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Mechanization and Labor Saving for the Small Grower

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Labor efficiency is something to strive for whether you operate a greenhouse by yourself or hire many employees. A good starting point for evaluating labor efficiency is to collect data on which operations require the greatest amount of time. Transplanting, hand watering, plant selection for shipping and moving plants into and out of the growing area are often the greatest labor users. These tasks are the ones that should be evaluated first to see if improvements can be made.

Equipment is available for almost all the tasks that take place in the greenhouse but not all tasks should be mechanized, especially for the grower with only a small amount of growing area. Some of this equipment is very expensive. Other machines have use only a few days out of the year. Purchasing decisions need to be made only after considering many factors.

  • Keep things simple. Equipment or systems that you and your employees understand work best. These generally have less adjustments that need to be made, require less maintenance and use standard parts. It is easier to upgrade a basic system than to replace a complex one that doesn't do the job. I frequently see expensive equipment sitting idle in a corner because it didn't perform the way the grower had hoped.
  • Analyze your needs thoroughly. Equipment is expensive to own. Consideration should be given to where your resources will give the greatest return to the business. For example, an automatic watering system that can be used year-round may be a better choice that a precision seeder that will be used only 10 days a year. Compare alternatives on a simple payback basis. Simple payback in years is calculated by dividing the initial cost of the new equipment by the savings realized per year.
  • Mechanize or automate jobs that are repetitive, tedious or time consuming. Considerable equipment has been developed for most of these jobs. Container filling, plant spacing, moving plants and watering are good examples of this.
  • Install equipment that reduces peak period labor requirements. The spring season and holiday shipping periods are usually the busiest. Carts or conveyors can move plants quicker than hand carrying. These may also reduce the need to hire and manage more employees.
  • Select equipment that will pace workers. Conveyor belts work well for potting, transplanting and packaging providing uniformity and consistency. A variable speed motor adjusts the belt speed for different operations.
  • Reduce the amount of walking that employees have to do. Walking adds considerable time to the cost of plants. An average time to pick up or set down a flat of plants is 1.5 seconds. Carrying or walking can be figured at 4 feet/second. At a $10/hr labor rate, making a round trip 10' away to place a flat of plants on a bench adds 2 cents to its cost. Walking to the far end of a 100' greenhouse costs $0.15. How many times is that flat handled before it is sold?
  • Standardize your operations. Keep the number and types of containers that are used to a minimum to reduce inventory and the time needed to make changes to equipment. Where possible ship in standard units such as carts or pallets. This simplifies loading and invoicing.
  • Consider alternatives to purchasing equipment. Renting, leasing or sharing with a neighbor allows the use of equipment for short periods of time without a large investment.
  • Select equipment that is manufactured with standard parts. Delays in getting special parts to repair a down machine can interrupt a production schedule. Standard parts such as belts, drive chain, pulleys and sprockets can frequently be purchases locally.

Media preparation

Most growers purchase prepared media. A mixer is needed if additives such as top soil, sand or compost are to be added. Used concrete mixers and transit mixers have worked well for some small growers. An alternative is to place materials in layers on a concrete or asphalt pad and use a bucket loader to scoop and dump the materials. This will create a fairly uniform mix.

Container filling

Purchasing prefilled containers is an alternative that may be less expensive than hand filling or owning expensive container filling equipment. Containers are delivered to your greenhouse on shrink-wrapped pallets when you need them.

Flat filler - attaching two short belt conveyors together side by side in an X configuration makes a compact pot or flat filler. One conveyor is fitted with a hopper at the lower end that holds about a bale of growing mix and a chute at the top end to direct the mix to a grated work table about 3' above the floor that supports the container. Excess material falls onto the second conveyor that carries it back to the hopper. Each conveyor has a separate motor. The speed of the conveyors can be controlled by the size of the pulleys used. The unit can be mounted on a frame with wheels for portability.

An economical manual flat filler is available from Golden Pines Manufacturing, 1233 Golden Pines Street, Lamar SC 29069. It operates by pushing the flats under a vibrating hopper filled with mix.

Plug extractors - these low-cost devices loosen the plugs from the tray for easy handling saving considerable time. Standardization of the plug tray is important as a pin plate is needed for each size of tray.

Seeders

Several low-cost seeders that will seed from 1 to 5 flats/minute are available for the small grower. The wand seeder is fitted with needles that pick up seed from a tray and place it in the flat one row at a time. The vacuum template seeder with holes matching the plug tray is connected to a vacuum box. Seeds are released when the vacuum is released. It seeds a whole tray at one time.

Workstation design

A workstation is an area where an employee does a series of repetitive tasks such as transplanting, potting or preparing plants for shipping. The layout of this area can have a large influence on efficiency. A good layout where everything is within easy reach can decrease the labor needed by as much as one-half over a poor layout that requires walking to get materials or to set down plants.

