Drip irrigation is the most practical, efficient way to water plants. In a typical system, water travels through lengths of polyethylene tubing; emitters attached to the tubing deliver water where you want it—near plant roots— in a gradual flow adjusted for the plant’s water requirements. Drip systems eliminate water runoff and reduce water lost through evaporation and overspray by up to 70 percent.
Drip is especially useful in special planting situations. You can install in line emitters for plants growing between paving, create a multicycle mist sys tem for frequent watering of shallow- rooted plants, make a ring of in-line emitters to water large containers, and run tubing along eaves to supply hanging pots. Used in conjunction with an automatic controller, or timer, such a system offers both flexibility and excellent control.
A complete drip irrigation system usually includes a range of components (see Ill. 14), designed to deliver water to all the plants in your garden. Most components are sturdy and hassle-free. Installing such a sys tem is relatively easy, even if the area you’re covering is extensive; for planning help, see earlier section.
Following is a rundown of typical components and how they operate.
Water-delivery components
Though they all deliver water to plants, emitters, misters, mini-sprays, and mini-sprinklers (see Ill. 15) play particular roles in a garden watering scheme. Knowing the differences will help you design the system that’s best for your garden. For help in choosing the right emitters for your soil type and the plants you’re watering, see the chart.
Ill. 14. Typical drip system components: Controller; Male adapters;
Elbow; Antisiphon control valve; Male adapters; ¼-inch microtubing;
Emitters. Drip emitters deliver water from the main distribution tubing to plants. They’re best for watering individual plants, since water placement is more precise than with sprays. Usually, emitters can be completely hid den from view.
Most emitters have barbed ends that snap into ½ or 3/8-inch polyethylene tubing, or push into the ends of 1 microtubing. Some are barbed on both ends, so you can create a chain of tubing and in-line emitters. Others come preinstalled in tubing.
Emitters are color-coded for flow rate; red, green, brown, blue, pink, or black may signify rates of ¼-, ½-, 1-, or 2-gph (not all manufacturers use the same colors to identify the same rates).
Multi-outlet emitters have up to 12 outlets per head.
+ Diaphragm-type emitters have an interior diaphragm that opens or closes to control flow as pressure changes. They’re generally self-flushing and automatically compensate for varying water pressure.
+ Diaphragm emitters are best for hilly terrain, slopes, and systems using long lines of emitters. Don’t use them if your pressure at the water source is lower than 5 psi (pounds per square inch).
Turbulent-flow emitters have twisting pathways that reduce pressure by creating turbulence; this also makes them partially pressure-compensating. The wide channels pass debris, so this type is less likely to clog, making these emitters especially useful where water quality is poor.
+ Vortex-type emitters spin water in interior chambers to lower the pres sure where the water exits. Water that’s high in calcium tends to clog this type of emitter.
Misters, mini-sprays, and mini-sprinklers. Inserted into tubing or run off microtubing and mounted on stakes, these spread water over wider areas than do emitters but still operate at low flow rates and low pressure. They’re particularly useful for closely spaced ground covers, flowers, and vegetables. As plants grow taller, they may block the spray, but you can rearrange sprayers or add new ones so plants get sufficient water.
All three types come in a range of flow rates. Higher water pressure in creases the flow and gives wider coverage.
+ Misters deliver a very fine spray. They’re commonly used for ferns and other plants that need high humidity and frequent watering.
+ Mini-sprays come in various spray patterns, including rectangular for strips and 90°, 180°, 300°, and 360° circular patterns that are good for irregular shapes as well as for open spaces.
+ Mini-sprinklers, or spinners, emit large droplets that are less affected by wind than droplets from misters or mini-sprays. Their wide, full-circle patterns—from 10 to 30 feet—are useful for large areas.
Tubing
The standard way to distribute water in a drip system is through ½ or 3/8-inch polyethylene tubing attached with plastic fittings and laid on the surface of the soil, where the tubing can be obscured by a mulch.
Flexible and easy to cut, the tubing is connected without glue. Both inside and outside diameters can vary widely, so it’s a good idea to keep a sample of the tubing you use on hand in case you need to add to the system later on.
Use ¼-inch micro-tubing (often called spaghetti tubing) to connect mini-sprays and mini-sprinklers to the distribution lines. Because it’s easier to conceal than larger tubing, microtubing is also good for distributing water to containers and hanging baskets on decks and patios. Don’t choose it for general use—it’s fragile and too easily knocked away by rakes or animals.
99 Ill. 15. Detail of drip components: In-line pressure regulator; Porous pipe; Microtubing; Preinstalled in-line emitters; Perforated pipe
Continuous-flow pipe
When you need to water a row of plants, continuous-flow pipe, which emits a continuous band of water, is a quick and easy solution because it eliminates the need for emitters. All types should be used with a pressure regulator and filter; the porous kind works best at 5 to 10 psi.
