The Best Drip Irrigation Systems: How to Choose an Irrigation System for Your Farm, Garden or Greenhouse

Are you considering adding a drip irrigation system to your operation? Drip irrigation is one of the best options for the home grower and market gardener alike. Anyone wanting to conserve water, reduce weeding, and deliver even watering to their flower and vegetable crops for optimum growth should install some form of drip irrigation.

Read more below to learn what drip irrigation is, what factors to consider when planning an irrigated space, and how to purchase the right kit for your growing space. For more information on some of the commonly used irrigation terms, we have included a glossary of terms at the end of this article.

What is Drip Irrigation?

Drip irrigation is a crop or landscape irrigation system designed to make watering simple and often automatic. Basic systems consist of a supply line, filter, and pressure regulator feeding drip tape, tubes or single emitters in order to distribute a specific amount of water to a precise location in a predetermined amount of time. The best irrigation systems also include timers and sensors for automatic shut off and local weather conditions. 

Benefits of Drip Irrigation

Water conservation, efficient wetting of the root zone, and plant-level application are among the most touted benefits of drip irrigation. There are benefits well beyond those as well. 

• Low Water Consumption. 

Drip irrigation conserves water by eliminating the risk of wind drift, evaporation and runoff. When we use inaccurate overhead sprinklers, we throw water to the wind, with some evaporating before it even makes contact with the soil.

• Efficient Water Distribution. 

A percentage of the water from overhead sprinklers that makes it to the soil will be between rows and some outside of the garden. Drip irrigation efficiency ensures that the water only goes where you want it to. 

• Easy System Setup and Maintenance. 

Good irrigation systems come with instructions and the set up is a series of repeated steps that are easy to master. Maintaining the system requires only occasional repairs and end of season flushing. 

• Ability to Water Plants at an Individual Level. 

Kits for smaller gardens can be outfitted with individual emitters specific to a plant's needs. 

• Reduced Weeding Efforts. 

The targeted application from drip irrigation prevents water from missing the target crop’s rootzone and inadvertently germinating weed seeds between rows. 

• Increased Plant Growth and Health. 

Limiting wetting leaf and stem tissue helps to control fungal diseases that can severely damage plants.

• Reduced Plant Stress. 

Drip irrigation puts the water precisely at the plant's root zone giving them consistent access to water and significantly reducing stress. 

• Help Reduce Soil Erosion. 

Runoff from drip systems is minimal due to the precise and slow application. Sprinklers can cause excessive runoff and pooling of water that leaches the soil and washes it away. 

Understanding Drip Irrigation Basics

Filtration for drip irrigation systems.

The most important part of any drip irrigation system is the filtration. Without a good filter your system risks clogging which results in uneven application. The small orifices in drip irrigation have gained in leaps and bounds with designing clog free emitters, but we want that as a fail safe in the event the system is infiltrated by contaminants.

Your drip tubing, tape or emitters are going to call for a filter to meet their specifications, following their recommendation will yield the best results. As long as you do not put too much pressure into it, and you drain, and store your filter out of the sun when not in use, it should last you for years.

There are many types of filters and I have tried quite a few styles and brands. Although they are quite simple, you do get what you pay for and the filter protects the entirety of your drip system. If you think chasing leaks and patching holes is frustrating, the irony of having a drip system that doesn't leak but also doesn't drip may push you over the edge. Which brings us to our next topic…

Water Hardness in Drip Irrigation Systems

Water hardness, as I have found over the years, is an incredibly interesting topic. There are a lot of factors at play. We will not be diving into that here, but we will discuss “hard water” which falls into a fairly wide range of PPM, EC or GPG (essentially different ways of measuring the dissolved solids in water). 

When I lived in Montana 150 PPM well water was considered hard, in South Dakota well water frequently tests at 1000+PPM! Clearly hardness issues may be more severe when irrigating with “hard water” Montana vs hard water in South Dakota.

The central issue that hard water creates is a build up of mineral deposits. You may see this as a white crusty build up around faucets and hose bibs on your property. This build up can clog emitters.

Water Softeners use salts to remove water hardness. The process replaces the hardness with salt, DO NOT USE softened water for irrigation water! Your soil will be destroyed over time. There is a reason that salting the earth was a tactic of war in ancient times. 

To use drip irrigation with hard water you may need to flush the system periodically with an acid solution, acid injection is also an option. Fertigation equipment can be used to do this acid injection. Treating hard water is going to be an added expense and it is best to look into your water hardness before installing the system.

Understanding Basic Irrigation Terms 

GPH, GPM and PSI. OH MY!

In irrigation setup instructions of any kind you are going to see a lot of abbreviations and there will be some required math. This will be very basic and we are going to touch on some things YOU can do to ensure you size your irrigation properly.

Why do GPH, GPM, and PSI matter when choosing a system?

Finding our actual water source GPM or Gallons Per Minute takes less than a minute. The only tools you will need are a bucket and a stopwatch. The reason to perform this simple test is to make sure we know our actual water supply flow rate. 

