Drip Irrigation for Great Vegetable Yields

watering-a-vegetable-garden-3By Robert Kourik

Drip = Yields

The reservoirs are full and most people are getting less concerned about irrigation this summer. Yet every year, drip irrigation can increase plant growth and produce more vegetables.

Drip irrigation can be used for the slow, gradual application of tiny amounts of water on a frequent, or daily, basis. This maintains an ideal soil moisture level, promoting more abundant foliage, greater bloom, and higher yields (by actual comparison) of produce, fruits, and nuts than those produced by any other approach to irrigation.

Research in many different climates and states invariably supports the benefits and cost-effectiveness of drip irrigation. Art Gaus, an extension horticulture specialist with the University of Missouri at Columbia, MO, has had a drip system in his personal garden for nine years. One summer, his bush watermelons with plastic mulch and a drip system produced 32 pounds in a four-by-four-foot area, compared with 9–16 pounds in the same area with conventional irrigation. He reckons a well-timed drip system “could mean a 100% increase in yields; during the droughts of 1980, ’83, and ’84, it meant the difference between having a crop or no crop at all.”

In a study of established pecan trees in Georgia, trees with drip irrigation added had a 51% increase in yields.

Michigan State University has documented a 30% yield increase in vegetable crops with drip irrigation, even in its humid, summer-rain climate.

A study in Sri Laka, in 2002, found that with chilies, water use was down 34%–50%, while production was up 33%–48%. The researchers attributed this to irrigation that kept the soil moist, not too dry.

A study in New Mexico found amazing differences in yields compared to [respectively] furrow and drip irrigation: 18 pounds versus 30 pounds with cucumbers, 69 to 156 pounds  growing Swiss chard, and 64 versus 166 pounds with green beans—to quote a bit of the study. [It is interesting to note that broccoli, Brussels sprouts, and carrots didn’t have any greater yields in these drip irrigation plots. Yet, a study at Oregon State University found a 20% increase in carrots compared to plots with sprinkler.

Required Stuff

To paraphrase the late, great comedian George Carlin, “People love their ‘stuff.’ The more ‘stuff’ the better. But where are they gonna put all their ‘stuff?’ ” Well, drip irrigation can add a lot more “stuff” to your yard. A poorly designed system can clutter your garden with cheap, breakable “stuff.” A well-designed system keeps clutter to a minimum by maximizing the effectiveness of whatever bits and pieces you use and hiding much of the system with an attractive mulch.

So, under the heading of absolutely necessary “stuff” for a good basic drip irrigation system are a backflow preventer to keep water in the hosing from siphoning back into your home’s pipes; a fine-mesh filter so the small orifices in the emitters don’t clog, a pressure regulator to keep the easily assembled fittings from blowing apart, and carefully placed lengths of black or brown hosing with emitters to control the flow of water. Important “stuff,” but not too much.


Emiters with configurations, usually in flow rates of ½-, 1-, 2-, and even 4-gallons per hoour (gph), and are inserted into ½-inch polyethylene drip irrigation hose. A hand-held tool is used to pinch a hole very much smaller than the barb’s shaft. When the emitter’s barb is inserted, the plastic hose naturally forms a tight compression around the shaft.

Punched-in emitters do have the advantage over porous hose of being able to allow more than 200 linear feet of total drip hose per valve—up to 1000 feet, providing the total amount of water emitted is less than 110 gph. An example would be 220 emitters rated at ½ gph each or fifty-five 2 gph emitters. The limit of a total flow of no more than 110 gph is to compensate for the reduction in flow caused by the friction of water moving through the extra length of hose. With more than 200 linear feet of tubing, you must use pressure-compensating emitters so that all emitters pass the same amount of water, regardless of the length of the hose.

Emitters are commonly used for what I call point-source drip irrigation, in which only one or two emitters are placed near the stem of each plant. There are both regular and pressure-compensating emitters. With regular emitters, the flow rate from one end to another [on lines totaling more than 200 feet or from one elevation to another] can vary considerably. If the total up-and-down change in your garden’s topography is more than 20 feet, you must use pressure-compensating emitters, that are designed to put out almost the same amount of water regardless of topography and length. Even though pressure-compensating emitters can cost about 50% more, when I need punched-in emitters, I always use the pressure compensating type, to make sure the flow is consistent throughout the system.