- Preinstalled in-line emitters give a continuous band of water. This drip- line tubing is sturdy, clog-resistant, and generally trouble-free. It comes in 100-foot rolls.
- Perforated pipe is good for flower and vegetable beds, but not for permanent installation, because the holes have a tendency to clog.
- Porous pipe (ooze tubing) is best for underground installations, as in a vegetable bed, where the tubing stays moist. If the pipe dries out between watering cycles, calcium may build up inside and clog the pores. It’s available in 100-foot rolls.
Supply controls
Controllers, valves, filters, and more specialized components automate your system, making it more versatile and efficient.
Controllers. The heart of the system, a controller, or timer, is an electronic device that automatically regulates the operation of each system connected to it. For all but the smallest system, choose a multiprogram automatic controller that allows you to set up watering frequency and duration. If you use two or more separate control valves, you can water on different schedules automatically.
Controllers that can be scheduled in hours, rather than just minutes, are the most versatile, since they run long enough to deep-water trees and shrubs. A less-expensive option is a controller that can repeat its cycle several times during the day.
Valves. All systems need a control valve combined with an antisiphon device. For help in choosing the suit able one for your system, call your water department. Valves designed for low-flow shutoff (½ gpm or lower) are good for small systems.
One helpful device is an automatic rain shutoff valve. Mounted out in the open, on a fence or near your house, it measures rainfall and automatically shuts off your system when water reaches a certain (often adjustable) level. When the water evaporates, the sys tem turns back on.
The simplest such devices rely on natural evaporation; mount them in direct sun. More sophisticated types have a heating mechanism that speeds evaporation, useful where humidity is high or brief summer storms are a common occurrence.
Filters. Most household water is clean, but sediment can get into the line during flushing of city water pipes or from old galvanized pipes in your house. That’s why your drip system needs a good-quality 150 to 200-mesh flushable Y filter, one that uses fiberglass or stain less steel screens to filter out sediment that might clog the emitters. In stall the filter just below the control valve.
Pressure regulators. Most low-volume systems are designed to run best at water pressures between 20 and 30 psi. However, household lines generally range from 50 to 100 psi, with some areas as high as 300 psi. To compensate, you need to install a pres sure regulator (usually one for each main line) between the filter and the line. This device reduces the pressure to a rate that won’t blow the system.
Fertilizer injectors. Spreading fertilizer over the soil is not an effective way to feed plants that are watered by drip irrigation. A fertilizer injector installed between the control valve and the pressure regulator puts fertilizer directly into the plants’ water supply. Some injectors work by dissolving tab lets, others by injecting liquid or soluble dry nutrients into the flowing water. Some injectors are integral with filters.
Which emitters are right for your system?
Plants |
Soil type |
Emitters |
Low shrubs |
Sandy soil Loam Clay soil |
One 2-gph emitter next to plant One 1-gph emitter next to plant One ½-gph emitter next to plant |
Medium-size to large shrubs |
Sandy soil Loam Clay soil |
Two or three 2-gph emitters placed evenly around plant Two or three 1-gph emitters placed evenly around plant Two or three ½-gph emitters placed evenly around plant |
Small trees (to 8-foot-wide canopy) |
Sandy soil Loam Clay soil |
Three to six 1-gph emitters or two or three 2-gph emitters, installed on a J-loop or on two lines set on opposite sides of trunk Two or three 1-gph emitters, installed as above Two or three ½-gph emitters, installed as above |
Larger trees (10 to 15-foot diameter) |
Sandy soil Loam Clay soil |
Four to ten 2-gph emitters, installed on a J-loop or on two lines set on opposite sides of trunk Four to ten 1-gph or three to six 2-gph emitters, installed as above Four to ten ½-gph or three to six 1-gph emitters, installed as above |
Ground covers spaced at least 2 feet apart |
Sandy soil or loam Clay soil |
One 1 -gph emitter at rootball One ½-gph emitter at rootball |
Closer ground covers with less distinct root zones |
Any soil |
Overlapping mini-sprays or mini-sprinklers (or see below) |
Beds of flowers, ground covers, and vegetables |
Sandy soil Loam Clay soil |
Several 2-gph emitters spaced about a foot apart in a row Several 1-gph emitters spaced about1½ feet apart in a row Several ½-gph emitters spaced about 1½ feet apart in a row |
Container plants |
Potting soil |
One or more ½ or 1 -gph emitters, depending on pot size |
Emitter flow rate |
Amount and pattern of coverage |
|
 |
||
A gallon of water in a drip system moves differently through different kinds of soil. The numbers for each give the maximum horizontal coverage at different emitter flow rates (expressed in gallons per hour). The shading shows the vertical wetting patterns. |
||