Drip irrigation has several advantages over hand-watering, sprinklers, and other traditional watering methods. Drip irrigation conserves water by putting water exactly where it is needed and keeps paths and areas between plants dry. Hand-watering and sprinklers often deliver water faster than some soils can absorb. Drip irrigation delivers water slowly and evenly over a large area. Water lost to evaporation is negligible compared to overhead irrigation. Drip irrigation saves time. Opening a valve is much easier than standing at the end of a hose. The system can be controlled by hand or even by an automatic timer. They can also be used to apply fertilizers. A final advantage of drip irrigation is disease control. Many diseases occur when foliage is wet. Drip irrigation systems apply water directly to the soil beneath the plants. The plant's foliage stays dry and eliminates the moisture requirement needed by many disease organisms.
Many people have used drip irrigation in vegetable gardens, but landscape plants can also be watered effectively through drip irrigation. To aid in planning your drip irrigation system, sketch your yard on paper. Include all areas that require watering. Also indicate areas such as retaining walls and drives that will act as barriers to your piping. Take note of sloping areas, shaded areas and drier locations.
Drip systems are commonly divided into watering zones. Zones are groups of plants with similar water requirements. For many homeowners, the zones may simply be a division of those plants requiring frequent and infrequent watering. Homeowners with small landscapes may be able to water with a single zone but add additional or faster emitters to take care of thirsty plants. Large landscapes may need zones for hedges, trees, shade gardens, full sun gardens, etc. Most zones in home systems will use less water than the faucet (hose bibb) is capable of delivering. To determine the hose bibb's flow rate, run the water at full force into a measured bucket and time how long it takes to fill. For example, if a five gallon bucket takes 30 seconds to fill, the flow is 10 gallons per minute (gpm), or 600 gallons per hour (gph). The maximum usable flow is 75 percent of the flow rate. In this example, 450 gph. This is the largest zone that the source can supply at one time. Emitters are typically available in flow rates of 1/2, 1 or 2 gallons per hour.
When deciding where to place emitters, there are several important things to consider. Size of root zone and type of soil are very important. Water moves downwards in soil due to gravity and from particle to particle in all directions due to capillary action. In sandy soil, gravity affects water movement more than capillary action. In clay soils, capillary action will tend to spread the water before penetrating very deep. In vegetable gardens and annual flower beds, space emitters every 12 inches or for widely spaced plants 1 emitter for every plant. Perennial flowers should have an emitter at every plant. Small shrubs 5 feet tall and under should have an emitter placed at either side. Large shrubs should have an emitter placed every 3 or 4 feet around the shrub. Place the emitters about 2 feet from the base of the shrub. Trees should have emitters placed approximately every 4 feet within the dripline of the tree.
The object of drip irrigation is to maintain plant moisture levels at near optimum levels. Once the desired moisture content is reached, no more water should be applied. Soil type, plant root depth, air temperature, humidity, and plant age all play a role in scheduling water application. A number of drip irrigation systems are available for homeowners. Most have specific recommendations for irrigation frequency and duration based on soil type, system flow rate and the number of emitters.
Drip irrigation is a different approach to irrigation for many gardeners; however, it is a very efficient way to water.
This article originally appeared in the August 11, 1995 issue, p. 122.
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