Q. The landscape people
are into variable drip emitters and think I am a little looney sticking to drip
emitters. How do you determine how many
gallons to give large trees like African sumac, bottle trees, Swan Hill
olives, Yew pines and chaste trees?
A. No one puts it in gallons because there are too many
different manufacturers and rates of deliveries of different irrigation
emitters and sprinklers. These can vary from 1/4 gallon per hour (1 liter) to
five gallons per hour. Then there are the types that are variable and can be
twisted open to give you more or fewer gallons per hour.
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| Drip emitters color coded for gallonage |
You have to figure
make the conversion and convert it yourself. It is not terribly hard to do,
particularly in drip irrigation. Each emitter is labeled or color coded to the
gallons per hour that they emit.
The hardest emitters to figure out are the types that can be
adjusted (variable) to different amounts of water. Many of these are adjustable between 0
(shut off) to 10 gallons per hou
It seems simple. You just twist the emitter
open and it delivers more gallons per hour. But in actuality it begins to
defeat the purpose of drip emitters: precision. Also many of these variable
flow emitters are not pressure compensated. If it is not pressure compensated,
then opening one emitter and allowing more gallons to flow can affect the number
of gallons on all the other non pressure compensated emitters on the same line.
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| Variable drip emitter |
This can mean you have to twist open or twist close each emitter along the same
line perhaps multiple times to get the flow that seems to be appropriate. Not
only that but these variable output emitters frequently emit so much water so
quickly at the higher settings that it results in water puddling and running
off to low spots. This is exactly contrary to the reason we should use drip
emitters.
With many different types and sizes of plants along the same
line the next difficulty for most people is to figure out what size (gallons
per hour) to match up with each plant along the line. So this is how I do that.
The first thing I do with an emitter line attached to a single valve is
determine how many hours or minutes the valve will be left open for watering.
Frequently for drip irrigation the shortest time is one hour.
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| Flag emitters easy to clean and color coded |
“Yikes”
you might say because most people want to irrigate fifteen or twenty minutes.
The problem with these short irrigation times is that it may force you to use
the variable output emitters. Or it results in water applied so rapidly it does
not penetrate the ground and instead runs and puddles somewhere else.
Start
with a minimum of one hour. In some cases you might water for two or three
hours on a single line. What difference does it make? You are not standing
there with a hose and it can take all night if you want it to. There is no
problem watering at night with drip irrigation. Let it soak long, slowly and
deeply.
Try to use at least two emitters per plant in case one plugs. Here is
the one hour example. One gallon plants, give them one gallon per hour (two,
half gallon per hour emitters). Five gallon plants give them three to five
gallons per hour (two, two gallon per hour emitters or three, one gallon per
hour emitters). Fifteen gallon plants give them 8 to 15 gallons per hour (two,
four gallon per hour emitters or two, five gallon per hour emitters or three,
three gallon per hour emitters, etc.)
Distribute the emitters under the plant
canopy, one foot from the plant with distribution tubing and secure them in
place with rock mulch or stakes to hold them in place. Emitters should be above
the mulch so you can check them for plugging. Plants that are spaced closely
together can and will get water from each other.