Wednesday, June 19, 2013

Drip Irrigation: How Long Do I Water?

     90% of all plant problems are water related, either too much or too little. Compounding the problem: gardeners who are operating a drip irrigation system but using a sprinkler mentality.

     Callers to the radio show, after describing a plant problem will be asked: "How are you watering that plant?" More often than not, if the answer is, "drip irrigation", they will follow that with, "And I run it for five minutes a day, everyday."
And therein lies the problem.

     A drip irrigation system puts out water much slower than a sprinkler system, usually a gallon or two an hour versus a sprinkler system's output of a gallon or two A MINUTE.

     In five minutes, a 1 gallon per hour (gph) drip emitter will put out about 10 ounces of water...slightly more than a cupful. Not only will that pittance of water not saturate the width of the plant's root zone (which can extend beyond the canopy of the plant), it won't penetrate more than an inch or two. And then not stay there very long.

     What happens to a plant with a shallow watering program? The roots stay very near the surface, where they are more subject to drying out quickly. This boom and bust cycle stresses the plant, opening up the possibility of disease and insect invasions.

     With a drip irrigation system, don't think "minutes". Think: "hours". And water deeply, but infrequently (once or twice a week).  

Your goal is to apply enough water to penetrate the soil to a depth of at least 8 inches, preferably more. The day after you water, either dig down 8 inches by hand or with a soil sampling tube; or, stick a moisture meter down to that depth to determine if the soil is moist (not dry, and not soggy). Battery-operated soil moisture meters (such as the yellow one, pictured on the right) tend to have a longer life.

In our raised bed vegetable garden, the summer watering regimen is with an inline drip irrigation system (1 gph emitters along the line, spaced 12" apart) which is run twice a week, six hours at a time. Your weather, soil type, slope and crops may need a slightly different watering schedule. In our 4'x20' raised beds, three inline emitter lines run the length of each bed. The lines are spaced 18" apart.

Consider using microsprinklers or sprayers to thoroughly wet the root area for trees and shrubs. These put out more water, usually between 8 and 20 gallons per hour. We have these on our shrubs and fruit trees, and during the summer will run them for about an hour, once or twice a week, depending on how hot it is.

     The other part of the drip irrigation equation that a lot of gardeners miss: not enough emitters for the plant. Placing one emitter next to a new tree or shrub is not enough. Remember, plant roots tend to grow out horizontally. Emitters should be spaced evenly around the tree or shrub, in a circle, halfway between the trunk and the outer canopy of the newly installed plant. The spacing between the emitters will depend on your soil type: for sandy soils, use a 12" spacing; for heavy clay, 18-24" spacing. Add emitters towards the outer canopy of the plant as the plant grows.

• Soaker hoses need maintenance, too. Flush them monthly. The Dramm soaker hose, pictured here, is the most reliable, even-flowing soaker hose I have ever used.

A great online tutorial of drip irrigation: the Dripworks website. This site has helpful tips and videos that can help beginner and pro alike solve their drip irrigation and yard watering woes.

     The Dripworks catalog is also great resource for anyone tackling the problems associated with drip irritation...uh, irrigation. Just thumbing through the catalog can give you several "Aha!" moments for improving your own yard watering procedures, especially if you are looking to replace your residential sprinkler systems with a drip irrigation system, which can work with your existing automatic sprinkler system control box.