The main limitations with the use of pressure-compensating emitters is that the stem of the emitter will get brittle with age and can easily snap off during weeding, hoeing, or mulching. In a large garden, installing hundreds of emitters can injure a “weekend warrior’s” wrist or shoulder.

In-line emitters are the least well-known drip irrigation technology. In the 15 years since the first edition of this book and the writing of this revised edition, the in-line-emitter tubing is becoming more available—at least through certain retail and mail order outlets. It’s usually found at stores that supply the landscape contractors with all types of irrigation products. [At Freidman Brother’s now.] In the 35 years since I’ve used this type of drip hardware, it is in my experience, the best mix of efficiency, ease of installation, and resistance to clogging and leaking. The tubing is nearly ½-inch in diameter and comes with an emitter pre-installed inside the tubing at regular intervals.

These internal emitters utilize what is known as a “tortuous path” [See illustrsation] the water must pass through a labyrinth of right-angled channels inside the emitter before exiting via a hole much larger than that of a typical punched-in emitter. The tortuous path causes the water to form a continuous vortex, a kind of horizontal tornado, which keeps any sediment, sand or silt in suspension so it won’t settle out and clog the emitter. I used in-line emitters for Chester Aaron’s (of Occidental) 60 raised beds of garlic 15 years ago. Even with well water full of iron oxide [notorious for clogging regular punched-in emitters], I’ve found only a few clogged emitters in a thousand feet of tubing.

Another person I know actually took off the filter and pressure regulator for four years and found no clogged emitters compared to the filter and pressure regulator assembly they originally installed. A true testimony to the cleaning action of these emitters.

In-line emitter tubing moistens the soil the entire length of the line but slightly below the surface, where the bulbous-shaped wet spots come together to form one nearly continuous moist zone. The emitters come pre-installed in tubing with 12-, 18-, 24-, and 48-inch spacings [they can be custom ordered at just about any interval—for an extra fee], but the type most commonly sold to gardeners is the 12-inch interval. The emitters inside the hose are rated to dispense either ½- or 1-gph.   The cost ranges from $22 to $30 for a 100-foot roll depending on the emitter [its flow rate and whether or not it’s pressure compensating.]

Newer versions include tubing with pressure-compensating emitters at the same intervals as in the non-compensating in-line tubing and with ½- or 1-gph flow rates. I always use the kind with ½-gph emitters on 12-inch centers because they will irrigate, depending upon how long the system is left on, both sandy and clayey soils.

The benefits of in-line pressure-compensating emitters are: they are very easy to install, simple to snake around your existing plantings, suffer less clogging than porous tubing and some punched-in emitters, provide consistent rates of irrigation without regard to slope or length, have no external parts to snap off, their connectors or fittings don’t leak

betsy-dripVegetable Beds

Since I conceived a design for Preston Vineyards in 1986, I have modified the design and some of the parts. Figure __ shows my current configuration. A main line of ½-inch solid  drip hose is laid on the ground along one end of all the boxes. At the center point of each box, the solid hose in the trench is cut with hand pruners and a Spin-Loc tee is inserted with its “leg” facing up. Enough solid hose is added to come out of the ground and reach the top edge of the box, then the main line is flushed. In the center of the box, a 1-1/2-inch-square notch is cut into the upper lip of the 2- by 12-inch board. This permits the drip hardware to pass into the box without visually breaking the line of the end board. The following series of parts is assembled to allow for speedy and convenient removal of the drip irrigation harness from the box:

1—Add a Spin-Loc elbow to the top of the solid drip-hose riser coming out of the main line. Trim the riser so that the elbow will pass its drip hose through the notched area.

2—Insert a three-inch length of solid drip hose into the end of the elbow that is parallel to the ground.

3—To the end of the short piece of solid drip hose, add a Spin-Loc x male-hose fitting. These are sometimes sold in a set with a female hose thread cap as end-closures for drip lines. Just save the cap for that wonderful collection of parts kept in a large coffee can and labeled “Plumbing stuff I have no idea if I’ll ever use but I’m too cheap to throw away.”

