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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Friday - June 29, 2012

From: Austin, TX
Region: Southwest
Topic: Watering
Title: Drip irrigation and uneven distribution
Answered by: Nan Hampton and Andrea Delong-Amaya

QUESTION:

Subject: Drip irrigation and uneven distribution. Iíve installed drip irrigation in an area of mature shrubs (St. Johnís Wort) in Austin. These have previously received about ĺ inch of water once a week from an oscillating sprinkler, so the water was uniformly applied. Iíve placed four of the new drip irrigation emitters within the 7-foot diameter drip line of each shrub. Because each emitter saturates only about a 20-inch diameter, the water now is not applied uniformly. Even if I provide the same amount of water to a shrub as before, will the uneven distribution of water within the root area pose any problem to the shrub, particularly premature browning or uneven growth?

ANSWER:

Installing a drip irrigation system is a very wise move on your part since the City of Austin Water Utility managers are considering allowing homes with drip sprinkler systems to be allowed to water any day at any time and to not have to comply with the officially-assigned watering day.   Installing the drip sprinklers is especially wise since they deliver water to the roots and not into the air where runoff can occur or much of the water evaporates before it can reach the roots.

To answer your question I thought it wise to consult an expert—a Super Smarty Plants—Andrea DeLong-Amaya, chief horticulturalist at the Wildflower Center.   Here is what Andrea says:

"It will depend on what species of St. John’s Wort he is growing, but four emitters on a 7 foot dripline will not provide adequate coverage for a shrub the size of the most commonly planted Hypericum sp. in our area (with a spread of 3-4 ft.). I would suggest he get closer to the dripline. Four emitters per plant should be adequate if they are closer."

So, it looks as if you will have to do a little work and move those emitters closer to the plant and to each other to minimize the areas that don't receive water.

 

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