Water is the greenhouse grower’s “Story of Goldilocks and the Three Bears.” Too little water stunts plant growth and yield; too much causes disease or fungus, which threatens a crop’s viability. But, just the right amount of water nurtures a healthy, vigorous crop.

Delivering just the right amount of water is about precision. Typically growers use hand watering, sprinklers, booms, subirrigation and drip irrigation methods.

Hand watering is considered the most inefficient because it is labor intensive and less accurate. Watering systems operated by a central control that can be programmed are relatively inexpensive. Usually, the initial cost of installation far outweighs the expense of crop loss attributed to poor watering.

Sprinklers, booms and subirrigation methods are viable alternatives for some growers, but this article will specifically explore the benefits of drip irrigation.

What is drip irrigation?

Drip irrigation, sometimes called trickle or macro-irrigation, is a low-pressure, low-volume system that delivers water at a gradual rate directly to a specific location. It uses a combination of tubing, pressure regulators, filters and emitters to direct water to an exact location. In outdoor growing operations, the system is installed below the surface or directly on the soil surface. In greenhouses it can be installed overhead with a series of tubes that dangle down into the pot or planting area.

Drip irrigation systems allow for uniform watering application.

“Drip irrigation offers better control of where water is placed in the pot and the amount of water that is delivered to each individual plant,” said Samuel S. Thayer, president of Maxijet. “The result is less waterborne disease and fewer fungus problems associated from watering from above and having too much moisture on the leaves.”

It’s estimated that irrigation systems with sprinklers are 75 percent to 80 percent efficient, whereas drip systems are 90 percent or more efficient at providing water to exactly where it is needed. A drip system highly reduces water loss from evaporation and runoff.

One of the highly publicized benefits of drip irrigation is that it uses less water. Although true in many applications, it’s not always the case. Even in situations where the same amount of water is used, it is being used more efficiently.

“The same amount of water may be used to irrigate, but with drip, more of the water is being used by the plant,” said Nick Webb, of Clearwater Supply, Inc.

In addition to delivering specific amounts of water to the plant, a drip irrigation system can also be used to apply fertilizer and nutrients.

“Drip irrigation systems can be used to fertigate plants,” Thayer said.

Fertigation is the process of supplying fertilizer to a plant through an irrigation system. Because drip irrigation is designed to apply specific amounts of water to an exact location, using the same system to apply fertilizers provides optimum control of fertilizers and or other chemicals to prevent overuse and over- or under-application.

Webb cautioned that drip irrigation is not as easy as “setting and forgetting” a system to operate. “It requires highly skilled management to perform effectively,” he said.

Planning for drip

greenhouse watering

Installing any type of automated watering system can be a significant investment for any greenhouse operation. Before choosing a system or a system design, it’s critical to consider several key elements.

Visualize the greenhouse: Evaluate potential obstacles such as curtains or hanging baskets. Think about where aisles are located in relationship to where the drippers or emitters will be located. Review best practices for the crop you are growing as it relates to the amount of water and water placement preference of the plant. This will determine the height at which the system is installed.

“Greenhouse production is intensive and every aspect of production needs to be looked at,” said Webb. “That includes the inter-relationships between air temperature(s), humidity, airflow, irrigation water source, potential diseases, fertility, harvest, worker efficiency and safety, etc.”

Consider the water source: Whether that is from a municipal water source, the farm’s well or another on-site source, it’s important to know how much water is available and the quality of the water.

“A well or hard water source would need to be looked at closely and an acid injection may be needed,” Webb said.

Regardless of the water source, Thayer and Webb stress the need for a filtration system. “A good filtration system is a must,” Thayer said.

A good filtration system combats a common misperception that drip systems are hard to maintain due to their small orifice sizes. “This can be avoided by using the correct filtration system so that the screen is cleaned often. If the water contains iron or algae the grower can inject certain line cleaners that are safe for plants,” he added.

Webb added, “Filter heavily, and treat the irrigation water to keep clean of biological contamination and to keep the lines clean.”

Identify an electrical source: An electrical source is needed to run a timer that operates the valves and offers zone control. “In an ideal scenario, a drip system should be designed to include a timer that maintains an operating system at 25 PSI water (filtered), about 0.4 to 0.6 gallons per day per square foot if water is available 24 hours/day,” Webb said.

Pressure regulators to keep pressure under 25 and preferably around 15 psi and a variety of different design configurations are available.

Choose a design: “There are single drippers that can go into each pot or there are spider types that one dripper feeds a small feeder tubing into several pots, pressure compensated and non-compensated drippers, etc.,” Thayer said. “The specific design depends on the preference of the grower and the greenhouse needs.”

“Ultimately, the design depends on container size or bed configuration of the crop being grown. Drip can be easily adapted,” Webb added.

Get started

If you think drip irrigation may be a good fit for your greenhouse, consult with a qualified irrigation designer that has previous experience in drip irrigation systems for greenhouse operations.

“You can also contact your local county extension agent and or an irrigation wholesale supply company. Both can provide information about drip irrigation and can offer referrals for experienced designers,” Thayer said.

Avoid cutting corners and create a realistic budget. “Design carefully, don’t take shortcuts and budget accordingly,” Webb added.