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Drip Irrigation: A Smarter Way to Water

By Skip Richter
Contributing Editor

I don’t have a crystal ball, but there are a few things which I can be quite sure of when it comes to the future. Texas summers are going to be hot, and mostly dry. Our population is rising and the quantity of available water is not. So more laws and ordinances will be passed in the years to come, further restricting how and when water is used. And, the price of water will go up.

This means that more efficient watering systems will be an important part of our landscapes. In fact they already are. We have had the technology to get more out of every drop of water we apply to gardens and landscapes for decades now, but like many good ideas, for one reason or another this technology just hasn’t fully caught on. While there are several great gadgets and techniques that will help us get the most out of our watering dollar, in this article I want to focus on drip irrigation.

I’ll bet every reader has heard of drip irrigation and even understands how it works. I’ll also bet that most readers don’t have a drip system in their garden or landscape. Well, I understand. I was a late adapter myself. Perhaps we feel the cost is prohibitive, maybe we are intimidated by what seems too technical for the average do-it-yourselfer, or we may just not be convinced that it really works. Well, it’s not, it isn’t, and it does! Read on and I’ll explain.

Why Drip Irrigation?
Drip irrigation is quite simple. It basically involves delivering water to various parts of the landscape through a series of plastic tubes and applying it right where you want it through emitters that slowly apply it onto the soil surface.

Drip offers a number of advantages over sprinkler irrigation. It is an efficient way to water. More than 90 percent of the water you apply through drip irrigation will be available to plants compared to only 50 to 60 percent with sprinklers.

A drip irrigation line applies water directly to the soil rather than slinging it through the air and onto the foliage where much is lost to evaporation. Sprinklers wet the entire garden area so walkways and areas between the plant rows get wet, too. This off-target watering wastes water and increases weed problems. You can walk through your garden while irrigating with drip and have no muddy pathways. In fact, I like to work in the garden while my drip system is running. It’s kinda cool to watch!

Because water is applied slowly with drip, it is able to move into the root zone without runoff and the soil surface is not subject to erosion or crusting as with sprinklers. Because the foliage is not wet every time you water, leaf diseases are minimized.

Drip irrigation is by far the most effective and efficient way to apply water to garden and landscape beds or to fruit trees, vines and bushes.

Parts of a Drip System
Drip irrigation systems in commercial orchards, truck farms and extensive landscape installations can be rather complex, but in a basic home garden system they are quite simple.

The basic system for hooking up to a garden faucet has 5 components: a backflow preventer, a pressure regulator, a filter, delivery tubing and the drip tubing.

Backflow preventers are especially important if you plan on occasionally fertilizing through your drip irrigation system. They prevent water from moving from the drip system back into your water lines should a drop in pressure occur in the water line.

The pressure regulator reduces the pressure of your water line down to an appropriate working pressure for the drip emitters in the drip line, usually about 10 to 25 psi, depending on the type of emitters selected. Without it the system won’t work properly. The filter catches sediment such as sand or chunks of lime flowing through the water lines to prevent them from clogging the emitters in your drip system.

The delivery tubing carries the water from the faucet to the garden beds and the drip tubing applies the water where you want it. There are several types of drip tubing and emitters. These can be divided into two basic categories: Tubing into which individual drip emitters are placed and tubing that comes with emitters already in place.

With the first type you purchase the tubing, typically 1/2-inch poly tubing, and the emitters of your choice. Then you punch holes in the tubing where you want the emitters to go and pop one of the barbed end emitters into each hole. The second type of tubing either has tiny precut slits from which the water drips or emitters that are preinstalled inside the tubing.

There are so many different options with each type that there is not room in this article to delve into all of them. Instead I’d like to offer my opinion about the two simplest and best choices for someone starting off installing their own drip irrigation system for a vegetable garden or ornamental bed: drip tape and in-line emitter poly tubing.

Drip tape or T-Tape is an inexpensive, relatively thin-walled type of tubing with emitters in the tubing. This type of tubing is great for straight garden beds but doesn’t curve around corners. I use it in my vegetable garden beds, placing two drip tape lines down each bed. It is easy to attach to the 1/2-inch poly delivery tubing with special barbed connectors that pop into holes you make in the delivery tubing.

The emitters in the drip tape are a special design where the water first flows through a zig-zag pathway before exiting the tubing. This is referred to as a “tortuous path” or “turbulent-flow” emitter. This design reduces pressure fluctuations somewhat so that the amount of water applied stays fairly consistent all the way down the length of drip line.

In-line emitter poly tubing is constructed of 1/2-inch poly just like the delivery line. However, it has special “tortuous path” emitters installed inside the line as it is made. On the outside all you see is a small hole where the water drips out. This type of line can be bent gradually to go around corners, making it my favorite choice for landscape beds. For tight corners there are “L” and “T” type fittings as with all other types of drip irrigation line.

