HOW TO: Install drip irrigation in new plantings
The first year after planting is the most critical time for trees and shrubs. They are adapting to different exposures, temperatures and available water while trying to establish a root system. During this first year, water is the primary reason behind success or failure.
Why? Because the roots are limited to the size of the planting container or root ball. During dry, hot summers, plants depend on the water you provide to the root zone, which is limited to a small portion of soil. If you water the plant properly throughout the first season of growth, it should establish a root system by the second season (or sometimes the third, depending on the plant species and size of the plant) that can take care of the plant with little additional water.
One or two plants are easy to water through the summer by placing a trickling garden hose at the base of the plant for 20 minutes or so every day or two. But for a landscape of 20 or more newly installed trees and shrubs, it's impossible to manually water everything properly.
Using lawn sprinklers is an inefficient approach to watering newly planted trees and shrubs for the following reasons:
Water will likely penetrate only a few inches into the top of the root ball.
Much of the water is intercepted by the foliage over the root ball.
The majority of the water is applied outside the root zone — an inefficient use of water.
Weeds are being watered between the plants.
Frequently wet foliage can encourage disease to develop.
By contrast, drip irrigation is a much more effective means of watering newly planted trees and shrubs because:
Water is applied directly to the root zone.
Water is not wasted on the surrounding area.
Water is applied at a slow rate that is efficiently absorbed by the root ball.
Foliage remains dry.
So when it's time to establish new plants, consider drip. It could mean the difference between success and failure of a new planting. Here is a basic rundown of drip systems and some tips for successful installations.
Water source. Depending on whether you are considering temporary or permanent placement, follow these guides.
Temporary. You can connect the system line to a water spigot. This is an inexpensive approach to water during the first year of establishment. By the second or third year, most plants can grow without supplemental irrigation.
Permanent. For systems that will remain in place, such as in arid climates and container gardening, connect to the water-supply line underground and set up a valve similar to a lawn sprinkler system.
Valve assembly. The valve assembly consists of components that you can purchase individually or as a kit.
Backflow preventer. The system should have a backflow preventer, if one is not already in place. This prevents any contamination of the drinking-water supply through the irrigation line. Even if you are using the water spigot as a water supply, it's a good idea to use a hose-bib vacuum breaker connected to the spigot to prevent any back-siphoning.
Pressure regulator. Drip systems run on low pressure. Because static water pressure from the water supply line may be around 75 to 80 psi, a pressure regulator is needed to drop the pressure to about 30 psi. If the drip system were run at higher pressure, it would eventually cause a major leak.
Filter. Emitters at the base of plants distribute water through extremely small openings that debris, such as sand, could plug. Screen filters of 150 mesh are necessary to remove debris from the water supply before it enters the irrigation line.
Valve. For permanent systems, a valve is necessary to control the water. It can be a simple ball valve that requires manual opening and closing. A diaphragm valve — the same type that controls lawn irrigation — is electronically activated and operated by a controller.
Timer. With drip, you may forget the system is on because you don't see or hear it running. That's why timers are important components of drip systems. If the drip system uses a water spigot as its water source, one option is to use an inexpensive timer that hooks onto the spigot. These use a mechanical dial (similar to an egg timer) to set the amount of time to water. However, timers that rely on water flow to drive the timer can be less reliable.
For drip, you wire the diaphragm valves to the controller just as you would with any other type of system. If the valve is in a remote location that's difficult to run wire to, consider a battery-powered solenoid/timer unit. The batteries may last 9 to 12 months before needing replacement, so they don't create a maintenance headache.
Tubing. The line that will supply water to the emitters is ½-inch polyethylene (PE) thin-walled tubing. This is flexible, black tubing that is sold in 100- or 500-foot rolls. Don't confuse this with “funny pipe,” which is thick-walled tubing used as flex-connectors to lawn sprinklers. It would be very difficult to insert emitters into this type of tubing.
From the supply line, feeder tubes (¼- or ⅛-inch tubing) can direct water to the base of the plants.
Emitters. These are attachments that supply water at a constant rate to plants. Flow rates are measured in gallons per hour (gph). The flow rate of an emitter often is not adjustable, so your choices usually consist of units that supply water at 0.5 gph, 1 gph or 2 gph. Emitters may be color-coded so that the flow rate is easy to identify.
Mini-sprays. Similar to emitters, mini-sprays distribute water in a fan or stream pattern. Unlike some other emitters, they may be adjustable and can apply water from 0 to 30 gph. They also may have caps you can remove to clean out clogs.
