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Drip Also called low-volume or micro-irrigation--drip irrigation lets you get water slowly and directly to the roots when plants need it most.

Since we first reported drip in detail seven years ago, we've learned a lot more about how to use it and which products work best. Today, it involves both simple and sophisticated components that you can mix and match to handle any situation. You can combine low-volume emitters, mini-sprays, mini-sprinklers, and misters to form a hard-working, water-thrifty system for all your garden needs.

We also understand better now just how much water plants need. Whether they're thirsty or drought tolerant, shallow- or deep-rooted, drip lets you give them the ideal amount of water.

The industry itself has changed. Many products have been improved; others have fallen by the wayside. Improvements in polymers and resins and the addition of ultraviolet light inhibitors have made polyethylene tubing (commonly called "poly" or "PE") more durable. New emitter and mini-sprinkler designs are almost clogproof. Valves designed for low-volume irrigation are more dependable. And digital time clocks allow great flexibility and better control of watering.

These innovations let you provide the right amount of moisture regardless of how dry or wet the weather and how steep or irregular the lot. Using drip, you can eliminate runoff and reduce the amount of water lost through evaporation and overspray--for a savings of up to 70 percent.

These days, most drip-irrigation components are sturdy and hassle-free. But before you can design a system, you need to know how the components operate. The big picture on pages 72 and 73 shows a schematic combination from hose bibb out, using two methods of distributing water. Here's how the parts fit together.

Start with the emitters ...

and misters and sprayers

You can choose from a variety of emitters that deliver water through small orifices at slow rates--down to 1 or even fewer gallons per hour (gph). Add to these a choice of misters and sprinklers and the option of perforated or porous pipe, and you have great latitude in design.

Three types of emitters

Emitters deliver water from main distribution lines to the plants. Ask at an irrigation supply store to see the choices; someone there should be able to help you select ones that will work well for your terrain and water quality.

Drip emitters are best for watering individual plants. Water placement is more precise than with sprays, and the emitters can be completely hidden from view.

Most emitters have barbed ends that snap into 1/2- and 3/8-inch poly tubing, or push into 1/4-inch microtubing. Some are barbed on both ends, so you can create a chain of in-line emitters on 1/4-inch tubing. Others, like the ones pictured on page 69, come already inserted in poly tubing.

Most of these are color-coded for flow rate; red, green, brown, blue, pink, or black may signify rates of 1/4, 1/2, 1, and 2 gph. Unfortunately, not all manufacturers use the same colors to identify the same rates.

Some emitters are pressure-compensating: they provide a steady flow rate whether tap pressure is 10 or 50 psi. Choose this type if you're working with elevation changes of over 10 feet or running lateral lines over 200 feet, or if emitters on a line add up to over 100 gph.

Multioutlet emitters have up to six outlets per head. Screwed onto PVC risers, they use microtubing to distribute water. Beware: long lines of microtubing can be a maintenance headache.

Diaphragm-type emitters (30 to 45 cents) have an interior diaphragm that opens or closes to control flow as pressure changes. They're generally pressure-compensating and self-flushing (the diaphragm opens at the beginning and end of a cycle to flush out particles). Diaphragm emitters are best for hilly terrain, slopes, and systems using long lines of emitters. The kind pictured on page 71 can be cleaned with a paper clip. Don't use diaphragm types if your pressure at the water source is below 5 psi (systems with too many emitters may also have pressure this low).

Turbulent-flow emitters (30 to 40 cents) have twisting pathways that reduce pressure by creating turbulence--which also makes them partially pressure-compensating. The wide channels pass debris, so this type is less likely to clog--especially useful if water quality is poor.

Vortex-type emitters (about 30 cents) spin water in interior chambers to lower pressure where the water exits. Water high in calcium tends to clog them.

For help in choosing and spacing emitters, see page 74.

Misters, mini-sprays, mini-sprinklers

These spread water over a wider area, but still operate at low flow rates and low pressure. Insert into poly tubing, or run off microtubing; anchor with stakes.

