Tech Solutions: Potting machines

You can achieve increased productivity, greater uniformity and better economy with a potting machine. These vary from fully manual to fully automatic machines that allow you to put a transplant into a pot at a rate much faster than if you were standing at a work station.

For many growers, the installation of a potting machine has resulted doubling the production rate when potting or repotting plants. Why? Most potting machines hold the container, fill it with soil and then drill or punch a hole for the plant. The operator has only the rhythmic job of setting the plans. One or two other people may be needed to replenish the growing mix and remove the plants.

Besides an increased production rate, the most frequently mentioned advantage to machine-potted plants is uniformity. Because each container is filled and compressed to the same level, feeding and watering can be the same. If a dibble is used, all the plants will be centered, resulting in even spacing across the growing bench.

As with other mechanized production methods, potting machines are more efficient if standardization is practiced. A large run of one size container is better than potting a few hundred of several sizes or types of pots. The time needed to change pot holders and dibble reduces the overall efficiency.

Let’s look at how to make the right selection.

Soil adaptability
The machine should be able to handle your soil mix. A light, moist mix free of clumps is best. Too dry a mix, and the components tend to separate out. Too wet a mix, and the lumping causes uneven filling of the container.
 

Potting machines can handle pot sizes from 2 inches to gallon size or larger.

Container size adaptability
Select a machine that will handle the range of pot sizes you use. Most will adapt to pots from 2 to 6 inches. Some will handle larger ones. Some machines use easily adjustable pot holders; others require replacing the whole set. Be sure that both square and round pots can be filled.

Output
The rate of potting depends on factors such as the size of container, type of plants, growing medium and whether a pot dispenser and dibble are used. The speed of the machine is usually not the limiting factor but rather the skill of the potters. A variable speed is important to pace the workers. Also required is a system for moving plants to the growing area.

Potting machine manufacturers consider that if you grow 100,000 flats per year you can afford a potting machine. At this level of production, the payback is generally two to three years.
 

Home-built potting machine made from two 8-foot-long conveyors.

Portability
In a gutter-connected greenhouse or a range of hoophouses connected by a headhouse, it is usually best to have a fixed machine position. The pots can then be moved by carts or conveyors to the growing area. If you have individual greenhouses it may be more efficient to move the potting machine from house to house. If so, it should be on casters or pneumatic tires.

Operation
Potting machines are most efficient when operated by a crew of several workers. To keep a production rate of one pot every second or two, the materials need to be convenient and in sufficient quantity so that no delays develop. A reduction in rate of only one pot per minute, or a delay of 10 minutes, decreases the day’s output by 500 pots.

At the potting stations, it is important to have operators that are careful about placing the plants or cuttings at the right depth and location in the container.

Maintenance
As with most other machines used in greenhouses, very little maintenance is needed. An occasional greasing of bearings, tightening of belts and cleaning the parts from excessive soil buildup is usually all that is required. Keep a few replacement parts on hand to avoid excessive production loss.

Accessories
Most machines can be fitted with several attachments that increase production or handle different containers. Pot dispensers are available to separate and place the container in the holder. Belt or chain conveyors can be added to move plants away from the machine. Some machines can be fitted with an attachment that allows flats to be filled. This makes the machine more versatile, especially for the small grower producing a wide variety of crops.

For the small grower who is handy with tools, a simple potting machine can be built utilizing two 8-foot-long conveyors. Operated with a foot switch, soil is elevated from a hopper on one conveyor and is dropped into the container in front of the potter. Excess soil is collected from the slatted worktable and returned to the hopper via a second conveyor.

With labor being about 50 percent of the cost of growing plants, it is important to mechanize as many operations as possible. The potting machine is a very versatile machine that will make the potting operation more efficient.
 

Once the pot is filled the soil is compressed, and a screw dibble makes a hole for the plug or cutting.

John Bartok is 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.