design utilizes pallet trays 4–6 ft. wide by 6–16 ft.
long that are handled on roller conveyors, tracks,
or by a lift truck (Figure 3–6). Trays are moved to a
work area for transplanting, potting, and shipping.
The basic concept of the movable bench system
is to convert all but one aisle to growing space.
The bench tops are supported on pipe rollers and
allowed to move sideways 18–24 in., the width
needed for a work aisle. When there is a need to get
to a particular bench, other benches in the house are
pushed together, leaving an open aisle at the desired
bench. Only one side of the bench can be worked on
at a time. Because the benches move, connections for
water, heat, and electrical systems that are attached
to the bench are flexible. Benches as long as 200 ft.
can be moved easily by turning one of the support
rollers with a crank at the end of the bench.
There are many variations in bench design. Benches
can be fabricated of wood or metal with either a
solid or mesh bottom. Several manufacturers make
an aluminum extrusion that adapts to an expanded
metal bottom. A molded polyethylene grow tray is
also available. The support unit can be made from
pipe, tubing, or concrete blocks. The key to a smooth
working unit is to have metal surfaces for the pipe
rollers to move on.
Plans for 5- and 6-ft. wide benches are shown in
Figure 3–7 on the next page. Dimensions for other
bench sizes and aisle widths are shown in Appendix
VIII. To plan a system for a greenhouse, lay out a
cross section of the floor area on graph paper. Note
the size and location of existing side wall benches,
if any. These can usually remain in place. Place one
aisle next to a side bench. Generally, an 18-in. aisle
can be used with 5-ft. wide benches and a 24-in. aisle
with 6-ft. benches. Adjust the number of bench tops
and their widths to fill the remaining width of the
greenhouse.