These “tortuous path” emitters are not truly pressure compensating emitters but do provide some compensation for variations on pressure. If you have a situation where drip lines are going to drop several feet in elevation over the course of the run, there are pressure compensating emitters that can be purchased and placed into poly tubing.

With both of these types of drip tubing you can choose from a range of predetermined emitter spacings. Depending on the type of line available, spacings include 6”, 9”, 12”, 18” and 24”. I find that 12” spacing is best for most home garden and landscape applications.

Building Your System
Building your own basic garden drip system is really quite simple. In fact, it is rather like playing with Tinker Toys! Start by doing a little shopping for a good supplier. While drip irrigation supplies are widely available, including through some home stores, I suggest you consider not only price but also the variety of products offered and whether or not the seller provides guidance or customer assistance. Local garden centers and online sources are good choices to consider.

Purchase a backflow preventer that can be attached to an outdoor faucet. I actually start with “Y” or multi outlet splitter attachment so I can still attach a garden hose to the faucet when I need to. The backflow preventer is attached to one outlet on the splitter. After the backflow preventer, attach the filter followed by the pressure regulator. For small home drip systems a screen type filter works fine.

Next attach the poly tubing used for delivering the water to the garden area. In my system I purchased a series of inexpensive valves for use on the poly tubing so I can control which garden areas are being watered. The poly tubing can be left on the soil surface and covered with mulch or buried a few inches below the soil to get it out of sight, if you like.

At the garden the particular type of drip tubing you choose takes over to provide the water to the plants. There are fittings for each connection between various types of tubing, as well as “L” and “T” fittings, unions for joining two sections of tubing and end flush connections that allow you to flush out the lines periodically. This is where some help from your supplier can make it easier to know how many of which types of fittings to purchase. Most fittings are attached to the tubing by slipping the tubing over a ridged nipple and then screwing a covering ring down over the outside of the tubing to hold it tight.

Setting Up Your System
Start by planning out where you want to install drip tubing and where the nearest faucet is located. Determine how much delivery tubing you need and how many feet of drip tubing are required. Buy a little more than you think you need…trust me.

Emitters generally put out either 1/2 or 1 gallon per hour, although other rates are available. Depending on which type you purchase and the distance between emitters, the flow in a particular line will vary considerably. As a general rule of thumb, figure on an outdoor faucet putting out 5 gallons per minute, which is 300 gallons per hour. Once you put this through the filter, pressure regulator and into the 1/2-inch line, you can conservatively figure on about 120 gallons per hour. This would mean that a line will supply about 120 emitters that drip 1 gallon per hour each or 240 emitters that drip 1/2-gallon per hour.

As a general guide you don’t want to make runs that are longer than about 250 feet from the source. If you want to split the line at the source and run it two ways each could be up to a 250 foot run as long as it doesn’t supply much over 120 gallons per hour.

Add up the flow rate for all the emitters on series of lines to ensure that it doesn’t exceed the maximum flow rate. On my home garden system I have set up several valves that enable me to run one or two such “zones” at a time. Keep in mind that all these are general guidelines and a number of factors will cause variations in results.

Be prepared to experiment a little. There are some handy additions such as poly tubing valves that can be added to allow you to turn sections off and on when an entire length of run proves to be too long, or your water supply doesn’t provide the rate of flow you thought it would. Remember, this is like Tinker Toys; so it’s no problem to take something apart and redesign a section!

While some types of drip line can be buried, I prefer to keep mine on the surface to minimize clogging and entry of roots into the emitters. That way I can easily check to make sure the line is working and fix any problems. I do however cover the line with mulch in some areas for personal aesthetic preferences.

Other Systems
I’ve focused on a couple of simple types of drip tubing in this article. There are many more options well worth considering. Orchards can be irrigated with drip but can also be watered very efficiently with microsprayers or microsprinklers which spit out droplets in a large circular area down low to the ground to minimize evaporative losses. There are automatic valves and timers that can be added to make a system easier to use, even when you are on vacation!

If you have a fairly large property or special circumstances such as a significant slope across the property, it is probably best to hire an irrigation professional to design a system for you. But for most gardeners a simple do-it-yourself system is an easy-to-build weekend project well worth your time and money.

This year give drip irrigation a try. Start small, perhaps with your vegetable garden or a set of color beds in the landscape. You’ll save on water for years to come while saving time dragging hoses and sprinklers. Best of all, your garden and landscape plants will look and perform their best!

ADDITIONAL INFORMATION
Efficient Use of Water in the Garden and Landscape:
http://aggie-horticulture.tamu.edu/extension/homelandscape/water/water.html

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