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HOMEGROWN Life: How to Install Drip Irrigation

6/3/2013 1:15:00 PM

Tags: drip irrigation, urban farming, FarmAid and Homegrown.org

irrigation layoutPart of my day job description includes putting together construction documents on how to install drip irrigation. Usually these documents are for huge sites with extensive systems involving thousands of feet of piping, dozens of valves, and sometimes multiple controllers.

You’re probably scratching your head trying to make sense of what you just read. That’s OK because the typical home garden is not going to require all of this fancy talk, but it will require a few necessary items to work well.

Click here for a larger version of the image at left.

Choosing Your System

I like to set my irrigation system and forget it, meaning I really don’t want to think about watering that much. Of course, having a garden that takes several hours to water every other day is exactly the reason I don’t want to think about it. But even with smaller gardens, you might want to consider drip irrigation. Sometimes life gets busy, and you might not be able to water for a few days. If you had automatic irrigation, you wouldn’t have to worry about losing the garden you had spent months nurturing.

I’m also of the mind that you should have a system even if you don’t need it. This was highlighted last summer with the severe drought in the Midwest. My mom, who lives in Ohio, depends on summer rains to water her garden, but last year the rains never came. The heat did, though. She had to spend large amounts of her time  watering by hand just to keep everything alive. When you don’t need automatic irrigation, you can just turn it off. But when you do need it, it’s nice to be able to turn it back on and let it do its thing.

With so many different types of irrigation, how in the world do you choose one? My first word of advice is to put down the preassembled garden drip irrigation kit at the big box store. Every garden site is unique, and those kits do very little to accommodate even the average one. Second, you’ll need to figure out if you want drip irrigation or overhead irrigation. (I won’t be covering the latter here; more on my preference for drip below.)

I recommend drip for several reasons. First, it is low flow, and the water goes directly on the soil at the rate the soil can absorb it. This reduces evaporation and eliminates drift from wind. It also reduces fungal diseases that can be caused by overhead watering, and it’s less likely to cause puddling and soil erosion. In addition, you’re less likely to have weeds when you control where the water is going, since weeds have a tendency to congregate at the water source rather than spreading out across your entire bed. The downside of drip, however, is that it can be clunky to handle and gets in the way of digging, hoeing, and raking the soil. Also, it doesn’t last as long as overhead, which is generally hard pipe that’s buried, and has to be checked over thoroughly before every season. To me, however, the savings in water and money are well worth these minor headaches.

Designing and Installingirrigation in garden

You will either need to draw up a site plan of the area you want to irrigate or get some construction marking paint (spray paint that can be applied when the can is upside down, usually available in fluorescent colors). The main purpose of this is to find out how much PVC irrigation pipe you’ll need between your water source and the places you want to water. Generally, the pipe only needs to run to the end of each bed that’s closest to your water source. Rainbird, a popular irrigation supply company, has some design manuals you can use to help with your irrigation layout.

Stick with 3/4-inch schedule 40 PVC pipe unless you’re planning to have a really large area on drip or you’re using spray. Then you’ll need to do pressure loss calculations, but I’m not going to go into that here (two words: advanced math). Pipe is pretty cheap, so if you purchase more than you need, which you will, you won’t break the bank. In addition to the pipe, you’ll also need joints (elbows, tees, 4-way, couplers, et cetera). This is why a drawing is helpful. Keep in mind that any turns in the pipe usually will have to be at 90 degrees.

The photo above shows how we set up our valves. The valves are what turns the water on and off automatically; there’s a manual switch, as well. The valves are connected by low-voltage wire to an irrigation timer, also known as a controller, located in our water tower. When you enlarge the picture, you can see the wires that will connect on the top of the valve (they haven’t been hooked up yet in this photo). If you have just a few raised beds, you’ll probably need only one valve. We have three different watering zones—fruit trees, vegetable beds (we need two valves due to water-pressure loss), and drought-tolerant landscape—all of which require different watering schedules, which is why we need four valves for our backyard.

It might look complicated, but once you have all of the parts you need, it’s really not. Everything goes together rather quickly. In my opinion, the hardest part of installing irrigation is digging the trenches for the pipe and electrical wires.

For the threaded joints, you’ll want to purchase plumbers/Teflon tape: a thin, relatively stretchy white material that’s not sticky to the touch. You’ll use this to wrap the threads in the same direction you’ll screw on the fitting. This tape fills in any gaps in the threads, sealing it from leaking. Wrap it around about three times but don’t let it extend past the end of the threads, as it can clog your system if a small piece breaks off. For the PVC slip joints, you’ll want to get pipe cement and primer. Some people claim you can skip the primer, but that’s only true for systems that won’t be pressurized. With drip systems, the lines will have pressure when they’re on, so make sure to use primer first; otherwise, you’ll end up with a lot of leaks that you can’t always fix. Primer is generally purple in color. You apply it first to the inside of the connector and to the outside of the pipe. Allow it to dry a bit. Then apply the cement in the same fashion and insert the pipe into the connector. It should have a firm hold and finish connecting within a few minutes, but don’t plan on running water through your system for at least 24 hours, giving the joint to cure.

