Manual, or not?

Thousands of small growers fill containers manually, but this repetitive, time-consuming task can be mechanized to reduce labor and provide a more uniform fill. A question I frequently receive is, “How many containers do I have to fill a year to afford a machine that will pay for itself in a reasonable time?” Use the following tables and formula to get a reasonable estimate.

To calculate the approximate number of containers you need to fill per year, use this formula:

No. containers per year = MC / SPB (HFC – MFC)

Information you will need to know includes the following:
 

MC (initial machine cost): This includes the price of the machine, freight charges, installation and setup. The lowest-cost machines are semi-automatic. Containers are manually pushed on a roller conveyor under a vibrating hopper. The soil falls from the hopper into the container and is leveled with a brush. Maximum rate is about 700 flats per hour, and this process works best with two people. More mechanized container fillers are available from several manufacturers.
 

SPB (simple payback): Simple payback is the amount of time that it takes to recover the initial investment in the container filling machine. It will give a ballpark estimate that will help in evaluating different machines, but it doesn’t account for maintenance or inflation.

Payback should be less than the useful life of the machine. A shorter payback is less risky. Most machines are considered to have a five-year useful life, but it may be longer due to limited use, quality construction and good maintenance.
 

HFC (hand filling cost): This is your cost for filling a flat or pot. This can be determined based on the average number of containers that are filled by one person per hour and the cost of the labor to fill them (see Tables 1 and 2).
 

MFC (machine filling cost): This is the cost of filling the same containers using a machine. Most manufacturers can give you an estimate based on the design of the machine and grower experience. Usually, the manufacturer lists a maximum number, so lowering that value some to account for worker experience, loading the growing mix into the hopper, separating containers, worker breaks, etc. is necessary. Divide the machine rate by the number of operators to get per person rate.

Example calculation: From the table, the cost of handfilling 60 flats per hour at a labor rate of $12/hr is $0.20/flat. The Hand-i-Filler, at a cost of $5,000, will fill 600 flats per hour with two people (300 flats per person) at a cost of $0.04/flat.

If you’d like to get a payback of five years, then you would have to fill 6,250 flats per year:

Number of flats per year = $5,000 / 5 years ($0.20 - $0.04) = 6,250 flats per year

The container filling machine should be considered part of a materials handling system. Storing the empty containers nearby and having conveyors or carts to move them so that walking is minimized will help to keep costs down.

John Bartok is a regular contributor to sister publication Greenhouse Management and an agricultural engineer and emeritus extension professor at the University of Connecticut. He is an author, consultant and a certified technical service provider doing greenhouse energy audits for USDA grant programs in New England.