For example, you may have a 50 GPM well or an entire municipal water supply available, but your limitation in nearly every case is going to be your supply hose/pipe Inner Diameter(I.D.).

The limit for water flowing through a standard ¾” hose is based on the supply pressure. We will more than likely see somewhere in the 10-20 GPM range coming out of the supply line. Our GPM is affected by tube diameter because of the amount of friction of the water on the walls of the tubing. 

A larger tube/pipe/hose will reduce friction and improve flow, there will always be a certain amount of drag so you will not be able to meet the full capability of the water supply. 

I always say to build a drip system with the largest tubing the budget and irrigated crop will allow. I have yet to over engineer an irrigation system and regret the increase in material cost.

How to Calculate Gallons Per Minute (GPM):

Tools needed: 5 Gal. Bucket, Stop Watch

1. Place your 5 gallon bucket beneath the water supply 
2. Turn the water on and start the stopwatch at the same time.
3. Run the water for 15 seconds 
4. Shutoff the water and measure what you have in the bucket
5. Multiply the amount of gallons by 4 (15 x 4 = 60 seconds= one minute) That’s it, you found your GPM of your water source!

GPH are Gallons Per Hour so it is simply  GPM x 60 = GPH. GPH is generally used for drip irrigation emitters, these systems slowly drip water so the run times for an irrigation event is measured in hours. 

If you are using a drip tape or drip tubing the manufacturer has set the emitters at a specified spacing, and those emitters are going to distribute water at a set rate determined by the PSI of the water supply. The emitter MUST be supplied AT LEAST the amount of water that the emitter is rated to flow or your irrigation pattern will be very erratic if a pattern at all. 

For example,  a drip tubing with 1 GPH emitters spaced at 12” and measuring 100’ long will require 1.67GPM. Because 1(GPH) x 100 (number of emitters when spaced at 12” in a 100’ run) = 100 GPH

100GPH/60 (minutes per hour) = 1.67 Gallons Per Minute.

This example shows just how simple the design can be for a drip system using tubing or tape, but what about individual emitters? Sometimes we want to irrigate landscape plants that may be perennial or we are looking to get containers, hanging baskets or other irregular shaped plantings. This is where individual emitters shine. 

Individual emitters are easy to use and generally can be fed by a small and hideable 1/4 “ tubing. You will simply need to add up the GPH rating on each emitter on a zone (emitters that will run during the same irrigation event) and make sure they can all run on the same PSI (the GPH rating can be mixed sizes in these systems as long as the sum of the emitters GPH does not exceed the supply GPH).

Checking the PSI of a Water Source

The PSI is the pounds per square inch of pressure. This can be checked on a gauge at the pressure tank of your system if you have a well, if you are on a municipal water supply you are going to fall between 45 and 85 PSI generally speaking. The good news with drip irrigation is it is generally a low PSI system with the highest PSI rating of drip tubing, tape or emitters being somewhere around 45 PSI (averaging 10-20 PSI). 

How to Regulate Water Pressure for Drip Irrigation

It is important to meet PSI requirements for your specific drip irrigation kit. This often requires the use of a pressure regulator to increase or decrease  the flow rate. The regulator also helps the system to maintain an even pressure  by preventing dips and spikes that would create uneven flow through the system. 

You will notice drip emitters, drip tape and drip tubing are rated at different flow rates based on the PSI in your system. Your regulator is an integral part of your system. Sometimes a regulator change can reduce or increase irrigation volume enough to avoid changing drip tubing or drip tape, which can be costly for larger plantings.

Reading Wetted Patterns 

Overhead irrigation did come with the perk where we could visually see the wetted pattern. If our plants are in the wetted pattern they will survive.  We do tend to notice different amounts of coverage and this is based on the way the sprinkler disturbed the water droplets as they are thrown from the sprinkler head. 

There are many designs aside from the impact but they all are similar in that none of them are perfectly uniform. This is fine when we have an abundant water source or our irrigation events are few and far between. When regular irrigation is needed or irrigation water is limited and/or needs to be accounted for by volume, our water placement gets a lot more critical.

With drip irrigation however, the wetted pattern is a bit more tricky to see as most of it is under the soil surface. Drip emitters let a precise amount of water through a small orifice at a determined flow rate. These flow rates are generally in GPH or Gallons Per Hour. As the water is slowly applied to the soil it leaves a small wet spot and tends to drain in a teardrop pattern in loamy soil.

In a sandy soil the wetted pattern is more narrow and elongated because the water is draining more quickly preventing it from spreading horizontally. In the same way the denser our soil (smaller the particles) the more resistance the water will meet trying to drain through smaller gaps in the soil particles. 

This is no problem, in denser soils we use a lower GPH emitter to keep our wetted pattern a tighter diameter and in sandy soils we can use a higher GPH emitter for an increased diameter wetted pattern. Unsure about your soil composition? Check out this article on determining the texture of your soil.

