Drip Irrigation

By Erik Knutzen
Category: Gardening
Time Required: A Few Hours
Difficulty: Easy

Most vegetables prefer soil that’s neither soggy nor dry, and earthworms and beneficial microorganisms do too. When there’s too much water, these organisms drown. Too little, and you find yourself with dead plants and a reputation as a “brown thumb.”

How much is too much, and how little is too little? How often should you supply water, and how can you remember to do so?

Drip irrigation answers these dilemmas, giving plants the perfect amount that they need to thrive, and saving water at the same time. Irrigation also keeps water off the leaves of the plants, preventing nasty maladies like leaf mildew, and you’ll suffer fewer weeds by delivering water only to the plants that you want to grow.

The chief drawbacks to drip irrigation are cost, the use of plastics, and the time and trouble for installation and maintenance. For these reasons, I believe that drip irrigation is best reserved for your vegetable garden. For the rest of your yard, try to find plants that are adapted to your climate and don’t need supplemental watering.

In this article I’ll explain how to assemble a typical layout to water a vegetable garden in a raised bed of quality soil.

The array of tiny plastic drip irrigation parts and supplies can seem confusing at first, but the principle is simple: you’re simply piecing together a stretch of hose that leaks.

The materials listed below are for a 4′×8′ raised vegetable bed. All the parts recommended for this project have hose threads.

Drip Irrigation 101

Hose Threads vs. Pipe Threads

A word about the two types of threads you’ll encounter with drip irrigation parts. Hose threads, used on garden hose and outdoor faucets, are more widely spaced than pipe threads. Drip irrigation parts may have either hose threading or pipe threading, the latter often being identified as “NPT,” referring to the National Pipe Thread standard. If you try to attach a pipe thread to a hose thread, you’ll strip the threads.

Teflon Pipe Tape

To prevent connections from leaking, prepare them with teflon pipe tape. Before joining two threaded parts, wrap the tape around the male thread in the same direction that the second part will turn when you attach it. Hand-tighten all plastic connections; a wrench can damage the delicate threads.

Parts
/
Tools

Backflow preventor
Coupler fittings
Dripline
Elbow fittings
End fitting
Goof plugs
Hold-downs
Hose barbs
Hose beginning
Hose Y connector
Mainline tubing
Misters
Pipe tape
Pressure regulator
Stakes
Timer
Valves
Y filter

Hole punch
Scissors or knife
Thermos

Steps

Step #1: What are 3 sections of a drip system?

A simple drip irrigation system consists of 3 sections: the parts near the faucet, which I’ll call the “headworks”; the mainline tubing; and the parts that drip, which I’ll call the “drippy parts.”
The headworks perform 3 tasks: reducing water pressure, filtering your water supply, and turning the system on and off. The mainline tubing distributes the water to your vegetable bed, and the drippy parts drip, creating localized volumes of moisture beneath the soil. For your raised vegetable bed, you’ll lay out parallel lines of emitter tubing to create a grid of evenly moist spots across the bed, and you’ll add some misters for starting seeds.

Conclusion

Planting

Once you’ve installed your drip system, turn it on before you plant. Note the irrigation pattern at the surface and, after running the water for at least ½ hour, dig down and take a look at the underground moisture pattern.

If you’re transplanting seedlings, you’ll need to make sure to place the roots so that they pick up water from the dripline. Plants with larger roots, such as tomatoes, can be placed farther from driplines; carrots and beets need to be placed closer. But all plants need moisture, and especially when dealing with small seedlings, beware of dry spots at the surface of the soil.

Mulch Mulch Mulch

Once your seedlings are a few inches tall, apply organic mulch in the form of leaves, finished compost, straw, grass clippings, or wood chips. Mulch conserves water, makes your plants healthier, and protects your drip tubing from UV sunlight damage. Mulch ain’t optional — if you want healthy plants you need to mulch!

Watering: When and How Long?

Many variables determine when and how long to water: temperature, humidity, root depth, and hours of sunlight, to list a few. For most mature vegetables, you need to moisten the soil to a depth of 2'. Younger vegetables require less.

One objective way to determine whether you’re watering long enough is to run your system and simply dig a hole and see how deeply the water penetrated. Despite a lot of advice to the contrary, recent research indicates that frequent light watering is better than infrequent deep watering, but this is a highly divisive topic among gardeners. Depending on the time of year, the heat, and the humidity, you’ll probably need to run your drip system 10–40 minutes each day. Plants prefer to be watered in the early morning hours.

Maintenance

Check your system while it’s running, at least once a week. Occasionally an emitter or other connection will pop out under pressure, or be kicked out by kids or dogs. You’ll also need to replace the battery in the timer periodically.

Take time to unscrew the cap on the bottom of the filter, and run the water to flush it out.

Having an automatic system is not a license to ignore the garden. Bad things happen — pests and bugs, in particular — when you don’t pay attention to your veggies. Go out and visit them. To prevent your plants from getting waterlogged, turn off the system during rainy spells.

If you live where the ground freezes in winter, you need to protect your drip system from ice damage. You need to bring in the headworks, any valves, misters, and emitters. Mainline tubing can be left in place, but should be drained or blown out with an air compressor. Then cap the beginning of the mainline tubing, or tie a plastic bag around the opening. Fittings are especially vulnerable to bursting, so make sure you lift each one to drain out the water.

Critters

Gophers and some breeds of dogs are notorious for treating driplines as water-filled chew toys. In a raised bed you can prevent this by lining the bottom with hardware cloth, which is actually a wire mesh.

Going Bigger

For larger plantings, get what farmers use: T-Tape or similar drip tape. Your headworks assembly will be the same, with the exception of a lower-pressure regulator. You’ll still use ½" mainline tubing, but the fittings for T-Tape are slightly different. T-Tape is a specialized product you won’t find at a big box store, so I recommend getting a kit from an online supplier that will have all the parts you need.

While less durable, drip tape is more economical than ½" dripline. For small vegetable plots the ¼" dripline makes more sense, since, unlike drip tape, you don’t need to get it in large quantities.

This project first appeared in MAKE Volume 18, page 72.