ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Thursday, February 22, 1996 TAG: 9602220009
SECTION: CURRENT PAGE: NRV2 EDITION: NEW RIVER VALLEY
COLUMN: Hoein' and Growin'
New River Valley's Master Gardener Association
SOURCE: SARA THORNE-THOMSEN
The dead of winter is not too soon to plan a drip irrigation system that will help prevent the loss of favorite plants to summer's heat and drought.
In a drip system, each plant is watered at the root zone so that water isn't wasted on weeds or paths. An overhead sprinkler wets leaves, which often encourages fungus and bacterial diseases. A drip system can save 20 percent to 70 percent of the water that a sprinkler requires.
The slow, steady supply of water provided by a drip system keeps the soil from drying out, preventing the stress that causes poor crop production. Good soil - a mixture of sand, clay, silt and organic matter - is full of large and small pores that hold the air and water necessary for strong, healthy roots. Sprinklers flood the soil: When the pores fill up, the roots cannot breathe so they cannot absorb water from the soil. Too much or too little water can cause plants to wilt and die.
To choose the best drip irrigation system for your landscape or garden, first figure out the area you need to cover. A full-fledged drip system may not be required. A soaker hose may suffice. Unfortunately, soaker hoses begin to silt up after a few years and stop distributing water evenly.
If the ground slopes or if you need to water more than 50 feet, you will need a complete drip system. This system includes not only a feeder line and half-inch polyethylene tubing punctured at intervals by pressure-regulating emitters, but also a faucet-end pressure regulator and filter. Some systems come with self-flushing emitters that resist clogging by silt, algae or organic fertilizers (which, in water soluble form, can be pushed through the system by a fertilizer injector, an accessory available with most systems).
These systems allow you to use lower quality water, such as rain or pond water. A backflow preventor will keep any impurities in the system from flowing back into the community's drinking water. Drip irrigation works so effectively, because the pressure regulator and emitters slow down the water that escapes from the hose. Generally spaced along the line every 12 to 18 inches (depending on the type of soil in the area you want to water), emitters are designed so that even with the hose running full blast they will not pass more than a gallon or two of water per hour. (In contrast, a garden hose can put out as much as 10 gallons a minute.) With the slowing of the water, the tubing maintains a relatively constant pressure over a run of several hundred feet, which means that the plants at the end of the system will not suffer from drought while the ones at the beginning are being drowned (often the case with soaker-hose irrigation). The slow flow also makes it easier to cover a large area with a single faucet, because less water escapes per minute.
After determining the area to be watered, you will need to know the flow rate (gallons per minute or per hour) of your water system to choose a compatible drip system. If your water system supplies water at a rate of 5 to 7 gallons per minute, you don't want a system that requires 8 gallons per minute. To calculate what your outdoor tap actually provides, turn on the faucet full blast and time how long it takes to fill a one-gallon or a five-gallon bucket. If it takes five seconds to fill a one-gallon bucket, the rate of flow is 12 gallons a minute, 720 gallons an hour; if it takes 30 seconds to fill a five-gallon bucket, the rate is 10 gallons a minute, 600 gallons an hour. As a rule, a drip system should use no more than 75 percent of this capacity.
Once it is installed, you have to calculate how many hours per week you need to run the system. The Extension Service recommends one inch of water per week for healthy plants. Manufacturers provide a formula for figuring this out or you can use the averaging method - one hour of watering every other day, all season long. This method works well with a timer.
The process of installing a drip irrigation system is simpler than it sounds, but don't wait until the heat of July to begin the job. Most makers and purveyors offer free design assistance and free consultation by phone during installation, as well as follow-up support and advice on how to expand or change your system. While you are setting the system in place and those plastic tubes are curling in every direction but the right one, keep in mind the pleasure you'll feel when you turn on the tap and watch as, silently, the earth begins to darken and smell damp, or when you come home from a hot day at work and find your garden already watered, because you bought a timer for your system.
The manufacturers say their systems should last at least 10 years, and they offer repair kits for those unfortunate mishaps caused by a slip of a spade or hoe slicing into the tubing. The lines can be covered with mulch, left in place for the winter without suffering damage, and moved aside for spring or fall rototilling. The estimated cost of 600 feet of feeder tubing plus all the necessary accessories needed to irrigate a 50-by-50-foot vegetable garden ranges from $150 to $400.
There are also systems for special needs. Several companies, for example, make pressure-compensating emitters that allow runs of 1,000 feet on moderately steep hillsides. As is typical of specialized equipment, the cost is almost twice that of the simpler emitters. However, if you want to use water wisely, save money (in the long run), and have healthier plants, then drip irrigation is for you. Here are some sources for drip systems for homeowners: Dripworks, (800) 522-3747; Gardener's Supply, (800) 234-6630; and Urban Farm Store, (800) 753-3747.
The following are manufacturers and/or suppliers of drip irrigation systems and can be called for information about local outlets for their products and some technical support: Dig, (800) 322-9146; Netafim Irrigation, (800) 777-6541; Rain Bird, (800) 247-3782; and Raindrip (800) 544-3747.
Sara Thorne-Thomsen is a Master Gardener.
LENGTH: Medium: 100 linesby CNB