Pressure Compensation in Drip Irrigation 

Drip irrigation wetted pattern also includes our overall distribution of our system, whether that is multiple emitters at larger high value crops or single emitters embedded in a drip tape or tube along a row of lettuce we want all of our emitters doing the same thing, EVENLY distributing a predetermined amount of water over a specific period of time. 

We had discussed our supply PSI and GPM earlier but we can also have distribution problems from uneven ground. This tends to be more of an issue in longer runs when we are putting the flow rating of our drip tape or tubing to the test. 

This can also be an issue when using individual emitters to water baskets or pots that may be at differing heights around the greenhouse or patio. The solution is using a drip tape, tubing or individual drippers with pressure compensating emitters. 

While our pressure and flow does need to fall within the specification of the pressure compensating emitters, the pressure compensation will make up for undulations in the field and compensate for supply surges to keep our emitters distributing our irrigation water as efficiently as possible.

While most drip tape and tubing is used on the surface the vast majority of the time, subsurface drip irrigation has gained popularity over the years. These drip tapes tend to be much thicker and much more rigid or are a drip tube. 

The thickness is to prevent rocks or abrasive soils from rubbing a hole in during install or expansion and contraction (while buried tape and tube expand and contract less, they will still contract to some extent when cool water flows through them.) 

No Clog Emitters in Drip Tubing or Tape

Drip tubing or tape will have built-in or individual emitters with both inlet and outlet openings. The inlet emitters will often have some form of a filter, trap, or maze for the water to pass through that will, in turn, catch any particles not trapped by the water source filter trying to make their way in to clog the emitter.

After all, installing the system is most of the work. The longer you can simply maintain and utilize a drip system, the more value you are going to get out of the system because, per x hours of installation, you get multiple seasons vs. one.

Is Drip Irrigation Worth It?

Drip Irrigation in its efficiency tends to feel too easy. After the installation we do not need to lug the hose around the garden, careful not to crush our delicate vegetables. No more worrying about pulling lettuce up with the hose as we hand water our tomatoes. Simply turn on the hose ( or set up an electronic timer to water your plants automatically) you can even work in the garden during an irrigation cycle. To me that is worth it.

In fact, as you work the garden the only evidence your plants are getting their hydration will be a random gurgle or a wet spot underneath your emitters. All the work is really in the planning and installation. The biggest issue is that it's easy to overwater with such a convenient system if your system is not set up with a timer.

Complete Drip Irrigation Systems

Now that we understand the concepts behind drip irrigation and we have looked at what it takes to get ourselves ready to design a drip system, it may be worth looking at a kit ready for installation into a garden or hoop house. There are as many drip kits available online as there are vegetable varieties. All of the kits you find are going to accomplish the same goal, what sets them apart is the quality of components, complexity of design, and the intended life of the system. 

As with everything in the garden, there is a give and a take. If you go for the savings you are probably going to find yourself repairing and patching your system a lot more frequently. I have gone this route, and knowing the compromise I was making helped me to get through a summer of 8 mil drip tape. 

It was bearable only because I had ordered a lot of patches in anticipation of the rips and holes and I also ordered extra tape. This was a one acre strawberry planting so I was already intending to spend a lot of time out there during the irrigating season. After that first season of chasing leaks, that tape was upgraded with a more permanent drip tubing irrigation kit intended to last through an entire berry planting of several years.

A pre-designed kit like the one linked above is also going to include a filter specific to the emitters embedded in the drip tubing or tape. This filtration is imperative. With the small orifices drip emitters are at risk of being clogged by particles that may be in your water supply. 

Along with the filter you will want to make sure the kit has a backflow preventer to ensure no water makes it back into your water supply potentially causing contamination. A good kit will also include a pressure regulator to ensure you get the best uniformity out of the system.

Complete Irrigation for Gardens

For smaller plots and raised beds there are additional fittings that you will need. This raised bed watering kit has elbows, tees and 1⁄4 inch emitter lines that allow you to customize drip irrigation for tightly planted beds. 

The kit can cover up to 150 square feet and you can easily combine kits to cover 700 square feet of plantings. To simplify your life you can also add a timer to the system that keeps your watering schedule even when you aren’t around to turn it on. 

Glossary of Irrigation Terms

PPM - Parts Per Million

EC - Electrical Conductivity 

GPG - Grains Per Gallon

GPH - Gallons Per Hour

GPM - Gallons Per Minute

PSI - Pounds per square inch of pressure 

Drip Tubing - Tubing with drip emitters embedded at a specified spacing along its length

Drip Tape - Flexible, collapsible tubing that lays flat when not in use with drip emitters embedded at a specified spacing along its length

Supply Line - The hose, pipe, or tube bringing water into the system

Emitters - (drippers) Used to control the flow of water, embedded in tape tubing or individual ¼” barbs for use on ¼” tube

Filter - A screen, sieves, or discs used to trap small particles in supply water

Fertigation - is a method of nutrient application where fertilizers are injected through an irrigation system.

Backflow Preventer - a check valve to ensure no water is allowed to flow back into the supply water

Written by Andy Russo, Russo Tree Farm