Drip irrigation offers an even wider variety of components than does high-pressure irrigation. Here are the elements you need to took at before you begin to plan a drip irrigation system.
Choosing the Whole Ensemble
Each company supplies a full range of drip emitters, sprinklers, misters, porous line, and in-line emitters, not to mention tubing, stakes, and fittings. Often these parts, though they took alike, are not compatible. For example, most irrigation parts are now color-coded to make replacing them easier, yet different manufacturers don’t necessarily use the same color codes. Purchase all components from the same manufacturer.
Head Assembly
The head assembly consists of several pieces of equipment that connect at the point where your drip system taps into the household supply line — usually at a hose bibb. It conditions the water entering the drip system. Some of its components are necessary, others optional.
Pressure Regulator This necessary part of drip systems keeps the pressure from blowing lines apart, and allows the emitters to work as they were intended. Pressure regulators range from a simple insert with a reduced-flow hole in it to an adjustable model with pressure gauge. Pre-set regulators are the most commonly used. There is no reason to change the pressure once you decide on a line of emitters to purchase.
Backflow Prevention Device This device keeps negative pressure from sucking garden water into your household water system. It is required by code in most communities, and should be included even if it isn’t required.
Filter Even if you are using very clean city water, it’s a good idea to filter it. Small particles of rust can find their way into the line and plug up emitters. Filters come in several configurations. The most useful and easiest to clean is the Y filter. The bottom leg of the Y holds a cylinder of wire mesh. It can be removed by unscrewing a cap, making cleaning simple.
Fertilizer Injector This optional piece of equipment makes fertilizing easy. It injects a measured amount of liquid or dissolved fertilizer into the line. Fertilizing drip-irrigated plants presents some problems for conventional fertilizing methods, but this device overcomes them easily and effectively.
Some filters can double as fertilizer “injectors.” A block of solid fertilizer, usually provided by the manufacturer of the filter, is placed inside the filter cylinder. It dissolves at the right rate to feed the plants. For more information, see Fertilizing With Drip Systems.
Tubing
In common parlance, 1/2-inch polyethylene tubing is often called “hose.” Smaller tubing is always called “tubing,” and PVC pipe is called “pipe.” Drip systems use 1/2-inch polyethylene tubing for at least the supply and header lines and sometimes all the lines, with 1/4-inch, or more rarely 1/8-inch vinyl tubing (“spaghetti tubing”) serving for lead-in tubes and lateral lines, especially for container gardens and micro-sprinkler systems. To connect the supply line to the water system, elementary aboveground drip systems often use garden hose, but more permanent situations generally use buried PVC pipe or poly tubing for the main line.
Emitters
There are three categories of emitters: porous pipe, punch-in emitters (including misters and micro-sprinkler heads), and emitter lines.
Porous Pipe This is the easiest and least expensive emitter option. Snake it around plantings, hook it up to a hose, and turn it on. Hide it with a bit of mulch. Generally made of recycled tires, it oozes water from tiny pores. How far the water travels horizontally varies according to your conditions, so do some tests before deciding on the permanent location of the pipe. Of course, it doesn’t have to have a permanent location. Simply pick up porous pipe and move it as needed. On the other extreme, it can be buried 2 to 6 inches deep and become part of a permanent system. Porous pipe can be cut into sections and placed in lateral lines to give coverage similar to that of poly pipe.
On the negative side, due to the numerous pores situated irregularly over the entire surface, inner water pressure control is not possible. As a result, porous pipe waters unevenly, losing pressure toward the end of each length and overwatering low parts of its run while letting higher ones dry out. It can therefore he used efficiently only on flat ground.
It is especially important to use a fine filter (about 200 mesh), because the pores are easily clogged. Also, because the fittings for porous pipe tend to come apart under even moderate pressure, a special pressure regulator must be used to keep the circuit below 10 psi at all times. Porous pipe is most often used in flower beds and vegetable gardens, under hedges, around large trees, and in mass plantings of shrubs — areas where its slightly uneven water delivery will not cause problems.
Punch-In Emitters These water outlets can be inserted directly into pipe after you punch a hole into it. They have an inlet barb at their base so that they won’t pop back out. They can be installed anywhere along 1/2-inch poly pipe; simply make a hole with a hole punch and put one in. Or, they can be inserted in the end sections of 1/4-inch or 1/8-inch tubing. Some emitters have self-piercing inlet barbs to punch their own holes. just push and twist, and they’re in.
Emitters come in regular and pressure-compensating forms. The latter are the better choice. They give off the same amount of water throughout the circuit even when there is a major difference in elevation or the tubing is particularly long.
