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26 November, 2007

Drip Irrigation Lecture Notes for 26 November, 2007


Drip irrigation was brainchild of farmers in the 1960’s – primarily Israeli farmers – needing to water their crops sufficiently and yet conserve water. Drip made it’s way into landscaping in the 1980’s and has continued to improve.

Drip irrigation saves water (and therefore money) in several different ways. The cost of a drip system is so much lower than conventional irrigation that one can install several successive bad drip systems and start over for less money than one bad in ground system.

Drip puts water close to the base of the plant and away from undesirable plants.

Traditional watering methods deliver water faster than most soils can absorb.

Anther advantage of drip is that you can deliver precisely predetermined amounts of water to plants over a wide area.


Minimizes water lost to evaporation before getting to plant Plastic parts wear out or come apart
Minimizes water lost to wind Doesn’t wash out salt build up
Water is directed towards desirable plants and away from undesirable plants Bad for golf courses
Excellent for pots! Many noodgey little parts that get damaged or lost
Easy to install and adapt Not efficient for established trees
No trenching! Tubing is exposed!
Can be easily used with other systems Rodent/human damage
First evidence of a system problems is usually a dead or dying plant

Another advantage of using a low flow drip system is that you do not need high pressure to supply the drippers and micro-sprinklers. Most drip systems run about 15 to 30 PSI (pounds per square inch). For comparison most houses have water pressure of anywhere from 40 PSI to 60 PSI. The benefit is that you do not have to worry about large pressure drops in your household water flow just because the irrigation system has turned on; for example you will not notice if the system goes on when you are in the shower!
Starting To Drip

How you will connect to your water source depends on several factors:
1. How large of a system will be needed?
2. Your expertise and desires
3. Water quality and pressure
4. Site requirements

Types of connections:
1. Simply screwed onto the end of a hose bib (use a Y connector)
2. Tee’d off the water supply

Valve type:
1. By hand
2. Inline controller, usually battery powered
3. Multi-station controller wired to valves

Pipe wrenches
Hack saw
Emitter punch
Electric drill
Masonry bits
Screw drivers
Several pliers

Emitters (aka drippers)
Poly tubing – ½” and ¼”
Anti-siphon device
Pressure regulator
A million adapters & noodgey parts
WD 40
Plumbers tape

Designing Your System

Rule 1: You cannot exceed your water supply!
If you only have 100 gallons per hour (GPH) of water supply (example only) then you cannot make one system/watering zone that uses 200 gallons per hour (GPH). Just common sense! What we can do in this case is to make more than one watering zone from the same water source – divide and water.
Rule 2: You must have some water pressure, but not too much!
Most homes have between 40 to 60 PSI (Pounds per Square Inch). This is just fine for a drip system, in fact it is more than you want but this is good! On a drip system we always want to have the pressure between 20 to 30 PSI. For this we have preset pressure regulators.

Rule 3: Only a certain amount of water can flow through a given size pipe at a set pressure!
This one sounds serious but it is simple and one of the numbers/rules to memorize. As an example, our .700 size polytube at 25 PSI can have only 220 gallons per hour (GPH) flow through it. So even if your water source can supply more the polytube cannot support it. This means that if you have a preset pressure regulator (which is 25 PSI) you can only have a maximum flow rate of 220 GPH from each polytube. This is important because all the water outlets (drippers & microsprinklers) cannot exceed this maximum flow of 220 GPH. All of our products have flow rates listed so it is easy to add up the total water usage from each emitter and microsprinkler.

Rule 4: You cannot go an unlimited distance on a single polytube!
Even if you have a single dripper at the end of a line you cannot run any distance you want. This is where the laws of physics get in the way again! For every "X" amount of feet you run the polytube (or any pipe) you will loose a certain amount of pressure due to "Friction Loss" (don't ask about friction loss only engineers need to know this stuff!). So anyway you have to obey the maximum line lengths allowed, these are listed for almost all the drippers and microsprinklers we sell.

To plan your system correctly you will need to find out your available water supply (how many gallons per hour your system produces).
To do this, follow these steps.
Turn on the water supply all the way
Place a 5 gallon bucket in the water flow for set amount of time. We will use 30 seconds as an example.
At the end of 30 seconds take the bucket out of the water flow.
Turn off the water supply. (we know, but..........we gotta say this!)
Check the bucket and estimate the amount of water in it. Or measure it with a gallon milk jug.
We will use an example: Let's say 1/2 of the bucket is full, remembering that our bucket holds 5 gallons......1/2 full must be close to 2.5 gallons. Take the amount of water in the bucket and multiply it out so you will know how much it would have been if you left the bucket under the water flow for a full minute. In our example we have 2.5 gallons in 30 seconds, or half a minute. Because we want the number of gallons per minute we use the calculation 2.5x2 = 5 gallons. If we had gotten 2.5 gallons of water in 15 seconds then we would have done 2.5 gallons x 4, because 15 seconds is ¼ of a minute.

