Off the floor

The greenhouse bench system can cost more than the greenhouse frame. Besides getting the plants up to a working height, benches provide better drainage and allow air movement for more uniform heat and better ventilation.

The most common support for the bench top is galvanized steel tubing or pipe. This has a long life and is easy to construct. A less expensive alternate is concrete blocks with tubing or pressure treated lumber runners. Bench tops can be fixed in a conventional or peninsula arrangement or movable to increase growing space. They can also be mobile and handled on conveyors or carts.

Bench tops can be made of materials, wood, plastic, wire mesh, or expanded metal. The material should be strong without sharp edges and sag so the containers remain level. The containers should also slide easily, resist corrosion, be without sharp edges, and install easily.

Wood

Used pallets are modular and available in several standard sizes. They provide adequate support for the plants, but the life is limited and the edges often break from use. Snow fence is used by some growers. This has stained ?-inch x 1½-inch slats and is available in 4-foot x 50-foot rolls. It is easy to roll out on the bench supports.

To get a longer service life (20 years or more) select pressure treated lumber. Home centers and lumber yards usually carry ACQ (Alkaline Copper Quat) 1-foot x 6-foot lumber or 5/4-inch x 6-inch decking. Nails and screws need to be specially treated to reduce corrosion. Long-life wood such as cedar and cypress are too expensive for large installations.

Another expensive alternative is composite lumber made from sawdust and plastic. Strong and easy to fabricate, their use is generally limited to garden centers.
 

Welded wire

This low-cost option that makes a good bench top if adequate support is provided. It is best to use a 10- or 13-gauge wire with a 1½-inch x 1½-inch mesh to avoid too much sag. Purchase wire mesh that has been galvanized after welding. Welded wire can also be obtained with a colored plastic coating to give a better appearance. Welded wire can also be formed into self-supporting bench tops (Channel Top) that eliminates the need for cross frame supports.
 

Galvanized expanded metal

This is the most common material for strength and long life. Available in widths from 2 feet to 6 feet in panels to fit standard benches, metal thickness is usually 13 gauge. Standard material needs to be supported on 24-inch centers. The expanded metal is frequently inserted into an extruded aluminum frame requiring little maintanance.
 

Plastic

Tops molded from recycled polypropylene plastic are easy to assemble and provide protection from chemicals and rot. They are available in several colors. Typical panel size is 1½-foot x 3-foot or 2-foot x 4-foot. Interlocking tabs hold them in place. With heavy plant loads, the top may sag if not supported properly. Cost is competitive with the metal materials.
 

Troughs

These aluminum or plastic channels are placed on supports that pitch from an irrigation supply end to a sump. They are best adapted to pot plant production and are available is several widths.

Ebb and flood

These molded trays have grooves and a sump for drainage. They can be self-contained or inserts placed into an aluminum frame. The trays are frequently manufactured from recycled plastic.

Bartok is a regular contributor to 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.

Have a question? You can write John at jbartok@rcn.com.