How to Install a Drip Irrigation System

Whether or not you're new to gardening, you probably already know about the benefits of a drip irrigation system, but you might not be up to speed on the details of installing one. It can look a little complicated, especially when you're browsing through catalogs of drip components, but installation is actually fairly straightforward, and compared to installing a sprinkler system, it's a veritable snap. Because drip tubing and emitters are designed to remain above ground, very little digging is involved, so you can forget about having to disrupt your landscaping with a system of trenches.

Installation usually proceeds in two stages. In the first stage, you establish a mainline that is connected to the water source, which can be a standard 3/4-inch outdoor hose bib or an antisiphon valve normally used to supply a sprinkler system. If you already have a sprinkler system and one of the zone valves is unused, it makes a great water source for a drip irrigation system. You aren't at any disadvantage, however, if the spigot on the side of your house is all that's available because drip components are tailor-made for such a situation.

In the second stage of installation, you connect branch lines and emitters to the mainline to supply water to the plants. If there's anything complicated about installing a drip system, it's probably choosing emitters that supply enough water without overwatering and delivering the water in such a way that roots are nourished. To do this, you have to know the water pressure and flow rate of the water source to avoid overloading the system. Installing a drip irrigation system is extremely DIY-friendly, and once it's in, it requires little maintenance, but emitters do clog, so you can't ignore upkeep altogether.

After you've chosen the water source for your drip system, whether it's an outdoor faucet or an antisiphon sprinkler valve, you need to check the water pressure and flow rate. Drip systems usually operate at lower pressures than normal house pressure, but they need a minimum of 20 to 25 psi. To measure your water pressure, screw a pressure gauge onto the spigot or sprinkler valve, turn the water on all the way and note the reading. If the pressure is less than 25 psi — which could be because of corroded pipes or the building's plumbing configuration — choose another water source.

The flow rate from the water source is an important parameter that determines how many emitters can be operating at one time. To measure flow rate, turn the water on all the way and time how many seconds it takes to fill a 1-gallon bucket. Divide by 60 to get the flow rate in gallons per second. Emitter flow rates are measured in gallons per hour (gph), so to convert your reading to gph, multiply by 3,600. The total output of all the emitters operating at the same time — in gph — cannot exceed this number, or the system won't work.

A drip system often incorporates more than one zone even if the total output of all the emitters doesn't exceed the flow rate of the source, and the reason is because different plants have different watering needs. You can provide a single water source with multiple outlets by using a garden hose splitter or a multiport timer, and once you've done that, you can figure out which components you need for each zone. Installing a splitter also allows you to hook up a garden hose to the same faucet that supplies the drip system, so you won't have to disconnect one to use the other.

When measuring the length of tubing you need for the mainline, keep in mind that the closer emitters are to the mainline, the better they work. Instead of passing a single length of mainline tubing through your garden, you'll want to snake it back and forth to limit the lengths of the 1/4-inch branch lines that feed the emitters. You also want to build in as much flexibility as possible because plants' water needs change as they grow and mature, so the more mainline drip tubing you use, the better. Whenever you need to change the position of a branch line or a single emitter, you can always plug the hole with an inexpensive goof plug.

You lose 1 pound of pressure for every 2.3-foot rise in elevation from the water source to the emitter, and you gain 1 pound for each equivalent drop. That means plants at higher elevations can be underwatered, and those at lower elevations can be overwatered, but problems can usually be averted by using pressure-compensating emitters. Most conventional emitters are pressure-compensating, but not all, so it's important to check.

Drip emitters commonly come in three different flow rates of 1/2, 1 and 2 gph, and they are color-coded so you know the flow rate at a glance. The emitter you use for a particular plant depends on the plant's watering needs as well as the soil condition. You generally need a higher flow rate for sandy soil since it doesn't hold water very well. On the other hand, it's not a good idea to mix flow rates in a single zone, so if one plant needs more water than the one next to it, add another emitter rather than using one with a higher flow rate. You can also help loose, sandy soil retain moisture by spreading mulch.

Some plants and trees need more water than one or two drip emitters can deliver, and for these, you can use bubblers, which have flow rates as high as 13 gph. Microsprayers are also an option for watering ground cover and low-growing shrubs and vegetables.

Installing a drip irrigation system is not a particularly challenging endeavor given how easy it is to fit drip components together, but it does take time, and if you're in a hurry to get your vegetable garden watered, you might consider using soaker hoses with 3/4-inch hose thread fittings that screw directly onto a standard hose bib. You can even connect them to timers, and because they deliver a greater water flow, the timer needs to be on for a fraction of the time that it does with a drip system.

Along the same lines, if you have already deployed a main poly drip line, you can connect 1/4-inch soaker hose with a barbed connector, which is a better option for container gardening than 3/4-inch soaker hose. Even better, consider deploying drip tape with precisely spaced apertures instead of standard poly tubing to water rows of vegetables or flowers.

One last option you might consider is 1/4-inch laser tubing with built-in emitters that delivers water at a preset rate (for example, 0.9 gph). Connect one end to a main drip line with a barbed connector, cap the other end with a goof plug and you have a ready-made series of precisely spaced drip emitters that you can snake throughout your garden bed. When using any of these options, it's important to monitor total flow rate to make sure you don't overextend your water supply.