Ask The Droughtbusters: April 1999

Q. My company operates in a southeastern coastal city. Sandy soil is common and so are water shortages during the summer. A lot of my customers ask about drip irrigation for trees and shrubs, items that are either irrigated with sprayheads or not at all. What they are really asking is can they use one or two existing stations for drip and install the system themselves. How much should I tell them?

A. Plenty – start by telling them that each plant has a unique water requirement that can’t be met with one type of emitter. One runtime for all plants in a plant bed requires careful selection of emitters, both by flow rate and number. A big factor is the soil and how water moves by capillary action. In your case, sandy soils would require closer emitter spacing and shorter, more frequent scheduling. But “shorter” could be two hours.

If I were you, I’d explain what happened to your local irrigation supplier. Help the supplier organize irrigation training and certification classes in your area through the IA, which will supply all training materials and a qualified instructor. The cost of this training will be offset later by reducing the number of situations like you described.

Tell customers that drip system performance depends upon reduced pressure and flow. Typical public supply pressure runs 80 to 120 psi. Drip systems are designed to operate at less than 30 psi.

Pressure compensating emitters can provide a uniform flow within a pressure range, often 15 to 30 psi. If pressure is too low, you aren’t getting the expected amount of water in the given amount of time. In fact, you might not get any water to the last emitters on the line.

The flow control knob on valves is not intended to control pressure. To lower pressure properly you need a pressure reducing valve for each drip zone, or one on the lateral to all drip zones. If you design systems, think about running one lateral just for drip zones. Figure out which is a better buy, more pipe or more pressure regulators.

Also, polyethylene pipe is easy to damage by traffic, rodents, and lawn equipment. Do not run long lengths of poly pipe on the surface, even if you cover it with bark mulch. Run PVC pipe underground to points where short runs of spaghetti tubing can reach many plants. Use the same riser you would for a sprinkler head, but install a multi-outlet drip line device instead of the head. Good multi-outlet devices include screens to prevent emitter clogging. Cover the small tubing with mulch to conceal them.

By having the ability to add emitters as the plants mature, you will have more control over plant water needs. For plants like groundcovers or turf in narrow or irregular beds, use buried tubing with in-line emitters. If you filter the water entering the drip zone, you can expect five or more years of reliable use from the buried dripline. This lifetime can be extended with periodic flushing and treatment with algae control products.

Remember that drip systems have the ability to waste water just like sprinklers. Design, operation and management make them efficient. An off-the-shelf drip system is no guarantee to conserve water or to provide the right amount of water for each plant. The customer needs to ask himself, how valuable are they plants and is a $30 drip system a smart investment to protect them?

One final point – a study in Nebraska proved that water use by farmers, with the same crop in the same type of soil with the same type of irrigation system, varied by as much as 300 percent. However, the extra water used by some did not produce greater yields or better quality. Drip is a technology that can deliver the right amount of water for acceptable quality without waste, if you know what you are doing