Pipe is one of the best materials for a rack system.
Common galvanized or black water pipe can be
used, but a less expensive choice is slightly thinner
fence pipe. As most greenhouse manufacturers
now use it for their hoop houses, this may be a
good source. It can also be purchased through steel
companies or fencing suppliers.
Pressure treated lumber provides a low-cost,
maintenance-free system. Be sure that it has not
been treated with creosote or pentachlorophenol,
the fumes of which are toxic to most plants. Use
galvanized nails for longer service life. Space
between frames along the length of the rack system
can be 10–12 ft. unless large or heavy pots are
supported. The aisle between racks should be wide
enough for convenient access and plant handling;
2 ft. is a minimum, but a wider distance may be
needed if more light is desired.
Generally, racks are oriented to run north-south
within the greenhouse. This provides equal light to
all the plants as the sun crosses the sky during the
day. Most rack systems are supported on the floor,
and a solid footing is needed to keep them level. The
edge of a concrete walk or a buried solid concrete
block works well. Before attempting to support a
system from the greenhouse frame, be sure that it
will take the extra load. Most crops will add
4–5 lbs./ft2
. (psf) to the structure. Because most