Every year I see more and more greenhouses built for tobacco transplant
production. Farmers grow plants for their own use as well as selling to
their friends and neighbors. The initial cost of a greenhouse is a bit
of an investment no matter what it will be used for. A greenhouse gives
the grower greater flexibility in what he wants to grow and when he wants
to grow it. What great potential! What advantage one has with a growing
structure such as a greenhouse.
Tobacco growers use their greenhouses for approximately 3 months and
allow them to sit empty for 9 months. It seems senseless that Kentuckians
are satisfied to let California, Florida, or any other state continue to
dominate the vegetable market in this state. Why not use tobacco greenhouses
to cash in on some of the vegetable and flower market in the off season?
My goal IS NOT to get tobacco farmers to stop growing tobacco in
their greenhouses. My goal IS to help tobacco growers realize that their
houses can be used to grow other crops when they are not growing tobacco.
Growers can diversify their crop productiohn and increase their income.
Why let a growing facility with such great potential sit empty and non-productive
for as much as 9 months out of the year? With slight modification in the
float bed system, greenhouse tobacco growers can shift gears and start
growing other crops with basically the same equipment and style of growing
that they currently use. Innovation and change can be benefical but does
not have to be expensive. With this in mind, I would like to introduce
the "RAFT" system.
Using the "RAFT"(Revised Agriculture
Float Technology) System
The "RAFT"
system uses established float beds, outdoors or in the greenhouse, as the
primary growing area. We use the standard "float" (polystyrene,
Speedling tray or Todd tray) tobacco trays, turn the trays upside down
and float them on the water. This gives a 2" thick table floating
on the water. The floating bench can also be made by floating 1",
1.5" or 2" commercial insulation board (blue
board or extruded polystyrene - Styrafoam). In the typical float bed
system, the plants are in trays floating in the water and the cells of
the trays are saturated with water constantly. The tobacco plants seem
to do well in this type of environment, however, most plants do not like
a constantly saturated soil. Often seed will not germinate, or the plant
will not grow normally due to root, stem and leaf diseases.
In the RAFT system, an absorbent fabric,
known commercially as capillary mat, is laid over the floating polystyrene
trays with about 2" to 6" of the mat hanging down in the water
all around the raft of trays or insulation board.
Next, a root barrier fabric (Weedex, a landscape fabric, or Hang Loose,
a tightly woven fabric for lining in clothing) is placed over the mat to
keep the roots of the plants from growing into the mat. The root barrier
helps reduce water loss from the surface of the mat by evaporation. The
RAFT is now complete and ready for growing plants.
The key to success with the RAFT system is that growing medium in the
pots placed on the surface of the float table have good contact with the
mat. This allows good wicking of the water into the pot by capillarity.
As the plants mature, the roots will grow out the bottom of the pot and
onto the surface of the mat. Plants to take the water they need from the
surface of the wet mat.
In our trials with the RAFT system, I grew plants in 8" mum pots,
24 - 2 1\2" cell plug trays, 4" square pots (JPEG
PHOTO) and various other small market packs. In my observation of how
plants grew in the different containers, I concluded that the 8" mum
pots worked best. I also found that the mum pot gave a solid, stable base
that did not turn over easily when the plants got larger and top heavy.
I found that the mum pots help set the correct spacing needed for individual
plant growth. The pots had a good flat bottom, with holes in the bottom
and bottom sides. This allowed good contact with the mat and water was
able to wick from the mat into the pot. (JPEG
PHOTO)
In our trials, the different size containers were filled with Scotts'
Metro Mix 510 commercial growing medium. This medium was light enough for
good air infiltration so the media was not soggy. All commercial growing
media and many types of potting soil should work to grow plants in the
RAFT system.
I grew a number of garden plants using the RAFTsystem - beets, carrots,
cilantro, collards, kohlrabi, lettuce, mustard, parsley, spinach and turnips.
I concluded that the "leafy" vegetables did well with this system.
However, some root vegetable crops such as beets and turnips did not form
the typical swollen root within the "days to maturity" time frame.
Radishes and carrots did mature in the time frame. For those root vegetables,
who's tops are used for greens, such as beets and turnips, the tops were
mature in the days to maturity time frame and could be used.
--- Mark Showalter, December 1997.
Cooperative Extension Service --- University
of Kentucky
