The water news this year sounds like a lot of recent years — last year excluded. The rain and snowfall since last fall have dropped below the normal expected. However, the way that our weather hops around from year to year, it looks to me like it’s anybody’s guess what can be called normal. And if changeability is normal, we’ve had a lot of normal this year.
With that said, we still live in a high mountain desert. That much has not changed. We can plan on chronic water shortages. Exceptionally dry years drive the point home, but we always need to try to conserve water. Gardens need water and we need gardens for a host of reasons, so we must mesh the need for irrigation with efficient water use.
Drip irrigation is an exceptionally good method to apply a minimal amount of water while still giving plants an ample amount to grow on. Drip systems can reduce the amount of water applied by up to 70 percent. This alleviates overwatering problems and runoff and erosion if the systems are designed and used properly. Since these systems are designed to put the water only where it is wanted, at the base of desirable plants, they don’t water weeds between the rows. You can get out into the garden even during watering because the areas between rows remain dry. This cuts down on the work of weeding and other maintenance operations and greatly increases crop yields by not encouraging the competition.
Unlike sprinklers, which lose a lot of water to evaporation in the air, drip systems lose little water to evaporation. Most of the water emitted reaches the plants’ roots. Soaker hoses put water directly on the ground but drip irrigation is more efficient in precisely regulating water output. Drip hoses disperse a low enough quantity of water per hour that water has time to soak in instead of running off or puddling. The chances for overwatering are also lessened. Unlike soaker hoses, drip components allow use of a wider range of water suppliers, and compensate for changes in water pressure and elevation.
If the emitters are spaced far enough apart, there will be an area of dry surface soil between their moist circles. When rain is absent or infrequent, this dry zone means that weeds will not have enough water to germinate.
All drip systems have several basic components. The starting point is a shut-off valve between the main water supply and the drip components. In a simple system this is the standard hose bib or outside faucet. An anti-siphon valve is required by some building codes to prevent irrigation water from siphoning back into drinking water. Without this valve, dirt, fertilizer and other contaminants can be sucked backward into the culinary supply pipes.
Water contaminants are particularly troublesome for drip systems. Sediment plugs openings and makes the watering uneven. Use a 200 mesh or finer filter in the system before the pressure regulator. For calcium problems, use large orifice emitters. The regulator reduces the pressures to low levels to prevent the system from blowing apart since the components are not glued together.
Specialized hoses are used as header hoses or sub-mains for drip systems. It is formed from low density polyethylene and is very flexible and will curve into a tight arc without crimping. Elbows are available but are rarely used. The header hose is inexpensive and durable. Water is delivered to the soil through emitters or through drip tubes. Emitters are varied parts that are punched into the tubing to control the water flow.
Drip tubes have holes or openings built into special tubing. Drip irrigation kits usually do not have the optimal garden design. Parts from one kit will not fit other kits, and spare parts are usually sold in packets. When purchasing a system, buy from a dealer who stocks standardized parts and will help design your system.
Use a manual or an automatic valve for each separate area. Using an automatic timer or controller is a convenient way to regulate the watering time. Timers that run on water pressure and shut off after a certain amount of water passes through are not recommended, because they will not shut off due to the low water pressure and small volume of water used in a drip system. Electric valves control the entire system using an inexpensive timer.
All irrigation systems are designed to replace moisture lost by both evaporation and transpiration. The evapotranspiration rate is based on a formula that takes into account the air temperature, humidity, dew point, wind velocity and solar radiation. Plants need at least the same amount of water as the ET. One inch of water over 100 square feet amounts to 62.5 gallons. Remember to subtract the rainfall from the amount of water the landscape needs. Tubes can be buried, but leaving them on the surface has many advantages. You will know where they are and can avoid cutting them with hoes and cultivators. Rodents, especially gophers, can cause problems because they can chew through buried lines.
Where elevations along the lines changes substantially, pressure compensating emitters are required. Pressure compensating emitters deliver the same amount of water regardless of the change in elevation or the length of the line. Without these, more water will flow out at the bottom of dips or a hill than at the top.
Estimate the future needs of the planting when planning the drip irrigation system. Take into account the length of each line and the number of lines needed to accommodate the emitters that may be added each year as the plantings increase. Different plants have different water requirements. Group plants with similar needs and put in a system that will accommodate those needs.
Three basic plant groups can be adapted to drip irrigation. These include fruit trees, vegetables, and ornamental shrubs, trees and flowers. When designing the system, determine the flow rate, measured in gallons per hour, or GPH, of the emitters or tubing. The greater the GPH, the faster the water comes out and the broader the area that will be soaked. The GPH is best determined by the difference in soil texture. Sandy soils require a high flow emitter, 2 to 4 GPH, to disperse water sideways. In clay soils, use low flow emitters, 1/2 to 2 GPH 18 to 24 inches apart, or higher flow, 2 to 4 GPH, spaced farther apart.
Experimentation is the easiest way to determine the watering pattern. In dry soil, start one emitter dripping at the correct pressure. Check the water spread every hour by digging alongside the emitter or drip hose at increasing distances away from the starting point. Because each drip emitter applies water to a localized spot, it is easy to check the water level in a soil profile. When water is applied slowly it soaks a deep and narrow area. The soaked area forms a carrot-shaped profile. When water is applied more quickly it soaks a beet-shaped profile. The profile shape depends on the consistency of the soil because sandy soil will absorb water in a carrot pattern as it quickly penetrates, while in clay soil absorption will be beet shaped.
Drip irrigation is ideal for vegetable beds. Suggested dimensions for vegetable beds are 3 to 4 feet wide. Each 3- foot bed needs two lengths of inline drip hose.
Drip installation is not difficult as long as the system has been well designed. Most components easily slide together.
All metal pipe threads should be coated with Teflon tape to make a watertight seal. Flush the drip system after assembly to keep the lines clean and free from emitter clogging dirt. After all the emitters are punched into the line, open the closures and flush the lines individually. When using an automatic controller, check to determine if the lines are turning on and off as planned. Set the timer and observe it as it goes through several cycles.
Keep the system working well by flushing the filter every two to four weeks. Remove algae build up on the screen with bleach and a stiff brush.
Each month flush the drip lines for a minute or two. In severe cases of silting or calcium buildup, clean the emitters by pumping a weak acid solution through the system. Unburied lines should be rolled up and stored inside in the fall. Drain the lines and cover or plug the ends to keep insects or other unwanted creatures from getting inside and clogging the lines the next season. Lines under heavy mulch can be left if all lines are drained and there won’t be any traffic on the frozen soil over the drip line.