Trade Your Greenhouse Labor For An Automated Irrigation System

Because plant production has become an increasingly competitive business, efficiencies in all aspects of greenhouse and nursery management are now more important than ever to maintain profitability.

With the stepped-up pressure to increase productivity, while still generating plant materials that are uniform and healthy, it is surprising to discover that "hand watering" continues to be the dominant method of irrigation utilized in small to medium-sized operations.

Hour after hour the labor wage clock is ticking, while garden hoses are dragged around from bed to bed. Some plants are watered to the saturation point, while others are simply overlooked when the phone rings or when a customer or co-worker interrupts the routine. By the time the overlooked or over watered plants are discovered, it is often too late and the plants have been put into a stress condition.

Many times, labor expenses and reduced revenue (because of plant loss) go undetected or at least underestimated. As more growers have discovered, it may be time to trade those lost dollars for an irrigation system that covers all plant material efficiently with a minimum of labor.

A Properly-Designed Plan

An efficient greenhouse irrigation system can be fairly simple to install and, in most cases, will cost far less than the labor required to hand water a similar area in a single season. The key ingredient is a properly-designed plan.

The first step in the design is to evaluate the best method to irrigate the designated plant material. Once the areas to be irrigated are defined by size and type of plantings, the system design can be developed. In many operations, it is advantageous to have an irrigation plan that incorporates a variety of systems. Drip irrigation, for example, can be highly suitable when plant containers are over one gallon in size. Greenhouse hanging baskets are also well-suited to drip. When container size exceeds three gallons - and especially if the medium is a soil- less mix - a spray system that covers the entire container surface area is usually more effective. Overhead sprinklers and misters can be an efficient choice for bedding plants, plants in flats and for plant propagation.

Filtration and Water Pressure

Every greenhouse irrigation system should incorporate proper filtration of the water supply to protect small drip or sprinkler orifices from clogging. Any clogging (which may occur if unfiltered water is utilized) will cause disastrous results in uniformity. In the case of drip irrigation, some plant material will not be irrigated at all if the lines are closed by debris.

Pressure regulation is typically used in most greenhouse irrigation systems to ensure that emission devices are operating uniformly and that they are within the specifications of the manufacturer's design. It is typical to have the filter and pressure regulator located near the greenhouse water source. From that point, the irrigation pipeline is usually divided into a manifold, with valves controlling different areas of the greenhouse, or handling different types of irrigation systems within the same greenhouse. Depending upon the level of automation that the greenhouse operator desires, the valves can be manually activated or activated by an electronic, programmable controller. The filter, pressure regulators, manifold and valves make up the "control head" of the irrigation system. Regardless of the type of irrigation pipeline and emission devices which are used, every greenhouse irrigation system should have a "control head" at its water source within the greenhouse.

Greenhouse Piping

The pipeline used in greenhouse systems is usually low-density black polyethylene, schedule 80 PVC or dark painted schedule 40 PVC. Low-density polyethylene has become widely recommended because of its sunlight inhibiting properties, flexibility and low cost. White PVC is not recommended because of the tendency of algae to grow within it. Gray schedule 80 PVC is a good alternative because of its structural capabilities as well as its color and sunlight inhibitors.

Low-density polyethylene is particularly well-suited to drip irrigation and mini-sprinkler irrigation with "punch-in" type fittings. For example, after the proper size hole is punched, low-density poly recovers and seals around the barb of the punch-in fitting, creating a simple leak-free connection to an emitter or mini-sprinkler. The routing of pipeline within the greenhouse will depend upon the type of irrigation system that is supplying the water. Multiple types of systems within the same greenhouse are quite common. Here are some of the most common irrigation applications within a greenhouse:

Greenhouse Hanging Baskets

Hanging baskets within a greenhouse are generally drip irrigated from an overhead pipeline. The pipeline is routed from one or more of the zone valves on the control head, up and along the structural piping that will eventually support the hanging baskets. For this application, low-density poly is almost always used. The poly is strapped to the structural piping every few feet to avoid sagging, then the emission devices are attached with spaghetti tubing hanging down into the basket and supported by either a weight or stabilizing stake.

It is important that the emission devices used are regulated for pressure so that they provide a uniform application of water to all the hanging baskets along the pipeline. Typically, an emission device provides an application rate of .5 gallons per hour. The length of time each zone is irrigated with a hanging basket system is fairly short, and depends on the basket sizes, the plant medium used and the type of plant being watered.