Tech Solutions

Maximize space with movable tray systems

Gutter-connected greenhouses have the advantages of lower energy costs, better space utilization and more uniform environment. They put all the growing under one roof allowing better materials handling and easier shipping.

To get maximum use of space, movable tray systems are often installed. The basic concept is to install trays over the whole greenhouse area except for one movable aisle that is used for tending the plants. The trays are supported on pipe rollers and allowed to move sideways 18 to 24 inches, the width needed for a work aisle. When you need to get to a particular growing tray, the line of trays is pushed aside, leaving the work aisle.

Because the trays move, automatic watering, bottom heat and electrical systems have to be supported from the floor or the bench supports. Tray lines as long as 200 feet can be moved by turning the support rollers with a crank at the end.

Moving plants in and out of conventional bench systems is labor intensive. Walking with one flat or a couple of pots at a time adds considerable cost to the plants. Walking 25 feet, picking up a flat and walking back to a cart takes about 23 seconds. At $10/hour this adds more than 4 cents to the cost of that flat. This cost is added every time the flat is moved.

Tray systems
The tray system saves considerable labor as the plants don’t have to be carried to a cart or conveyor. Trays are usually loaded with potted plants or flats in the headhouse then moved to the greenhouse. They can be moved back to the headhouse for spacing or maintenance. When ready for marketing, they are moved to the shipping area. Some growers ship directly on the tray saving additional handling. Tray systems have the shortest payback the more times plants have to be handled. Tray size is usually 5 to 6 feet in width and 8 to 20 feet long. The trays should be designed to fit the type of growing container that you use and the space available in the greenhouse. They can also be designed for an ebb and flood system with recycled water.

Two types of tray transport systems are common. The roller conveyor system uses flat bottom trays that ride on trolley wheels or fixed casters attached to support rails. The trays are guided by the design of the support wheels attached to the rails.

In the second system, the rollers are attached to each tray and ride on the smooth pipe rails. One set of rollers provides the guidance and the other is just for support.
 

Transport cart — To get the trays from the headhouse to the greenhouse, a transport cart can be used. This low-cost cart travels in an aisle along the end of the tray lines. A tray to be moved is rolled onto the cart and locked in place. The cart usually has four support casters and a guide wheel. This wheel follows a rail mounted to the floor to guide the cart as it is pushed. The cart needs to be designed to fit the size of trays. It can be designed to carry one or two trays at a time. Cost of the transport cart is $2,000 to $3,000.

Transport conveyor – This system uses rails with attached plastic trolley wheels to move the trays. The system is designed to support flat bottom trays. An alternate system uses rails that support trays with wheels mounted to the underside. The transition from one direction to another requires two sets of wheels. Manual or pneumatic lifters transfer the tray from the growing area to the conveyor. Movement to or from the growing area is usually done manually. Several trays can be pushed at a time by one person.

A computer-controlled, motorized system is available but not common in the U.S. In this system, multiple trays are loaded onto a transfer cart. A growing location is designated by the operator and the cart is automatically moved to that location. Trays are off-loaded automatically. The computer keeps a record of the location so that it can find them when they are ready to be shipped. A system such as this can handle up to 150,000 locations in the greenhouse.

Considerable labor is required to handle plants from the time the containers are filled until the time the plants are shipped to the garden center. Although a tray system costs $10 to $20 per square foot, the payback is fairly short due to the significant savings in labor.