The benches of a greenhouse may be raised or at ground level. They may actually contain the crop or merely support it. The style of benches, materials used, and arrangement within the greenhouse all depend on the crop being grown. However, regardless of the crop grown or style of bench selected, greenhouse benches must fulfill three functions:
1. They must drain quickly.
2. They must be of a width that allows workers to reach into their center.
3. They must maximize the crop’s exposure to light.
The choice of bench styles depends on the crop being grown. For example, greenhouse vegetable production (principally of tomatoes and lettuce) requires ground beds. Production methods are similar to those used in field plantings, but the ground beds need special preparation for proper drainage. Such preparation includes approximately six inches of crushed stone beneath six to eight inches of porous soil, and a properly installed drainage tile system to provide for subsoil drainage. Similar bed construction is required if the ground benches are used for cut flowers such as roses. The benches are usually limited to three feet in width to allow access to the center of the bed by workers who must tie
figure 19-17. These roses are being grown in ground beds as a cut flower crop. (Delmar/Cengage Learning. Photo by Jack Ingels.)
the crop, cut the blossoms, and so forth. Sides may be built as an edging for the ground beds to define walkways more clearly and reduce the possibility of plant injury (Figure 19-17).
Raised benches are used in the production of pot crops as well as cut flower crops. In the case of potted plants, the bench serves much like a table to bring the crop up to a level where it can be worked on easily. With cut flower crops, the bench not only elevates the crop but also contains the growing medium for the plants. As such, it must be from 6 to 12 inches deep to allow for proper root development and drainage (Figures 19-18 and 19-19). Raising the bench above ground allows air to flow more freely around the crop and permits a warmer root-zone temperature to be maintained. Often, heating lines are placed beneath the benches to attain maximum benefit from the warmth.
figure 19-18. A bench for potted plant production (Delmar/Cengage Learning. Photo by Steven Newman.)
figure 19-19. A cut flower bench must be from 6 to 12 inches deep to permit root development and proper drainage. (Delmar/Cengage Learning. Photo by Jack Ingels.)
figure 19-20. This photo illustrates the pipe frame. (Delmar/Cengage Learning. Photo by Jack Ingels.)
A framework of pipe constructed above a regular bench increases the amount of growing space within a greenhouse by permitting hanging baskets to be grown above another crop (Figure 19-20).
Greenhouse benches may be purchased as prefabricated units or improvised by the grower to fit particular needs. The most important quality of a bench is capacity for rapid drainage. A number of materials are commonly used:
• wood (rot resistant choices such as redwood, cedar, or cypress are durable but expensive)
• aluminum (very durable and expensive)
• welded wire fabric
• wooden slats (less durable and less expensive)
• spruce or redwood lath with concrete block legs
• concrete (long popular for ground beds, it is both durable and expensive)
• polypropylene tops on a support frame
Wooden supports, metal pipes, concrete blocks, and wire fabric or lath can be combined easily to make an affordable bench that can be adapted to all types of containerized crops. Care should be given to preserving any wood used in bench construction. Either naturally rot – resistant woods such as redwood or preservative-treated woods (stained with cooper naphthanate) can be used.
Aisles along the sides and between the benches: least efficient use of space for growing.
figure 19-21. A cross-bench arrangement (Delmar/Cengage Learning)