Take your answer from step 6 (above) and multiply it by 60. Our example would be 5 x 60 = 300. The 60 is for 60 minutes because we want to find the Gallons per Hour (GPH) total water available. In our example we have 300 gallons per hour (GPH) available for our system.

Take an overall look at the area to be watered. If the area slopes, one must consider how steeply it slopes and in which direction. Elevation change is another factor that leads to pressure variations. If the tubing runs downhill, pressure increases by .433 psi per vertical foot. An equal amount of pressure is lost when the system runs uphill. If the difference between high and low points of the system is no more than 25 vertical feet and pressure-compensating emitters are used, then the pressure variation is acceptable. On a hilly site with greater elevation changes, the main problem is that the pressure starts to strain the tubing and fittings. Our solution is to start with a 20 psi pressure regulator at the top of the slope, and install an extra 20 psi pressure regulator every 25 feet down. Decide whether each area is best watered with drippers or microsprays.

Factors to Consider Between Drippers and Micro-sprays
Can be completely hidden by mulch, protected from sun and human damage Cannot be completely hidden, vulnerable to disturbance by children, pets and other critters
Need a larger number to water annual beds or ground covers Can be placed 5 to 8’ apart ameliorating tubing use; easier to cultivate around
Precise placement of water Not as precise, poor choice for decks; wider wet area increases weed growth
Minimum water loss by evaporation 20-30% water loss due to evaporation
In a typical landscape, the water use by plants in a drip system improves as the plants mature. Roots growing deeper increase the depth at which water may be utilized by plants Coverage from spays deteriorates as plants grow and block spray pattern
Maintenance of a drip system requires careful attention and inspection Misters obviously are working or they are not

If you are contemplating watering your whole landscape, or collections of plants with wildly varying needs, with drip – and it’s an extensive project – you will need to divide your project into different zones, each one controlled by its own valve. This still doesn’t elevate installing a drip system to rocket science mode.
Design Considerations

Water moves downwards in soil due to gravity and from particle to particle in all directions due to capillary action. In coarse sandy soil, gravity affects water movement more than capillary action. In finer soils such as clay, capillary action is much stronger, so water will tend to spread before penetrating very deep. An emitter in sandy soil may suffice for an area 16" in diameter, while the same emitter in clay soil may wet an area 24" or more in diameter. A field test is useful: slowly drip water from a garden hose on the soil to be irrigated; after half an hour, check to see how deep and wide the water has spread. Be sure to dig down into the soil away from the obvious wet area on the surface to see the extent of coverage.

Drip emitters are typically available in flow rates of 1/2, 1, or 2 gallons per hour. Factors that influence the choice of flow rate include:
(1) different rates are used to give different amounts of water to plants on the same system;
(2) sandy soil takes a fast drip rate, while a 2 gph dripper in clay soil produces a puddle of water and may result in dirty water getting back into the drip tubing;
(3) choosing slower drippers allows you to use more in a single zone, and allows longer runs of tubing.


As lines are laid out, the tubing may have to be secured until it takes shape. This can be done with stakes designed for this purpose. Leaving a little slack in the lines will allow for expansion and contraction from temperature changes, and will help prevent emitters from moving out of position.

Emitters- Once the lines are in place and flushed, the emitters can be installed. Simply make a hole in the tubing with a hole punch, then pop the barbed end of the emitter into the hole. If you punch a hole in the wrong place, it can be fixed with a goof plug.

There are four ways to install emitters. The most common method is to place the emitter directly on the line. This way you only have to punch the hole and pop in the emitter. Another way is to install a connector into the line, run 1/4" tubing to the place where the water is desired, and push the emitter into the end of the tubing. A third way is to place the emitter on the tubing and use 1/8" or 1/4" tubing to transport the water to the base of each plant. Finally, you can cut 1/4" tubing and insert an in-line emitter that drips and also allows water to pass through to the next emitter.

To install a spray, first punch a hole in the main line and insert a 1/4" connector. A short length of 1/4" tubing then leads from the connector to a stake. The spray screws directly into the stake and can be raised with an extender if it is blocked by plants. Some misters are supplied already attached to a spike which pushes into the soil, and a barb to which you attach 1/4" tubing to supply water. Others are designed to be attached directly to tubing above the plants—in a greenhouse or above a hanging basket, for example.
Drip in Containers

All but the smallest containers need several emitters placed in them because soil is so much more loose than garden soil that water from each emitter moves downward without enough sideways spread. The irrigation strategy is to place drip emitters 6" apart, or to attach small adjustable bubblers to spread the water. Useful products include mini-inline emitters, 1/4" emitter lines, shrubblers, and vortex sprays.
If a new installation, tubing can be run up through the drain hole (and out of sight).

