April 2005

Grower 101: Evaluating Plant Handling Systems By John Bartok, Jr.

Reducing plant handling costs is a goal of most greenhouse businesses. Carrying plants is time consuming and heavy work. It is also expensive. There are many systems that can be used to reduce this task and its cost. Purchase decisions should be made only after considering many factors.

Basic concepts

A good place to start is to review some of the basic concepts that apply to plant handling. Consider the different tasks to be accomplished as part of a system that is related to other tasks in the growing process. Then select methods and equipment that reduce handling.

Handle plants in larger quantities.

Use carrying trays that hold 6-15 pots rather than moving pots individually. Pallets, carts and conveyor systems allow more plants to be handled at one time.

Reduce walking distance.

Walking is costly. As you can see from Figure 1, page 38, carrying a flat of plants down a greenhouse aisle adds significant cost. Systems that reduce walking time usually have a short payback.

Standardize your operations.

Limit the number of container sizes and types to reduce inventory that has to be carried and the time needed to make changes to equipment.

Select equipment that is easy to operate and maintain.

Frequently, equipment sits idle because it is difficult to get into proper adjustment. Provide proper training for employees who will operate this equipment. Machines with standard parts available from a local hardware store will make maintenance easier.

Plant handling systems

The following are some typical systems used in the industry to reduce handling labor. These are non-automated and work best for small- to medium-size growers.

Carts:

All sizes of greenhouse operations can benefit from carts. They increase labor efficiency by allowing one person to move more material at one time than could be carried by hand. They are also low cost ($300-600) when compared to labor costs and can be easily expanded as the business grows.

Carts should be selected to fit into the narrow aisles in greenhouses. A 22-inch-wide cart will handle 1020 flats. Standard length is 5 or 6 feet. Most carts have variable shelf spacing to handle different sized plants and containers. Typically, a cart for moving bedding plants will hold 25-30 flats.

A level rolling surface is best for cart operation. In the greenhouse, the main aisle should be paved and a minimum 30-inch-wide aisle down the length of the greenhouse or bay is needed. Larger diameter tires, 6 or 8 inches, will make pushing the cart easier.

The same carts used for moving plants in the greenhouse can also be used for shipping. This will eliminate one or more handlings, saving money. Many larger garden centers now require plants to be delivered on carts.

Monorail:

This overhead conveyor system consists of tubular track suspended from the greenhouse frame. Trolley-mounted racks that carry the plants are manually pushed along this track. Aisle space wide enough to walk in and push the carts is needed.

Curved sections of track are used to get around corners, and switches are located where a transfer is needed from one track to another. The track is easy to install with hangers from the greenhouse frame. Ensure that the frame is strong enough to support a load of plants.

Gantry:

A gantry is a beam or frame, with wheels on both ends, that is supported on rails. It spans over a bay of plants and is pushed by hand. The rails, usually pipe or angle iron, are attached to the sidewall posts and extend the length of the bay. Frequently, pipe rails also are the heat pipes. A gantry can be built with one or multiple shelves to carry the plants. It is also possible, with the use of a transfer cart, to move the gantry platform to the work or shipping area without having to unload the plants. Gantry systems are becoming popular with growers who use a floor production system, as it allows movement of plants without having wide aisles.

Portable belt conveyor:

This lightweight conveyor consists of a powered section to which can be added several slave sections. The sections connect easily and are powered by belts or gears. To change direction of the flats or pots, an adjustable diverter bar is attached. An electric eye can be added to give a count of container flow. The drive unit, an electric motor or gasoline engine, provides variable speed and reversible direction. The conveyor can be placed on legs or on the floor. Moving from one greenhouse or bay to another takes only a few minutes.

Movable plant trays:

These modular trays are supported on a network of pipe rails. The least expensive system of moving the trays from the work area to the growing area is with a track mounted transport cart. Motorized conveyor systems are also available. The trays can be manufactured to fit the space available in the greenhouse. Typical sizes are 6 feet wide x 10-12 feet long. Tray systems eliminate 1-2 handlings of plants.

Comparison

Figure 2, page 40, compares the above plant handling systems based on approximate initial cost and output for a one-half acre, gutter-connected greenhouse (150 x 175 feet) with an attached headhouse. The model assumes the use of 1020 bedding plant flats, with each crop consisting of 12,500 flats that are grown on the floor, except with the movable plant tray system. The average distance that the flats had to be moved from the transplanting/seeding line to the growing area is 200 feet. Labor costs including benefits were considered at $10 per hour. Flat pickup or set down was figured at 11.2 seconds, walking rate at 4 feet per second and cart/monorail/movable tray moving rate at 3 feet per second. The figures shown are for moving a crop from the transplanting or seeding area to the greenhouse. A similar cost is incurred when the plants are removed for shipping.

From the figures, you can see that the costs of systems varies considerably, with the movable tray system being the least expensive. Modifications may have to be made to the greenhouse to adapt some of the systems. The handling cost per flat varies significantly between the least and most expensive systems. The greater the number of crops grown, the shorter the payback.

There are many alternatives in plant handling systems. Before selecting a system, determine how it will fit in with your facility’s layout, cropping schedule, labor force and shipping method.