Use for closely spaced ground covers, flowers, and vegetables. As plants grow taller, they may block the spray; some new designs can be extended to spray above the plants. Note: since mini-spray heads stick up, they can be knocked askew more easily than drip emitters.

Which spray head is best? It depends on the area to be covered and on the wind factor. All three types come in different flow rates, and higher water pressure increases the flow and gives wider coverage. Cost is about 25 cents to $1.50.

Misters deliver a very fine spray at a low output (2 to 5 gph). They're commonly used with ferns and other plants that require high humidity and frequent light waterings. Use in protected areas or early in the morning, when it's calm.

Mini-sprays come in various spray patterns (30[deg.]-30[deg.] or 40[deg.]-40[deg.] for strips; also 90[deg.], 180[deg.], 300[deg.], 360[deg]), so they can be used in tight or irregular spaces. Water output varies from 3 to 30 gph; distance (radius) ranges from 4 to 10 feet.

Mini-sprinklers or spinners emit larger droplets that are less affected by wind. Outputs range from 4 to 45 gph. Their wide full-circle pattern--from 10 to 30 feet--is useful for large areas.

Perforated or porous pipe

Consider these when you need to water a continuous row of plants. The tubing is either perforated at regular intervals (the closer the holes, the more the output) or oozes water through pores along its entire length ("ooze tubing"). Both kinds are greatly affected by water pressure; the porous kind works best at 5 to 10 psi.

Perforated pipe (sometimes called soaker hose) is often laser-drilled. Choose it for flower and vegetable beds, but not for permanent installation, since the holes tend to clog eventually (good filters are critical). Cost: about 20 cents per foot.

Porous pipe is best for underground installations, as in a flower bed, where the tubing stays constantly moist. If the pipe dries out between cycles, calcium may build up inside and clog the pores. Cost: $30 to $45 per 100-foot roll.

Five basic components

and one option

Here we list the five required elements of a drip system, and a popular extra. The photograph on pages 72 and 73 shows how they attach to a garden faucet.

Controller. Heart of the system is the basic control unit, often called a timer. For all but the smallest systems, multiprogram automatic controllers are the most versatile and efficient way to water. If you use two or more separate valves, you can water on different schedules: for instance, frequent watering for flower and vegetable gardens, an occasional soaking for deep-rooted trees. A multiprogram clock allows watering on different days.

Clocks that can be scheduled in hours, rather than just minutes, are the most flexible, since they run long enough to deep-water trees and shrubs. A less expensive option is a clock that can repeat its cycle several times during the day.

Depending on the number of programs, stations, and complexity, multiprogram clocks cost $50 to more than $1,000.

Valves. All systems need an on-off valve combined with an antisiphon backflow preventer. For help in choosing a suitable kind, call your water department.

Older types, designed for high-gallonage sprinkler systems, won't shut off completely unless the flow rate is more than 60 to 120 gph--a rate that may not be achieved on a small system.

But design innovations have made new valves much more reliable for low-flow systems. These "low-flow shutoff" valves (make sure they're rated as such) operate down to 1/2 gpm (30 gph), some even to a minuscule 1/10 gpm (6 gph). For most uses, we like the 1/2-gpm valves: they're less likely to clog. Cost runs from $20 to $60.

Almost as important is an automatic rain shutoff valve. Mounted out in the open, on a fence or near your house, it measures rainfall and automatically shuts off your system when water reaches a certain (often adjustable) level. When the water evaporates, the system turns back on.

The simplest such devices (about $32) rely on natural evaporation; mount them in direct sun. The rain shutoff pictured above left (about $60) has a heating mechanism that speeds evaporation--useful if you live where the humidity is high or brief summer storms are common.

Filters. Most household water is usually clean, but sediments can get into the line during flushing of city water pipes, or from old galvanized pipes in your home. That's why your drip system needs a good-quality 150- to 200-mesh flushable Y-filter--one that uses fiberglass or stainless steel screens to filter out sediment that might clog the emitters. "A good filter is the difference between a system that works and one that doesn't," says Joe Hung, agricultural engineer at Cal Poly Pomona. A standard-size Y-filter costs $13 to $25; brass ones, for high-pressure systems, cost about $25.

