Tailor emitter flow rates too

While most expert sources recommend extra emitters on thirstier plants, many claim a system’s emitters must all have the same flow rate. In fact, as I discovered last year, tailoring emitter number AND flow rate is a conservation and horticulture win-win.

Plants, exposure, and soil vary markedly within residential irrigation zones. As WUCOLS III (Water Use Classification of Landscape Species) allows, “Collections of species are commonly irrigated within a single irrigation zone, and the different species within the irrigation zone may have widely different water needs.” WUCOLS IV details 3,500 plants in 6 California regions, yet does not weigh in on how to handle variations.

Our 2012 professionally-installed system used all 2 gallon per hour (gph) emitters, with two on each tree and one on each shrub, succulent, and groundcover. Hypothesizing that mixed flow rates would help my 2014 sustainability quest, I experimented on one zone to align flow rates to plant needs and cut run times. After water use plummeted and plant health improved, I extended the breakthrough process to all zones.

Now, blue 0.5 gph, black 1 gph, or red 2 gph emitters match plants’ stated water use, sun/shade exposure, soil type, and slope. Two smaller emitters rather than 1 bigger one spread roots beyond a single drip, unless only 0.5 gph is needed. These mixed flow rates made 25-60% run time cuts viable, optimizing consumption. Plants got no more or less water than needed, in more than one small spot, optimizing vitality.

Data below illustrates one zone’s before and after.

BEFORE Plant Example AFTER
# Emitters Emitter gph Gallons in 45 Minute Run # Emitters Emitter gph Gallons in 30 Minute Run
1 2.0 1.5 Scaeveola ‘Mini’ 1 0.5 0.25
1 2.0 1.5 Rosmarinus 2 0.5 0.5
1 2.0 1.5 Agave ‘Blue Glow’ 2 1.0 1
1 2.0 1.5 Loropetalum 2 2.0 2
2 2.0 3 Arbutus ‘Marina’ 3 2.0 3

Perhaps experts advise against different flow rates on a system because they consider mixing to be complicated or unnecessary. This 15-month case study proves that direction is unwise.

One size does NOT fit all in sustainable gardens.


Definitions:

  • Emitters, disperse water dripped at a controlled rate from drip lines to plant material. A great range of design types exist, with flow rates from 0.5, 1, 2, 4, and even more gallons per hour.
  • GPH is gallons per hour.
  • Zones are groups of plant material irrigated at the same time.

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