Lately, there hasn't been a need for irrigation in the Lowcountry. Not yet, at least. Eventually, the skies will clear and the rain will go away to come back another day. Here are some tips to make sure your irrigation system is working properly.
ControllerThe irrigation controller is a glorified timer. The simple controllers are programmed to start irrigation on specific days for a set period of time. They're cheap but need to be reprogrammed as the weather changes to avoid over- or under-watering. A simple controller can be outfitted with a sensor to turn it off during wet weather.
Smart controllers, on the other hand, calculate the daily water requirements and automatically adjust the program. They are more expensive but rarely need adjustment.
However, you'll still need some information to accurately program your controller. The number of minutes per zone depends on a variety of factors, starting with the type of sprinkler.
SprinklersSprayheads distribute water in a fan-like pattern in small areas such as a side yard. They typically throw water 15 feet or less.
The irrigated area around the sprinkler is referred to as the arc: quarter arc (90 degrees), half arc (180 degrees), or full arc (360 degrees).
Nozzles are purchased separately from a sprayhead body. Variable arc nozzles can be adjusted to any arc.
Sprayheads are typically referred to as “pop-ups” because they pop out of the ground when running and retract below the turf when off.
A pop-up sprinkler, however, is any type of sprinkler that does this, but sprayheads seem to be the ones most associated with the name.
Sprayheads are susceptible to misting when run at pressure above 30 psi.
Purchasing pressure regulating sprayheads will prevent high pressure during operation.
Consider replacing sprayhead nozzles with rotary nozzles.
Rotary nozzles efficiently distribute water in multiple streams that reduce drift and runoff.
Rotors are the larger sprinklers that spray a single stream of water that goes back and forth covering a large area. The rotor sprinkler, not the nozzles, is adjusted to cover the appropriate arc.
Each rotor sprinkler comes with an assortment of nozzles. Proper selection of a nozzle is important to match the amount of water with the area of coverage.
For instance, a No. 1 nozzle can be inserted in rotors covering a quarter arc.
Rotors set to cover a half arc will require a No. 2 nozzle because they are covering twice as much area and, therefore, require twice as much water.
A full arc would require a No. 4.
Precipitation rateOnce you have identified your sprinklers, it's easy to measure precipitation rate. Start with 12 catch cans.
A catch can may be anything with straight sides and a flat bottom such as a coffee can. Place catch cans throughout a zone and run the water for 30 minutes.
Measure the depth in each can with a ruler.
Precipitation rate is measured in inches of water delivered per hour.
If you take the average of the above test and double it, this will give you the inches per hour.
Sprayhead precipitation rates tend to be much higher than rotor sprinklers.
MinutesArmed with this information, you can manually set the minutes on your controller. In the summer, we lose about 0.2 inches of water from the soil daily.
If you water every two days, you would accumulate 0.4 inches of water loss that needs to be replaced. To figure how many minutes it would take each zone to distribute this amount of water, simply divide 0.4 by your precipitation rate and then multiply by 60.
UniformityIf you really want to geek out, use the catch-can data above to measure uniformity — how evenly water is distributed. Get the average of the lowest four catch cans and divide by the overall average.
A 100 percent is perfect uniformity but unlikely.
In most situations, 70 percent or higher is considered good.
If your uniformity is low, it's time to evaluate nozzle selection, arc adjustment and sprinkler placement. Poor uniformity can lead to over- or under-watering.
Tony Bertauski is a horticulture instructor at Trident Technical College. To give feedback, email him at firstname.lastname@example.org.
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