Drip Emitters
Selecting the Correct Type
Standardizing each Zone
Garden Tip
Technical Bulletin Series
The first thing in planning or upgrading your irrigation system is making the best selection for which type of "drip emitter" you intend to use. As you will read later in this bulletin, mixing different types of emitters on the same valve or zone will create added problems. So, picking the type that will serve all the plants on any single zone is very important.

Larger shrubs and trees require a greater number of emitters with these being well distributed throughout the Rootzone. In order to establish a root system with enough capacity to nourish whatever sized plant the spacing MUST take into consideration the composition of the soil. When the soil is sandy (and drains well) the emitters need to be closer. When the soil is high-clay, the emitters are spread out more to allow that slow draining soil to absorb the water. Placing too few emitters will cripple root development.

Using a large quantity of single-independent emitters can create a complex installation, and with each emitter comes the added opportunity to trip on it when walking in the area. This I believe is why spraying-adjustable Shrubblers are so often selected.

Too often "Shrubblers" like this are selected and used in order to provide an amount of water that would be equal to 10 or so 1 gph single emitters. And they are adjustable.
This type of emitter
it really is NOT drip - it is spray
is frequently the cause of plant
stress and ultimately failure.

Here are some reasons:

    They put out as much as 12 to 15 gph and this water is distributed over an area of only .78 sq ft to 1.2 sq ft. That is 12.5 gallons per sq. ft. per hour. This will puddle and run off if it runs too long. So, typically the run time is set for only 7 minutes. This provides 1.75 gallons of water in a 1.2 sq. ft. area. A 12 foot tree has a watering area of at least 70 sq. ft. That would require 58 of these Shrubblers, and nobody comes anywhere close to doing that. Typical is to install 5 or 6. Too much water in a small area in too little time.

Over time, when soil moisture is severely
limited in its depth and surface area something has got to give!

Roots that look more like this

   Instead of looking like this
More reasons that Shrubblers aren't the right choice for larger shrubs and trees:
    They Adjust! This seems to make them popular, but think about this complications: When adjusting one of them (let's say increasing flow) you reduce flow on all the others to a degree (because you have reduced line pressure). This is like "whack-a-mole". You really do NOT know how much water they are putting out, and because they adjust - they plug more often.

    These Shrubblers are meant to be high-flowrate, but slow application of water permeates deeper and produces deeper root systems. There are 12 excellent hours during the day to run irrigation - why try to do it all in 7 minutes?

    Because each Shrubbler can use so much water so fast - the ¼ inch feeder line can only provide water to two of these devices and much not exceed 20 feet in length (or flow rate will drop).

Here are more options for High-Flow-Rate Devices

High Flow Rate (3 to 15 gph)
¼ inch Shrubbler

High Flow Rate (3 to 20 gph)
¼ inch Bubbler

High Flow Rate (0 to 30 gph)
½ inch Bubbler
Dripperline (with emitters fabricated right into the tubing) offers a simple solution to these issues and is very economical. It comes in ¼ inch and ½ inch diameter. The ¼ inch has options of 6 or 12 inch spacing between emitters. The ½ inch diameter offers 12 and 18 inch spacings. Simply hook one end up to the feeder line and plug the other end. Space the rows appropriate for the size plant. Secure their position if you like and cover them with organic or rock mulch. Each emitter puts out approximately 1 gph.

Dripperline with "inline" emitters

Closeup of a single emitter in a dripperline

Spacing for large shrubs and trees
Typical spiral of dripperline around a tree

By creating a "spiral" of Dripperline around a shrub or tree, and spacing each row by between 6 and 12 inches, you will have created an excellent water and moisture distribution pattern all throughout the rootzone surface area. With the slow rate feed of these emitters, the water soaks deep, and total water use is minimized.
Ideal irrigation distribution
most closely

approximates rainfall!
Dripperline; economical and effective
There are many other options for Slow Flow Emitters
- here are a couple -

Flag Drip Emitter (1 to 4 gph)       PC Drip Emitter (0.5 to 2 gph)
All Emitters on the same zone should have similar flow rates!
A frequent problem I have observe during on-site consultations is "mixed" emitters. Shrubblers or fast flow rate emitters on the same zone with drips (slow flow rate). Emitters that "spray" are not drips. Sprays are intended for proving surface moisture (annual flowers and turf). Drips are intended for deep penetrating moisture, required by shrubs and trees.

If you have these different types mixed together on the same zone, some plants are going to be over-watered while others may be under-watered. If you reduce the flow on a high-rate emitter to match a drip it is likely to perform erratically, due to its operation being at the border of its range.
Whichever type of emitter you select, you really need to stick with that type
throughout any single zone or valve. This is what is meant by
"Standardizing your Emitters"!

Have you taken a stroll through your landscape to inspect your drip irrigation?
You need to check for adequate emitters count and coverage
for each plant as well as for plugged emitters.
Advantage of Slow Rate drips: These are often pressure compensated "PC". This means if you decide to add a few extra to the line (more plants) the flow rate (for each) will remain constant. The water for the new plants will not be at the expense of the established plants. Whereas the limit for high rate Shrubblers on one zone is typically 25 (if fully opened), it is practical to have as many as 200 slow rate drips on the same zone without complications. Slow flow rate drips will allow much deeper penetration of water, giving you plants with deeper roots. Deep root systems mean healthier more drought tolerant plants.

The best watering for shrubs and trees is slow and deep. Expanding the watering zone as the plants mature and routinely inspecting for trouble. Set your clock to 45 minutes or more with slow rate drips, and avoid frequent every day scheduling, even in the heat of summer! With deep roots, plants won't wither in a single day, and the time off allows them to breathe.

If you do happen to have your trees or shrubs on the same zone as your lawn, this creates a situation with a very complex solution. I recommend that you contact a "Soil and Irrigation Specialist" and ask for advice specific for that situation. A good answer would be too long and complicated for a written article like this.