Drip Irrigation: Hard to Know, Easy to Like
Drip irrigation, of one kind or another, is the near-perfect way to water a long, narrow bed of flowers or low shrubs. It’s easier to install than sprinklers (no digging trenches) and about 15% more efficient with water. But many people have a hard time maintaining or even understanding drip systems.
The biggest question is: “How long do I leave them on,” since you can’t see the ground getting wet.
Others object to the visible tubing, although it can be covered with a mulch and some kinds can be buried. The tubing can get in the way of ordinary gardening activities, such as digging or hoeing, and a few plants that root along the stems or spread by rhizomes, don’t, because the surface remains dry.
Gardening irrigation consultant Robert Kourik has written an excellent book, “Drip Irrigation” (Metamorphic Press, Santa Rosa, Calif.; $12), and it demystifies the subject with all the details on choosing and installing a drip system. It singles out in-line emitters as the best all-round choice.
In-line emitters: For flowers or small shrub beds, Kourik and irrigation consultant Bob Galbreath of Garden Technology, Los Angeles, suggest blanketing the bed with in-line emitters, rather than using individual emitters on the ends of spaghetti tubing.
In-line emitters are built into the larger one-half tubing and are usually spaced about a foot apart. If you cover the bed with rows of tubing spaced a foot apart, you’ll end up wetting the whole bed, even if the water is barely visible on the surface because the water spreads at least 12 inches underground in most soils.
This means that the plants get evenly watered but the surface seldom gets wet enough for weeds to sprout, another big plus for drip.
You can hide the tubing under a water-conserving mulch or even bury some kinds underground. Kourik says that buried in-line drip systems must be activated everyday, even if it is only for a minute or two, or deposits in the water will clog them.
You need all of the standard drip devices at the beginning of the line: vacuum breaker, check valve, filter and pressure regulator. These are more available at stores than they were a few years ago, but you may have to look in Kourik’s book to find sources for the sophisticated in-line tubing, an unlikely find at home supply stores or nurseries.
Kourik has found that drip systems typically cost 20% to 30% more than sprinklers, “But the pay-back comes in only four years from water savings.”
None of the consultants recommended “porous tubing” drip because they found them prone to clogging, but several gardeners we know use these inexpensive soaker systems and simply replace them every few years.
Jim Worcester at Rain Bird also suggested laser tubing, which has precisely drilled holes spaced 6 or 12 inches apart. It is designed to be disposable, and he likes it in beds of annuals. Again, the idea is to blanket the whole area, but toss it out every year.
With true drip systems, fertilizing is more work. You can’t just scatter fertilizer on the ground unless rain will carry it into the soil. You must either install a fertilizer injector on the system, water the fertilizer in by hand or work it into the soil.
Micro-sprays and mini-sprinklers: These little sprays and sprinklers attach to drip tubing and put the water on much more slowly than conventional sprinklers. Different kinds vary from 5 to 20 gallons an hour , compared to conventional sprinklers that deliver 1 to 2 gallons every minute.
They are very subject to wind because the droplets are so small, and they are quite fragile, usually being mounted on top of slender plastic pipes or tubing attached to stakes. Dogs and kids can wreak havoc; however, the slender black pipes are nearly invisible in the garden, and many can be made any height you wish so they are above all the plants.
There are adapters that let you mount them on top of the sturdier standard PVC pipe.
If the pressure is very low, they will water small areas, but with even 30 pounds pressure, they cover a radius of up to 20 feet.
On the plus side, these little sprays and sprinklers are incredibly easy to set up. They must be turned on for much longer times, but they wet the ground with no puddling, erosion or compacting of the soil. They are sure to germinate every seed you sow, plus all those lying dormant in the soil.
Which is best?
None of these irrigation systems, from pop-ups to drip, are easy to design, and installation is at least some work; however, the various manufacturers have design and installation guides for sprinklers.
Which one is right for you? Consider these points and which is most important:
Save water--choose drip.
Less weeding--choose drip.
No digging trenches--choose drip.
Grow a great variety of plants, including those that spread by rooting or rhizomes--choose micro-sprays or pop-up sprinklers, maybe drip.
Need to see wet ground--choose micro-sprays or pop-up sprinklers.
Out of the way and invisible--choose pop-ups or bury drip.
Uncomplicated--choose pop-up sprinklers.
No work at all--have someone else design and install one of these systems, putting everything on a timer (but remember to adjust the settings by season, and shut it off when it’s raining).