Tip: For a clue about your water quality, check for grit or rust flakes in the water-holding tank of your toilet.

Pressure regulators. Most low-volume systems are designed to run best between 20 and 30 psi. But household lines generally range from 50 to 100 psi, and up to 300 psi in some areas of the West.

So you need a pressure regulator, usually one for each main line. Preset for 20 or 30 psi, it reduces the pressure to a rate that won't blow the system. Plastic ones cost $6 to $10; brass (for high-pressure lines) are about $50.

Tubing. The standard way to distribute water is through 1/2- or 3/8-inch poly tubing. Flexible and easy to cut, it can be connected without glue or clamps.

For a sturdier but less flexible system, use PVC pipe for main lines and poly for lateral lines (see system at lower far left). Or use PVC pipe just for main lines under walks and patios.

Both inside and outside diameters of poly tubing can vary widely (see top picture). Keep a sample of your tubing in case you need to repair or expand the system later.

Tip: The quality also varies. One way to check: fold a piece in half. If you see white marks at the crimped area or it looks brittle, it's not high quality.

You'll be using 1/4-inch microtubing (spaghetti) to connect mini-sprays and mini-sprinklers to the distribution lines. Hold them in place with sturdy hairpin stakes. There are two choices: poly and vinyl. Vinyl is much more flexible and resists cracking. It's also more expensive, but it lasts longer in exposed areas.

In the past, microtubing was used extensively with emitters to supply water to individual plants in the ground. But that makes the system much more fragile, since microtubing is easily knocked away by rakes, romping animals, and children. Microtubing is still favored to distribute water to containers and hanging baskets on decks and patios, since it's easier to conceal than larger tubing (see upper left picture on page 76).

Fertilizer injector. Spreading fertilizer over the soil is not an effective way to feed plants that are watered by a drip system. That's why many gardeners add one or more automatic injectors--costing $15 to $60 apiece--to their lines.

Some injectors dissolve tablets; others inject liquid or soluble dry nutrients into the flowing water. For details, see "Fertilize plants while you drip-irrigate," on page 174 of the June Sunset.

Planning your system:

do it on paper first

"There's a tendency to view a drip system like a set of Tinkertoys, since you cut, punch, and snap it toegher," says Bob Galbreath of Drip Irrigation Specialists, Los Angeles. "But if you want it to last, you must take a serious approach to its design."

A completely automatic package would likely include most items pictured at left. For a small patio, you may want to use manual valves and a battery-operated timer instead.

To make your shopping trip as productive as possible, plan your system out on paper first. As Tom Bressan of The Urban Farmer Store in San Francisco says, "That prevents frustration, and saves you money and return trips."

Start by marking locations and species of plants; note their water requirements and whether they're deep- or shallow-rooted.

Pencil in water sources and obstacles such as walkways and patios. Mark slopes and elevation changes, since they can affect water distribution. The more detailed your plan, the easier it is to select the right parts.

Check the flow rate from your garden faucet, especially if you're designing a large (over about 600-gph) system or if your house has galvanized pipes that may be partially clogged. To do this, turn off all water indoors. At the faucet, measure how much water fills a bucket in 30 seconds; multiply that figure by 120 to get gallons per hour. (If you get 5 gallons in 30 seconds, the flow is 600 gph.)

To figure out how many emitters you need, see page 74. Their total output in gph should add up to no more than 75 percent of your available water flow at the faucet. If it's more, break the system up so it's controlled by two or more valves.

Find out your water pressure. Call your water department, or buy or borrow a gauge to measure it at the faucet. If it's over 75 to 80 psi, your system is considered high pressure; you'll need to install a brass pressure regulator and possibly a brass Y-strainer (filter) before the valve.

Where to buy your equipment

The best places are irrigation supply stores that specialize in low-volume equipment (look in the yellow pages under Sprinklers). Salespeople can advise you on types and brands of equipment and give you tips on how to put it together. If you need more help, they can usually refer you to an irrigation designer.