Adjusting the number and size of emitters in a container drip system takes some experimenting, especially if the containers are of different sizes. Run the system and see which containers the water runs out of first. You either have to decrease the flow in these or increase the flow rate to the other containers on the system. This process will also help you set the run time for the system.

Dripping Vegetables

While veggies want baseline of moisture in their root zone, frequent overhead watering encourages rust, mildew, blossom damage in more than a few species and these weaken plants leading to the possibility of disease.

Depending on your personal needs and likes, vegetables can be watered using in-line drippers – either in ¼” or ½” poly tubing – or by using soaker hose. If plants are more widely spaced and deeply rooted (for example, tomatoes and squash), plain poly tubing can be utilized with a single emitter placed at the base of each plant. Root crops such as carrots, onions, and radishes can be planted two deep on each side of a single emitter line. With plants such as corn, strawberries, and peppers, one row on each side is preferable.

You want a simple system that is flexible and can be easily moved for cultivation and replanting.

Ornamental Beds

Drip can really shine in the ornamental border. Established shrubs can have their own more or less permanent drip line and emitters, while smaller plants, or areas given over completely to annuals can be watered using small sprays or emitters on a ¼” line that is rerouted as needs change.

Times and intervals for watering different plants are greatly affected by the factors of soil type, root depth, air temperature and humidity, wind and the plant’s maturity. The deeper the roots and the finer the soil, the longer the watering time must be, but you can reduce the frequency of watering because clay will hold the water tenaciously. Shallow root zones and sandy soil types will require frequent waterings of a shorter duration.
The object of each watering is to bring the moisture in the root zone up to a satisfactory level. Once the desired moisture content is reached, no more water should be applied. Too much water cuts off necessary oxygen and washes nutrients out of the reach of the roots. Before the soil has dried out too much the system should be run again. In this way the plants can be maintained in near optimal conditions.

The only way to come up with appropriate times for your garden is through observing plant and soil moisture conditions, asking local experts (agricultural extension agents, nursery personnel), and continuous twiddling with your watering times and intervals to maximize growth and minimize water use.

Some Suggested Watering Times to Start With:
Type of Plant Time (in hours) Intervals (in days)
Low Shrubs (2-3’) 2 3
Shrubs and trees (3-5’) 3 4
Shrubs and trees (5-10’) 4 5
Trees (20’ and over) 5 6
Flower beds 1 2
Ground covers 1 2
Vegetables – close spacing .5-1 2
Vegetables – wide spacing 1.5 2
Potted plants 1-10 mins 1

Selection, Number and Spacing of Emitters
Flow Rate (GPH) Number of Emitters Placement of Emitters
Low shrubs (2-3’) 1.0 1-2 At plant
Shrubs and trees (3-5’) 1.0 2 1-12” either side
Shrubs and trees (5-10’) 2.0 2-3 2’ from trunk
Shrubs and trees (10-20’) 2.0 3-4 3’ apart
Trees (over 20’) 2.0 6 or more 4’ apart
Flower beds 1.0 1 At plant
Groundcover 1.0 1 At plant
Vegetables, closely spaced 0.5-1.0 1 Every 12”
Vegetables, widely spaced 1.0-2.0 One per plant At plant


Occasional maintenance should be carried out on all drip irrigation systems. Inspect the flow from each emitter, flush lines by unscrewing the end caps and turning the water on, and clean the filter. The development of drip irrigation products now in their third decade has led to successful and trouble-free systems for both the farmer and the homeowner. The design of a system using filtration and quality emitters will make maintenance a simple quarterly task. Visual inspection of the system is the best way to observe performance, and can be done in minutes while gardening.

Plan a complete inspection of your system at the beginning of each season. This may be all that you need to do unless there is much foot traffic or animal damage. The other time to check your system carefully is after any new planting or garden maintenance that may have damaged the tubing. If you are having trouble with your system, conduct the standard maintenance procedures first. If the problem is a single emitter, replace it. If it is more widespread, look for a break in the lines. If the problem cannot be determined by observation, it may be a result of inadequate water supply or faulty system design.

Goof plugs can be used to plug holes from which emitters have been removed. They are very simple to use, and are indispensable when doing repair work or changing your pattern of plantings. Likewise, couplings come in very handy when any repair needs to be done on a damaged section of line. Simply cut out the damaged section and install a new piece using the couplings to connect the two pieces together. Goof plugs and couplings should be ordered with all systems. If they are not needed in the initial installation, they will form the backbone of your repair kit.

(Note: the actual handouts that follow should have illustrations and figures in them, but I can't figure how to get them out of Word into the blog. If you feel you need them, email me and I'll shoot you originals. david)


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