Designing a drip system
Now that you've got the components, you can begin designing your system. Remember to keep these factors in mind before you install:
Length. Limit your supply line to about 500 feet. Longer lines will lose pressure due to friction losses. This will reduce the rate of application at the end of the line.
Elevation. Elevation affects water pressure at about 0.433 psi per foot of change. For example, if the supply line rises 10 feet in elevation from the water source to the end of the line, about 4 psi (10 feet × 0.433 psi) will be lost. Be sure to take this into account in your designs.
Flow. Limit your flow to about 250 gph. Exceeding this will result in low flow through the emitter and little water reaching the end of the line.
Size of emitters. Although some areas may need less water than others (such as shaded vs. sunny areas), in general you can size your emitters as shown in the table below. Remember that you cannot use the same size emitters for all plants supplied by the same line. Larger plants simply need more water, and you should accommodate this by using larger emitters.
After you gather your components and plan your design, it's time to begin installing your system. Follow these steps to ensure a successful implementation:
Laying out the supply line. Place a roll of ½-inch PE in full sun for a few hours. This will soften it and make it workable. When PE is stiff, it is difficult to bend without crimping.
Have plenty of landscape stakes (u-shaped pins) on hand. These help hold the PE tubing in place, which otherwise tends to curl around and make installation difficult.
Lay out the pipe between plants. You may be able to run a single line throughout the entire landscape. If necessary, you can shorten the supply line by installing a tee to split it.
Install the emitters. Place emitters directly at the base of the plant. This is important because all the roots of newly planted trees and shrubs are in the root ball. By contrast, if you were designing the system to water established plants, you would place the emitters throughout the root zone of the plants, which runs out to and beyond the dripline of the plant.
Use a punch to open a hole in the supply line. It's simply a plastic tool with a sharp point that will punch a ⅛-inch hole in the PE. Because the PE is pliable, the hole will close slightly and tighten around the emitter after you insert it.
If you can route the pipe directly to the base of the plant, then you can plug an emitter directly into the supply line. Simply punch a hole and push the emitter into the line. Some emitters have an insert barb that is sharp enough to be punched into the line without using a punch.
Often, the supply line must run some distance from the plant bases. This means you'll need to use feeder lines to place emitters or mini-sprays at the base of the plants. Punch a hole in the PE and insert ⅛-inch feeder lines directly in the hole. Don't worry if it is slightly loose — the pipe will close around it and tighten up. Note that a ¼-inch feeder line requires a connection barb. Insert the connection barb into the hole and then attach the feeder line to the barb.
Have plenty of “goof plugs” on hand. If you make a mistake or need to move an emitter, it's not a big deal. Just snap a goof plug into the hole to stop the flow.
Flush the system. Before you run the system, leave the end(s) of the PE tubing open and let water run out for several minutes. Soil and debris will get into the line during installation, and if you do not flush it out, it will clog up an emitter.
Close the supply line. Simply bending over the end and crimping the pipe closes the end of the line. You can use a figure-eight end cap by running the pipe through one opening, bending (crimping) it over, and running it through the other opening. This will keep the crimp in place. Alternately, you can use duct tape to tape the end in place.
Adjust emitters. Run the system and check that the emitters are all flowing and placed where you want them at the base of the plants. If necessary, adjust the flow of mini-sprays. Be sure to re-check the system after running it for an hour or two. Feeder tubes or emitters can blow out if they were not fully snapped into place.
Bury the supply line. It's easy to cover tubing with mulch to hide it from sight. If the line runs across turf, it's possible to use a spade to open up a wedge that will get the line below the surface. However, if you have the resources, use a trencher to get the line several inches below the surface to make it less vulnerable to an accidental break from digging.
Maintenance. Once a month, check the system for leaks and plugged emitters. Also remember to remove and clean the filter.
Installing drip is a fairly simple process, and the materials are inexpensive as well. Considering the cost of new plants and the difficulty of hand-watering, investing in a drip system to get a new landscape established is a sensible and cost-effective choice.
Tony Bertauski is a horticulture instructor at Trident Technical College (Charleston, S.C.).
How much flow? Calculating flow requires only basic arithmetic. Simply add up the flow of all the emitters attached to the supply line. For instance, if you plug 10 2-gph emitters and 5 10-gph mini-sprays into the supply line, then you'll have a total flow of: (10 × 2 gph) + (5 × 10 gph) = 70 gph
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