It's wise to buy all the materials from the same supplier; you'll get fittings, tubing, and emission devices that work together. But there's no need to buy all one brand--many companies' products can be intermixed.

But note: the parts of most boxed kits aren't interchangeable with those from other manufacturers. With kits, once you buy one brand, you must stick with it. Also, kits may not come with adequate filters and regulators, and the contents may not suit your garden well. Additional or replacement parts are often expensive.

For a list of suppliers, some of which sell by mail, write to Drip Irrigation List, Sunset Magazine, 80 Willow Rd., Menlo Park, Calif. 94025.

Laying out the lines:

Advice from the experts

Group plants on separate valves according to water needs and root depths. If possible, place trees, shrubs, flowers, vegetables, and containers on different lines, so that you can schedule watering to suit their needs. (If you're putting out new plants, don't place a thirsty azalea right next to an unthirsty ceanothus.)

In small gardens, it may not be practical to use more than one or two valves. To compensate for different water needs, use 2-gph emitters on trees, 1-gph emitters on large shrubs, and 1/2-gph emitters on small shrubs--all fed from the same valve. If you can, use another valve for vegetable and flower beds.

For most gardens, use 1/2-inch poly tubing for lateral lines to shrubs and trees. Especially on large systems, be careful not to run the line too long or put too many emitters on it: the tubing has limits on how much water it can efficiently handle. Remember: running a line uphill shortens the possible run, downhill increases it.

Tip: To break up long lateral runs, center the main distribution line to create a T instead of an L. This way, if the line on one arm of the T is cut, the plants on the other arm won't be affected.

Should you bury the poly lines 2 to 3 inches in soil? There are pluses. Buried lines last indefinitely. They are less prone to disturbance by animals, children, and gardeners' tools--and the garden looks more attractive. Since buried emitters don't dry out, they're less likely to clog from calcium buildup.

But lines left on the surface are easier to install, repair, and maintain, and they're less likely to be cut by a shovel. By adding a 2-inch layer of mulch over them, you create many of the same benefits that you have with buried lines.

Choosing and spacing

the emitters

This depends on your soil (see box on page 71), plants, and type of terrain.

Calculating number of emitters. Once you know your soil type and have identified your plants, decide on the correct gallonage and number of emitters for each plant. You want to wet at least 60 percent (.6) of the root zone. Here's a simple way to figure that out. (The chart on page 71 is also a basic guideline.)

Number of emitters = the square footage of the branch spread (radius times radius times 3.14, or [pi]) times .6, divided by the wetted area of the emitter.

To determine the area of the root zone, measure or estimate the radius of the plant canopy (4 feet, for instance). Multiply the radius by itself (4 x 4 = 16), then multiply this number by 3.14 to get square feet (16 x 3.14 = 50.24 sq. ft.). Multiply 50.24 by .6; you get 30.14.

The next number comes from the box on page 71. Is your soil loamy? A 1-gph emitter wets an 11-square-foot area in loam soil; divide 30.6 by 11; you get 2.782. The plant needs three 1-gph emitters.

As a rule of thumb, use higher-gph emitters for trees and plants in sandy soil, lower ones for shallow-rooted plants and in clay soil. Also, space drippers closer together for shallow-rooted plants.

Once you become familiar with the wetting pattern of an emitter in your soil type, you can estimate the number you need fairly accurately.

Spacing emitters. Spacing is greatly affected by the layout of the plants and the beds where they're growing. In saline soils, the wetted areas must overlap at the center of the rootball. (Place the emitters close enough to overlap this area.)

If shrubs are spaced less than about 2-1/2 feet apart in a confined bed, the soil area will eventually fill up with roots. No need to design a system to suit each plant--just space the emitters 1-1/2 to 2 feet apart to moisten the entire bed.

Tip: For established trees and shrubs, a good rule of thumb is to place the emitters a third to half the distance from the trunk to the drip line.