Now you’ll want to run pipe to your beds. Connect the pipes with female slip joints and cement. I prefer to locate the pipe riser for each bed on the outside of the bed, although some folks prefer to put them on the inside. If the bed is already in place and filled, you’ll have to put it on the outside. The photo at left shows what you’ll need for each bed. The ball valve is important because it allows you to turn off irrigation to individual beds when a given bed isn’t in use. I like to use the threaded gray risers, as they contain carbon to help make them more resistant to UV. You can use PVC, though, if you want to. Just remember that if you use the threaded pipe, you’ll need elbows, with one end being threaded.

Now that you’ve got water to your beds, you’ll want to get the dripline down in your bed. There are several options as far as the types of line you can use. I personally like dripline with inline emitters because it’s easier to handle. You can get this in 1/2-inch and 1/4-inch sizes. For each of these sizes, there are different emitter spacings within the line. The 1/2-inch dripline’s smallest spacing is 12 inches, which might be too far apart for vegetable beds. The 1/4-inch size comes in 6-inch spacing, so you might want to go with that. Some people like to use those porous soaker lines, which look like black spongy material that weeps water when turned on. If you have hard water or even just well water, this type of line clogs really easily, and you’ll need to replace it before the season is over. (Trust me, I’ve had to do this.) The inline emitter dripline uses turbulent flow to help keep the emitters from clogging.

irrigation drip tapeAnother option is drip tape. Drip tape is inexpensive and puts a good amount of water down in a relatively short time frame. Unfortunately, it doesn’t last long. By our second season, we spent a good portion of our time repairing blown sections of it. It also requires a much lower water pressure to run correctly, which requires difficult-to-find pressure regulators.

Once you figure out which type of dripline you want to use, you’ll need to lay out how you want to water it. I prefer to run the water source on the end of the long side of the bed versus the center of the short side. From the water source, you’ll run 1/2-inch poly across the short side and then cap it. At every 6- to 9-inch spacing (spacing is according to your personal preference and also depends on the width of your bed) you’ll insert a barbed 1/4-inch tubing connector. There’s a poly tubing hole punch gun that makes this job much easier. Connect 1/4-inch dripline tubing to the barbed connector and run it to the end of the bed. Crimp the end and stake it down. You can buy end clamps or just use zip ties.

One more thing you’ll need to consider: When dealing with poly tubing, you want to use either universal fittings or fittings that are the same brand as your tubing. Different manufacturers vary the size of the tubing ever so slightly, so fittings from one manufacturer will not work on another’s tubing unless it’s truly universal. The links in the following list are meant to give you an idea of what you’re looking for. Since I’ve included different brands and sources, the items don’t necessarily all work together. Your best option is to purchase everything from the same store, which generally will offer compatible parts.

Click here for larger version of drip tape chart.

Basic Supplies for Automatic Drip Irrigation

Controller/irrigation timer

• Sprinkler wire with wire splice connectors

• Antisiphon valve with atmospheric vacuum breaker and pressure regulating filter

• 3/4″ PVC pipe

• Various 3/4″ PVC connectors: couplers, elbows, tees, risers, adapter

• Teflon tape

• PVC primer

• PVC cement

• Supplies to connect to water source

• 3/4″ ball valve (one per bed)

1/2″ poly tubing compression adaptor (one per bed)

1/2″ poly tubing

• 1/4″ dripline

Punch gun

1/4″ barbed connectors

End clamps

Stakes

A Word on Controllers

With controllers, you can go cheap or you can go expensive. Either way, it probably will be your most expensive piece of irrigation equipment. The more costly a controller is, the more features it will have, such as being able to attach rain sensors, soil moisture sensors, or more programs and stations. The one I linked to above is the one that I own. I’ve been very happy with it. It has a rain delay and a rain-shutoff switch so I can turn it off during the winter. When it’s time to run it again, it saves all of my previous programs. The programming is relatively easy to figure out, as well.

One thing I will caution you against is getting battery-operated controllers that double as valves. In my opinion (and experience), these are not reliable and go out regularly. The worst is when you’re on vacation and the battery goes out with the valve open. Yeah, this happens more often than you’d think.

My friends in college used to call me a Renaissance woman. I was always doing something crafty, creative, or utilitarian. I still am. My focus these days, instead of arts and crafts, has been farming as much of my urban quarter-acre as humanly possible. Along with my husband, I, Rachel, run Dog Island Farm, in the SF Bay Area. We raise chickens, goats, rabbits, dogs, cats, and a kid. We’re always keeping busy. If I’m not out in the yard, I’m in the kitchen making something from scratch. Homemade always tastes better!

This post originally appeared on HOMEGROWN.org.

ALL PHOTOS: COURTESY OF RACHEL



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