How to Build a Drip Irrigation System
Sprinklers, which spray water into the air where it is easily evaporated or lost to the wind, are inherently inefficient. They spread water over large areas, regardless of whether there are roots throughout the area to absorb it. Plus, constantly wetting the leaves contributes to foliar diseases in many crops. In contrast, drip irrigation systems deliver water directly to the soil, precisely where it is needed. Drip systems are geared for precision and are highly adaptable, allowing gardeners to fine-tune how much water each and every plant receives.
Home scale drip systems allow vegetable beds, perennials, trees, shrubs and even potted plants to be irrigated by one system controlled by a common “brain,” a computerized timer that opens and closes a series of irrigation valves according to a programmed schedule. Each valve supplies water to a different irrigation zone, feeding the plants water through a network of plastic tubes and drip “emitters.”
Note: this project requires some plumbing and carpentry skills.
Step 1—Install Timers, Valves and Hardware
You can connect a drip system directly to a hose faucet and turn it on and off manually as needed, but automated valves make life easier. While you focus on other tasks—or go to your day job—the system does the watering for you. The most basic timers are battery powered or solar-powered and are designed to screw onto a hose faucet; in this case, the timer and the valve are a single unit. Multiple valves are needed for larger gardens, however, in which case a separate multi-zone timer is mounted somewhere nearby.
- Connect to the water supply with ¾-inch PVC pipe. Install a shut-off valve in the PVC line so the water supply to drip system can be turned off in the event that repairs are needed. If the water source is a municipal supply, a backflow prevention device may be required by local codes at the junction with the drip system.
- Install a “T-fitting” every 6 inches in the PVC pipe for each valve that will be used. Connect the valves to the PVC pipe.
- Attach 24-volt sprinkler wire to the solenoid on each valve (the cylindrical part at the top that opens and closes the valve electronically) using weatherproof wire nuts.
- Run the sprinkler wire to the timer and connect each wire to the corresponding terminal inside the timer.
- Thread a drip filter onto the outlet of each valve.
- Thread a pressure reducer onto the outlet of each filter (a 30 pounds per square inch pressure reducer works for most drip applications).
- Thread a hose-to-compression adapter onto the outlet of each pressure reducer (this converts the threads of the pressure reducer to the type of fitting used by most drip systems.
Step 2—Install the Tubing and Emitters
The plants that will be irrigated with the drip system should be divided up according to proximity and how frequently they need water. A vegetable garden might need water every day, while an orchard might need it once per week or less often. As a general rule of thumb, each valve can water about 1,000 square feet of vegetation, so plan the system accordingly.
- Push one end of a roll of drip tubing into the compression fitting side of the hose-to-compression adapter of the first valve (1/2-inch or 5/8-inch tubing is typically used). Drip systems use compression fittings, which are connected to the tubing using a wiggling motion while simultaneously pushing the tubing into the fitting.
- Uncoil the roll of tubing throughout the area to be irrigated by that valve, staking the tubing to ground as you go with U-shaped metal stakes.
- Push drip emitters into the tubing where it passes directly by the base of a plant. There are special tools for making a hole in the tubing so the emitter can be popped into place, but the tip of a standard U-shaped irrigation stake is also effective for making a hole.
- Use ¼-inch “spaghetti” tubing to deliver water to plants that are not immediately adjacent to the larger supply line. Barbed connectors are needed to connect the two types of tubing.
- Repeat the process with the other valves/zones.
- Manually open the valves one by one to flush water through the tubing to remove any soil that may have gotten inside during the installation process.
- Use an ‘end cap’ compression fitting to close off the end of each line of tubing. Conceal the tubing with mulch if desired.
Fine-Tuning and Customization
Drip systems are bit like Legos—there are an infinite number of possible configurations. There are elbow, “T” and straight couplings for both the larger supply tubing and the smaller spaghetti tubing, so the network of water supply can be routed exactly where it needs to go. If you make a mistake or change your mind, there are plugs and caps that allow you to reconfigure whenever you want. Emitters come in ½-gph (gallon per hour), 1 gph and 2 gph sizes, so you can customize how much water each plant receives. There is also tubing with emitters built in at 9-inch, 12-inch, 18-inch and 24-inch spacing to make it easy to set up drip systems for rows of vegetables that are planted the same distance apart.
Timers offer several other ways to fine-tune the system. Each zone can be set for a different length of time and a different interval—every day, every other day, every three days, etc. Most timers also have a feature that increases or decreases the duration of each irrigation event based on the season. As the weather cools off in fall, you can crank the system down to 90 percent, 80 percent, 70 percent, etc., and vice-versa in spring. There is always a button that turns the entire system off temporarily in the event of rain. However, the “smartest” drip systems are wired to moisture sensors and satellite-driven weather stations that calibrate the watering program to provide exactly what the plants need without any intervention from the gardener.