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Taking the mystery out of drip irrigation.

For any size of garden and all kinds of plants except lawn, drip irrigation is the most efficient way to get water down to plant roots. Even though the collection of components can look intimidating at first, drip is easy to install, even for the beginner. The key is good planning and design. Laying out the lines requires only cutting and hole-punching. The system shown here, designed by The Urban Farmer Store of San Francisco, took about a day to put together, including installing the valves and an automatic controller. Because it's a small garden, planted with just a few trees and with shrubs that have similar water requirements, it required only three valves to water the entire area one for the small front yard, one for a shady courtyard, and one for the back garden shown here. An additional valve runs lawn sprinklers.

Although a larger garden would need more valves, the principles of design and installation are the same.

Design the system on paper first

To design a drip system for your own garden, it's best to plan it out on paper first so you can figure out how to lay out the lines and what parts you need (use grid paper so you can draw the plan to scale and take measurements off it). The more detailed your plan, the easier it is to select the right parts.

First draw in the areas designated for planting, then mark down types and locations of plants. Learn the water needs of your plants. Are they drought tolerant or do they need frequent irrigation? If you're planting a new garden, group the plants according to water needs.

Ideally, you should separate plants with different water requirements and root depths, and use different valves to deliver just the amount of water that each grouping of plants needs. Mark down on paper which areas will be covered by each valve. Also, mark your sun and shade zones, so you can water these separately too. Remember that every garden has its own idiosyncrasies-soil textures, wind patterns, and the like-that will affect the water needs of the plants.

A large rear garden that has a number of trees, groups of containers, a vegetable garden, a perennial border, and separate planting beds of drought tolerant shrubs and lush shade plants would need six valves. Plants in the front garden would be on their own set of valves.

In small gardens like this one, where it isn't practical to put trees and shrubs on different valves, you can compensate by using 2-gph (gallon-per-hour) emitters for trees, 1-gph emitters on large shrubs, and 1/2gph emitters on small shrubs. Try to keep shallow rooted annuals and ground covers on a separate valve, since they require water more frequently.

Once you've determined how many valves you need, draw in the lines from each valve to the individual plants watered by it. This will help you determine how much tubing to buy. Installation: start with the valves You can regulate how often and how long each valve waters plants by setting up a drip system on an automatic controller. Buy one with enough stations to handle all valves and enough programs for flexibility when scheduling watering times. For more information on controllers, see page 228 of the June 1989 Sunset.)

For a small garden with only one valve, it's easier to run the drip directly off a hose bibb and just turn it on and off as desired, or add a battery-operated timer between the hose bibb and drip filter.) If you use an automatic controller, you also need automatic valves. Install a combination valve and antisiphon backflow preventer (either brass or plastic, depending on your building code) at the water source; shut off water line first. Then run the low-voltage cable to the controller as shown in the diagram on page 95.

If you already have manual valves, you may be able to add adapters to make them automatic. But for most drip systems, it's better to buy the new kinds of valves designed for low flow.

Add a main shutoff valve and a union between the water source and valves so you can turn the system off in an emergency and unscrew the valves for repairs. Assemble the filter and pressure regulator as shown at the top of page 95. Make sure the arrows on all units point in the direction of water flow. Wrap threaded connections with nonstick plumbing tape.

Using a thread-to-tubing adapter, attach 1/2-inch polyethylene tubing to the valve assembly and run the distribution line out to the garden. To make a 90' turn below valve, cut tubing an inch or so above ground and insert a compression elbow.

Laying out the lines

For the garden shown here, water is distributed to a shrub border with 1/2-inch tubing that runs from the valve, along a fence, and around the perimeter of the garden. A 1/2-inch line runs along the house to the front yard.

If you run into obstructions like a concrete walk or driveway, use PVC pipe to force a tunnel below ground to the other side. Because that pipe will be clogged with soil, replace it with a new piece of PVC that's cut several inches longer than the width of the obstruction. Using PVC cement, glue a PVC elbow into each end- add compression fittings to adapt the elbows for drip tubing.

From the main line, run lateral lines to each plant. Most of the ones shown here are 1/8-inch tubing, but 1/2-inch tubing is more common and best for large systems. You can make cuts anywhere along the distribution line to intall the laterals; attach them with compression Ts (shown at top on page 96) or elbows.

Snake lateral lines around and between plants so each one gets water; use hairpin metal stakes to hold the tubing in place. Install end caps on the end of every line. For large shrubs, make a U around the plant so tubing runs on opposite sides; for small shrubs, you can run a line down just one side. To accommodate a tree's large root system, you can either make an entire loop around the tree or run one line down each side of the trunk.

For newly planted trees, install a J-Ioop off the lateral line, cutting the tubing at least I 1/2 times longer than is needed to circle the small root system; install an end cap. Wrap the loop around the trunk. As the roots expand, open up the loop and add more emitters (and more tubing, if necessary.).

If you're running a drip system to a patio, conceal tubing under decks, along the edges of pavement, or in other places where it won't be seen. You can also paint tubing to camouflage it. Use 1/4-inch tubing to water pots and in areas where larger tubing is more difficult to conceal. Flush the line, then install emitters To remove any dirt or grit that might have gotten into the system during installation, flush the lines as shown in the photograph at left. If you add emitters before flushing, they may clog. Install emitters with a hole punch (shown at right on page 96). As a rule of thumb, use 2-gpb emitters for plants in sandy soil, 1-gph in loam soil, and 1/2-gph in clay soil. Space emitters evenly over the root system. Use two or three for larger shrubs and one right next to the plant for small shrubs. Established trees need 3 to 10 emitters, depending on tree size.

Arrange the tubing so the emitters sit a third to half of the distance from the trunk to the outer branches. For new trees and large shrubs, place emitters right on the rootball and then move them out as the roots grow into the surrounding soil. To supply a continuous band of water to rows of plants, you can either make a chain of in-line emitters as shown on page 96 or buy preinstalled in-line emitters. The 1/4-inch tubing is easier to hide under foliage, but the preinstalled kind is better for running long distances.

You can also use minisprays and misters for watering closely spaced ground covers and flowers, or plants that like high humidity and wet foliage, such as ferns.

Attach them to 1/4-inch tubing and set them on stakes (see photograph above right); rearrange as plants grow and block sprays. Or insert them directly into the lateral line as shown above center. After you've finished installing the emitters, turn on the system to make sure all the emitters and sprays are working correctly. The first time you run the system for its normal cycle, check moisture spread and depth of penetration in the soil to confirm that you have enough emitters in the right places and are running the system long enough.

Wait several hours after the cycle finishes and then dig down in several areas around root zones. If necessary, add more emitters or run the system longer. Afterward, you can bury the lines by covering them with a 2- to 4-inch layer of mulch. 1-1
COPYRIGHT 1991 Sunset Publishing Corp.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Date:Jul 1, 1991
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