4—To the x male-hose fitting, add the female end of a metal ball valve hose shutoff. This will allow you to turn off certain beds if nothing is planted in them or remove the harness from one bed while other beds are being irrigated.

5—Some hose shut-off ball valves have little holes built into each side of the valve. Use these holes to tap some small nails into the base of the wooden notch to secure the plumbing assembly, or use two screws with washers to hold the ball valve in place. Be sure the male hose threads of the hose shutoff extend beyond the wood, toward the inside of the box.

6—Next, add a Spin-Loc swivel x compression tee to the x male-hose fitting of the shutoff-valve. The “leg” of the tee has a swivel hose fitting, and the “top” of the tee has two Spin-Loc fittings for in-line pressure-compensating emitter tubing.

Now you can use in-line pressure-compensating emitter tubing to finish the harness, which rests on top of the soil in the bed. I usually recommend the in-line tubing with ½-gph emitters on 12-inch intervals because it works on both sandy-loam and clay soils, depending upon how long you run the system. One- and two-gph emitters, with their higher flow rates, work better in very sandy soils because the greater volume causes the water to spread more horizontally underground. This makes for a fatter carrot-like shape to the wet spot beneath the surface of the “bed” and distributes water more evenly to the roots. For a three-foot-wide bed with a fairly loamy clay soil, you’ll probably need only two lines of tubing running the length of the box. A four-foot-wide bed may need just three lines of tubing. If you’re growing a crop that is planted close together, such as garlic, beets, turnips, or small European butter lettuces, you may want to have four lines per box to ensure adequate irrigation. It’s best to put together a trial system first to see how the harness configuration works with your soil. In any case, to get the spacing [in inches] between each line across the width, divide the bed’s width [in inches] by a number that is one larger than the number of lines you’ll be using.

From the swivel tee, next to the shutoff-valve, add the appropriate lengths of in-line tubing to reach the next fittings on the main header that runs the width of the bed. For the outer two lines, add Spin-Loc elbows. For any lines other than the outside ones, add tees at the appropriate intervals. Always remember to leave the length of these lines loose and not firmly staked, to protect the fittings as the tubing shrinks in the fall.

Flush the system. Close the ends of each line in all the vegetable beds with an end cap. Mulch to disguise and protect the tubing, and you’re ready to grow some food.

Getting a Grip on Your Watering Schedule

The City of Santa Monica is one of the most proactive cities when it comes to irrigation water conservation. They require any plant from a one-gallon container or bigger to be irrigated solely by drip irrigation. [They also limit lawns in new homes to 20% or less of the property.] They are one of the municipal pioneers that require Weather Based Irrigation Controllers [WBIC].

WBICs are rapidly carving away at the cost of such controllers while, at the same time, adding more refinements for precision irrigation based on your yard—not even relying on a governmental weather of the state of California.

The irrigation industry’s organization for the country is, simply put, the Irrigation Association. They have developed standards for testing irrigation controllers and timers called Smart controllers. Smart irrigation controllers are defined by the Irrigation Association as “… controllers [that] estimate or measure depletion of available plant soil moisture in order to operate an irrigation system, replenishing water as needed while minimizing excess water use. A properly programmed smart controller requires initial site specific set-up and will make irrigation schedule adjustments, including run times and required cycles, throughout the irrigation season without human intervention.”

Such controllers help deal with the fact that 30%–300% of irrigation water is wasted in residential landscapes. [Outdoor watering uses up to 60% of the total household water usage.] Not all Smart controllers are the same. Some are much more efficient than others. Through independent testing the Irrigation Association has come up with a higher standard. The official standard of excellence uses what is called a SWAT controller—Smart Water Application Technologies™. Not all WIBCs pass the test. The list below shows some of the WBICs that have passed the SWAT test.

Manufacturer          Model

Alex-Tronix                  Enercon Plus 4-24

Alex-Tronix                  Smart Clock SMC6

Aqua Conserve            Aqua ET-9

Calsense                       ET2000e

Cyber-Rain                  XCI      System

ET water Systems      ETwater Smart


Bon Appetite

For more education on gardening – irrigation – and some truly fascinating information – please read Robert;s Blog (http://robertkouriksgardenroots.blogspot.com) and purchase Robert’s numerous books: http://www.robertkourik.com

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