing.
Tree and shrub systems can be equipped with a wide variety of emitter types and sizes. Some emitters just drip out water at low rates (Figure 1). Other drip emitters can be mounted on short stakes and put out a light spray or mist of water. The spray may be 90-, 180- or 360-degree. If spray emitters (mini-sprinklers) are used, they should be mounted low enough to spray under, not on, foliage.
Emitters are available with a wide range of flow rates, typically from ½ gallon per hour to 10 gallons per hour. Obviously, the lower flow rate emitters have smaller orifices and will plug more readily.
You must be careful if using different types of emitters in one system or zone to match the delivery rates. If you mix 1 gph emitters and 5 gph emitters on the same line, some plants will get five times as much water as other plants. You can, however, deliberately use different flow rate emitters to provide different amounts of water to different plants. For instance, you might want to put half as much water on a cactus as on an azalea, or you might want more water on a larger plant.
It is usually better to use multiple emitters for larger shrubs and trees rather than a single high-flow-rate emitter since you want to irrigate a larger area under a tree rather than just putting more water on a small spot. Adjustable emitters are available and work very well (Figures 2, 3). They allow you to fine tune your irrigation rate to individual plants.
You will need a pressure reducer to lower the pressure to about 15 psi and a good filter to prevent plugging of emitters. You will also need a backflow prevention device. You may want to lay out branch lines if your plants are not all along one line. You can use a timer to shut off the water automatically after a predetermined time, or you can purchase a controller that will fully automate the operation.
One useful component is the "goof plug," a blank barb that can be used to plug any holes you might later decide you don’t need or holes put in by mistake. A special hole punch to fit the emitters you are using makes the job of installation much easier and is inexpensive. A simple ball valve installed at the far end of the line will allow you to flush the line occasionally and can reduce the risk of plugging.
Kits are available from home/garden centers and irrigation suppliers. The kit will usually contain drip line, drip emitters, a pressure reducer and a filter. You can then add additional components as needed to expand the system to fit your situation.
As with other drip systems, it is best to water lightly and frequently, rather than allowing the soil to dry out between irrigations. If you have mulch around your shrubs and trees, you can probably get by with watering every other day. If water runs off, you are overwatering. If you use small spray heads rather than drip emitters, it is best to water at night, early in the morning or in the evening to reduce evaporation loss. It is important to check all of your emitters occasionally to be sure they are working correctly and are not plugged. It is too late to correct the situation if you wait until you see a dead plant. Remember that you want to irrigate the root zone, not just the trunk or stem. The root zone extends beyond the reach of the branches.