Punch-in emitters have different flow rates, usually 1/2, 1, 2, and sometimes 4 gallons per hour. In general, use 1/2 gph emitters for clay soils, 1 gph emitters for loam soils, and 2 gph emitters for sandy soils.
If you can see that some emitters in your system are not supplying enough water, simply replace them with those that are one flow rate higher, or add more emitters. If some sectors get too much water, replace the emitters with those of a lower flow rate, or remove one or two emitters and plug the resulting holes.
The three main types of punch-in emitters are drip emitters, misters, and in-line drip emitters.
Drip Emitters The most popular punch-in emitters, these are suitable for containers, vegetable gardens, flower gardens, trees, and shrubs. They make up the foundation of drip irrigation, literally delivering water drop by drop and leaving the surface of the soil almost dry while keeping roots moist. They can be punched into 1/2-inch tubing laid on the ground or inserted into the ends of 1/4-inch or 1/8-inch tubing and held off the ground by stakes. Some manufacturers produce drip emitters incorporated into stakes.
Misters These are most popular in greenhouses and with specialists who grow high-humidity plants such as ferns and bromeliads. Otherwise they are used only in very dry climates to keep fine-leaved annuals, perennials, and tropicals in top shape. In less arid climates, they are sometimes used to humidify hanging baskets.
Most give off a fine mist that humidifies the air but rarely collects on the leaves. Those designed to give larger water droplets serve a double purpose: They moisten the air, and the droplets that form drip down to the base of the plant to water its roots. Because misters must be run at regular intervals during the day, but only for a few minutes at a time, they should be on a different circuit than any other emitter and preferably on a controller.
Misters must be attached to their pot using a clip or stake; each manufacturer has its own device. Some misters can be, or already are, incorporated into a special combination stake that can be inserted into potting soil or nailed or screwed to an outside support.
In-Line Drip Emitters These emitters are a hybrid between a drip emitter and an emitter line. Like punch-in emitters, they are inserted individually into the water line according to need. Like emitter lines, however, they fit right into the line and not on its periphery. Water simply flows through them and continues on, allowing some water to drip out as it passes.
In-line emitters are simple to install. Cut the tubing wherever water is needed, insert the barbed ends into the cut section of the tube, and push back together. Most are designed for 1/4-inch tubing only. They have a more limited range of flow rates than do drip emitters, usually only 1/2 or 1 gph. In-line emitters are used mostly in flower boxes and vegetable gardens because they are most efficient at watering small plants in short rows.
Micro-Sprinkler Heads Also called low-volume sprayers, micro-sprinkler heads take their place between drip irrigation and sprinkler irrigation, right where the differences begin to dissolve. Micro-sprinkler heads use low water pressure and narrow-diameter pipes as drip systems do, yet apply water in a fanlike spray as sprinklers do. They are not as efficient as punch-in and in-line micro-irrigation, since they lose some water to evaporation; yet they waste less water than high-pressure sprinklers.
You can think of micro-sprinkler heads as less powerful relatives of high-pressure heads. They can spray in full circles or increments of a circle, even in strips. Most cover a radius of 6 to 11 feet and are ideal for small beds. They are usually set in beds on tube-like risers and don’t retract into the ground after use. With careful placement, they are relatively inconspicuous because they are so narrow.
These heads are most popular in flower beds, mass plantings, and ground covers. Because they don’t retract and have restricted range, they can’t be used on lawns other than as incidental sprayers in areas of overlap.
Emitter Lines
True emitter lines incorporate equally spaced emitters directly into 1/2-inch pipe. As water runs through the line, some drips out. The emitters come preinstalled at 12-, 18-, 24-, and 36-inch spacings and are rated to dispense 1/2 or 1 gph of water. Lines with 1/2-gph emitters are used for clay soils, lines with 1-gph emitters for loam soils, and lines with 2-gph emitters for sandy soils.
All emitter lines have the turbulent-flow design to keep them from clogging. In most cases, especially on a long line or on a steep slope, use pressure-compensating emitter lines. Sold in rolls, emitter lines can be cut to length and connected to the main line or other laterals in the same way as any other poly pipe.
These practical and durable watering devices might be hard to find but are worth looking for because they give excellent results in flower beds and vegetable gardens, under hedges, around large trees, and in mass plantings of shrubs. They are simply laid on the ground and covered with mulch. They are also much less subject to breakage than punch-in emitters because the emitters are actually part of the pipe and they can’t accidentally be pulled apart.
On the down side, the regularly spaced emitters don’t allow as much flexibility as individual emitters do. Emitter lines are most practical where groupings of similar plants are evenly spaced.