For example, a good hand transplanting rate for 48 cell flats is 20 to 25 flats/hour. Based on a $10/hr labor cost, the cost of transplanting10 flats/hr is $1.00/flat, 15 flats/hr - $0.68, 20 flats/hr - $0.50 and 25 flats/hr - $0.40. Workstation efficiency pays.

The top of the work table should be at elbow height. Height adjustment should be provided for different size workers. It is best to provide for both standing and sitting positions as greater efficiency is achieved when workers change positions.

The reach from the normal arm rest position to get materials should be limited to a 24" radius to the side and front for women and 27" for men. The work area is best if within 16" to 24" of the resting elbow position.

A work station space of 3' x 3' is adequate for most operations. Space to the rear and sides can hold prefilled containers, a cart for placing transplanted containers and movement of the worker. Adequate lighting of 40 to 60 foot-candles over the work area will increase productivity and reduce eye strain. Where multiple stations are employed, a belt conveyor to the front of the workers will carry the completed containers to an area where they can be loaded onto carts for transport to the growing area.

An alternate work station is a movable transplanting table that is placed in the greenhouse next to where the plants will be grown. The table should be kept close to the growing area to reduce walking with the containers. Prefilled containers can be supplied on pallets near the work area.

Carts and wagons

The use of carts can speed up handling and reduce the labor needs. One person can push a cart loaded with 40 to 60 flats from an efficient transplanting area to the growing area next to where they will be placed.

Purchase carts that will roll easily through access doors. A paved walkway down the center of the greenhouse will make movement easier. Select a cart that has large wheels. One that has fixed casters in the center of the cart with a swivel caster in the center of each end will allow the cart to be turned within its own length. Tire size should be at least 2" wide by 6" diameter for use on paved floors and 2-3/4" wide by 10" diameter for use on unpaved areas.

The cart shelves should be made of a lightweight material that is strong enough to carry the load without sagging. A sheet metal or plywood shelf allows easier loading then a wire mesh material. Shelves should be removable and adjustable for different size plants.

There are many types and styles of wagons that are available for greenhouse use. Most contain pneumatic tires for transport over unpaved surfaces. The standard wagon has a fixed rear axle and pivoting front axle on a fifth wheel. Where wagons will be used in tandem in narrow aisles, select a tracking design where both axles are connected together and one wagon will follow in the tracks of the other.

Where the distance between the work area and the greenhouse is greater than two hundred feet, carts and wagons should be pulled in tandem in multiple units to save time. An electric cart or garden tractor can provide the power.

Conveyors

An alternative to moving plants on carts is a trolley conveyor. The system consists of a tubular or angle iron track suspended from the greenhouse or headhouse frame and a trolley-mounted rack that is pushed along manually. Suspending the track over the benches and plants means that no additional aisle space is needed. Curved sections of track are used to get around corners. Switches may be located anywhere in the system to allow transfer from one track layout to another.

The rack should be designed with removable shelves for different size plants. It will hold from 20 to 40 flats at one time. Several racks can be connected together for movement over long runs. Cost of the system is about $3 - $5/linear foot.

Watering tunnel - a low-cost watering tunnel can be made using two or three fan type nozzles attached to a piece of PVC or metal pipe that is suspended over a chain or roller conveyor. Water is supplied to a solenoid valve that controls the flow. A lever type microswitch activates a 24 volt solenoid valve that turns the water on whenever a flat or pot is conveyed under the nozzles. A transformer converts 120 volt electricity to 24 volts to reduce the potential for shock. The excess water can be collected with a pan and piped to a drain or the unit can be placed directly over a drain in the floor.

Watering Boom - for uniform watering it is hard to beat a watering boom. Booms can be simple devices made to operate from a winch pulled cart that supports the boom over the plants. They can also be suspended from track mounted to the overhead trusses. Commercial booms generally have computer control that allows double watering, skipping sections, and multiple nozzles that change the rate of application.

Shipping Efficiency

The following ideas can help improve shipping efficiency.

  • Select a team of two or three employees to gather and prepare an individual truck load. They should be experienced in plant identification and loading.
  • Label or tag plants when they are transplanted to reduce labor during shipping.
  • Limit the number of container sizes and shapes that you use to make load assembly easier. This also reduces the inventory that has to be carried.
  • Develop a plant location identification system that reduces the time needed to find plants.
  • Market plants by full carts or pallets to reduce errors in both assembly and delivery. It also make invoicing easier.
  • Shrink wrap carts and pallets to contain plants and reduce damage.
  • Purchase a hydraulic tailgate to speed loading and unloading of carts.
John W. Bartok, Jr.
Agricultural Engineer
Natural Resources Mgt. & Engr. Dept.
University of Connecticut , Storrs CT

May 2005

Topics: 
Commercial Horticulture
Commercial Horticulture topics: 
Energy
Greenhouse Engineering