You may have to manipulate or adjust the placement of emitters or sprays to make a design work. For example, a shrub might need one emitter instead of two because an emitter on a neighboring tree is wetting part of its roots.

Finally, you're ready

to install the system

Using the photography on page 72 as a guide, assemble valves, filters, and pressure regulator. Place a main shutoff valve after the bibb, to let you shut off the irrigation system but still use the faucet.

Wrap threaded connections with Teflon tape before attaching. Hand-tighten plastic fittings; don't use a wrench. Make sure the arrows on valves and pressure regulators point in the direction of water flow.

To soften poly tubing so it's easier to lay out, warm it in the sun for an hour or so. If the ends are difficult to insert into the fittings, dip them in warm water.

Connect the tubing (or PVC, if you use it) to the valve assembly and lay out the main distribution lines (in trenches, if you're burying them). Try to place the lines next to walls and edges of paths where they're easy to find and more protected. The pictures above illustrate techniques for installations on a slope, in a vegetable garden, and between steppingstones.

Attach lateral lines with T and elbow fittings. To attach one of these compression fittings, nick the tubing with your fingernail 1/2 inch from the end; use this mark to determine how far to push it into the fitting. If it goes in too far, it can cut off the flow of water through the pipe.

Reshape minor kinks or cut out bad crimps in the tubing. Crimps are weak spots that can eventually leak or cut off water flow.

Weave tubing in a figure 8 around shrubs. If it's on the surface, this helps hold it in place if it's pulled or raked. Hairpin stakes also help to secure it.

To conceal tubing on patios, run it under decks, benches, and other places where it won't be seen. You can wrap microtubing around posts, hide it in cracks, or run it up through container bottoms.

Try not to get dirt in the system when assembling lines and installing emitters. Flush all lines before installing emitters (open end caps and run the system for several minutes).

Different brands of emitters require different hole sizes, so select the right punch. To punch a clean hole, hold the tool perpendicular to the tubing, squeeze the tube on each side with your fingers to keep it from flattening, and then push and twist straight down. Don't take a punch out and try to reinsert it: this may make the hole so big it leaks.

Barbs should snap in snugly. If you make a mistake, insert a goof plug (to seal the hole) and try again.

When running emitters to pots and hanging baskets, either leave a 2-inch air gap between dripper and foliage or soil, or place an atmospheric vacuum breaker on the line 6 inches above the highest emitter, to prevent backflow.

To allow for root growth of trees, install emitters on J-loops around the base (see photograph on page 68). First place the lines on the rootball, then spread them as the roots grow.

Once the system is all together, flush the lines again (leave ends aboveground for future flushing), and then turn it on.

To confirm that you have enough emitters in the right places, let the system run for its normal cycle, wait several hours, and then dig into the soil in several places to check moisture spread. If necessary, add or reposition emitters.

When the checkup is finished, bury or mulch over the lines.

Plan for the future

Here are thoughts to keep in mind.

Allow for root growth. The system should be able to handle both a young plant with a confined rootball and the mature plant with its much larger and deeper root zone.

As the plant grows, you may need to add emitters. To encourage deep rooting, you can change emitters to a higher output (from 1 gph to 2 gph for trees). Or just increase flow times.

If you planted flats or sixpacks to be watered with emitters, hand-water them until their shallow roots get established. With 1-gallon plants, an emitter at the rootball will suffice. For newly planted shrubs, place one emitter on top of the rootball. As large shrubs mature, add emitters farther out on the line.

As trees expand, you need to open up the loops and add more emitters. For large trees, you may need to extend the tubing with a connector.

Remember, when you switch to drip, it will take your established trees and shrubs at least several weeks to adjust. If the plants have always been watered shallowly, begin with frequent waterings and slowly increase the intervals.
COPYRIGHT 1988 Sunset Publishing Corp.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1988 Gale, Cengage Learning. All rights reserved.

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Title Annotation:includes related article on relationship between plants and soil; drip irrigation
Date:Jul 1, 1988
Previous Article:Front to back, they did some cottage-stretching.
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