Root/Leaf Pruning and Ideal Temperature of
Greenhouse Tomatoes
Categories
Information in green provided by the Florida Greenhouse Vegetable Production Handbook, Vol 31
Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication
date December 1990. Revised June 2001. Reviewed February 2008. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.  G.J. Hochmuth, professor of Horticultural
Sciences and Center Director, North Florida Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida. The Florida
Greenhouse Vegetable Production Handbook is edited by George Hochmuth, professor of Horticultural Sciences and Center Director, North Florida Research and
Education Center - Quincy and Bob Hochmuth, extension agent IV, North Florida Research and Education Center - Suwannee Valley, Cooperative Extension
Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.
Root and Leaf Pruning    
   "In addition to side shoot pruning, tomato plants require leaf pruning, and, if in the NFT system, some root pruning. The root pruning is done in the
channel or tube discharge end. Roots will grow into the return system and may clog it if not removed. Roots should be trimmed back away from the discharge
end of the growing channels.  Leaf pruning is required to remove old leaves from the lower part of the plant to improve air movement under the plants and to
make the growing plants easier to manage.
 Leaf pruning is done in conjunction with "leaning and lowering" of the plants. As the plant grows, it soon reaches the trellis cable. At this time, the plant
needs to be lowered so that it can be maintained within the trellis system. Prior to leaning and lowering, about four to six of the oldest leaves are removed. It
is best to clip or hand-snap the leaves from the plant leaving a clean, smooth wound that will dry and heal fast. It is important that fleshy stubs or large
wounds do not result because these are ideal areas for disease organism attack. At the same time, old "spent" fruit cluster stems should be pruned.  Alter
pruning the leaves, the plant is loosened from its cable clip or tie and dropped down allowing new twine to dispense from the ribbon. The plant is lowered so
that there is an 8- to10-inch air space between the floor of the greenhouse and the lowest leaves on the plant. Usually this results in lowering the plant 18 to
24 inches. The plant is reclipped at the cable.
During the process of lowering, the plant is angled along the trellis system on a slant, referred to as “leaning”.   After successive lowerings, the plant stems
will begin to rest on the greenhouse floor. Leaning and lowering (and leaf pruning) is best done on a frequent basis so that large numbers of leaves do not
have to be removed at any one time. Usually every 10 to 14 days will suffice.
When leaning and lowering, workers must ensure that no damage occurs to the stems such as snapping or crimping. This is a problem as the plants are
lowered and angled around the end posts in the trellis system. In addition, fruits should not be punctured by stems as the stems are lowered. After the
pruning is complete, all leaves are removed from the greenhouse to a disposal pit away from the house. The floor should be swept clean of any trash and
debris from the pruning processes. After leaf removal, but before lowering, is a good time to apply labeled pesticides (if needed), since good coverage can
be achieved.

Temperature Control
Tomatoes grow and yield best when night temperatures are 62 to 72oF and day temperatures are about 80 to 85oF. For economic reasons, maintaining the
night temperatures at 65oF is best. At this temperature, diseases such as Botrytis (gray leaf mold) are reduced, and tomato yields and fruit ripening are
satisfactory. Night temperatures should not be allowed to drop below 60oF. At these low temperatures, Botrytis is favored and blotchy ripening is increased.
Growers need to watch the weather especially in the fall and late winter when heating requirements are sporadic. Heaters need to be checked to make sure
the pilot lights are operating and that the heaters function properly, even during these sporadic heating periods. Heaters should be cleaned and checked at
least yearly for operation efficiency.  Heating can be made more efficient through several factors that growers can control. First, the heaters must be
operating correctly and ventilated properly. Improper operation can waste fuel and incomplete burning can produce ethylene gas that can severely damage
greenhouse tomatoes.
  A second factor that can increase efficiency of heating is the installation of ground or floor air distribution of heat.  Since heat rises, it does not make
efficient use of heat to distribute it in a ceiling distribution tube. Growers can install a manifold duct on the fan and direct the heated air onto the floor via
stove pipes and clear polyethylene tubes. The tubes can be placed under the plants between the twin rows. Another factor that can be included here is a
heat retention cloth, similar to a shade cloth. The heat retention cloth is installed just above the trellis system and deployed during nights when heating is
used. A 1.5 to 2.0 ounce per yard polypropylene cloth can be used for this purpose. Heated air will be trapped in the plant canopy instead of rising into the
greenhouse ceiling. Shade/heat retention cloth deployment can be automated and controlled by a computer.   Distributing heated air on the floor helps warm
the root zone and reduces condensation on the leaves and fruits.
A third factor that helps obtain better growth is the installation of motorized shutter vents for winter ventilation. The shutter vents are installed in the end wall
above the cooling pad. With the vents in place, the pad can be closed off completely in the winter and reduce cool air from entering the greenhouse. This
helps make night heating more efficient even compared to situations where growers place plywood or styrofoam sheets loosely against the pad on cold
nights."
(Excerpt from Mississippi State University Extension Service "Greenhouse Tomato Handbook"
Temperature: A day temperature of 70 to 82 °F is optimum, while night temperature of 62 to 64 °F is optimum for greenhouse tomatoes. During cloudy weather, a temperature closer
to the lower end of these ranges is preferred, while in sunny weather, temperatures closer to the higher end are better. Below 60 °F, nutrient deficiencies may occur because plants
cannot absorb some elements at cool temperatures. The first sign of cool temperature stress is purpling of the leaves, indicating lack of phosphorus uptake (even though there may
be adequate phosphorus in the nutrient solution). One or two nights of 56 or 58 °F temperature can cause a considerable number of rough fruit several weeks later when fruit
exposed to the cold temperature reach full size. You should maintain a minimum temperature of 64 °F. Ideally, the thermostat should be located at blossom height rather than above
the tops of plants.
Avoid temperatures over 90 °F if at all possible. At 86 °F, lycopene (the pigment that makes tomatoes red) no longer develops. See the section Greenhouse Cooling for help in
managing high temperatures.
Locate thermostats near the center of the greenhouse for good temperature control. Also, enclose the thermostat in an aspirated box, or shade it so that it indicates the air
temperature correctly. If the sun is allowed to shine directly on the thermostat, it will read a higher temperature than the air surrounding it.)
   "Ventilation and cooling is needed for tomatoes to reduce heat scalding on fruits. Tomatoes perform best if the day temperatures do not rise above 85F.
This temperature is impossible to maintain in the fall and spring without some type of shading.  The majority of cooling on warm, dry days is achieved by
exhaust fans and evaporative cooling pads. Shading by greenhouse shade paint or cloths is needed to reduce the heat load in fall and spring when
temperature and humidity are high.  Shade cloths (white or reflective cloths) installed in the house above the trellis are more flexible than the white
greenhouse shading paint. Shading should be present for the planting of the crop and removed about November 1. Spring shading should be installed by
the first of March.
The degree of shading will range from about 20% early to about 50% during the hottest part of the season. The plastic greenhouse cover alone can shade
anywhere from 10% to 20% depending on type and age. A system that has worked in Florida involves both a ceiling cloth and a trellis-height cloth. The
ceiling cloth is a 30% polypropylene cloth that follows the inside contour of the ceiling suspended on cables. The second cloth over the trellis is a 20%
polypropylene cloth. Shading can start with the trellis cloth in early March. By the middle or end of March, the ceiling cloth alone is used. Then, both cloths
will be needed by the middle or end of April.
Shade cloths can vary from white polypropylene materials to reflective, specially designed shading materials. Polypropylene "row covers," obtained locally,
appear to function well, and are inexpensive. They are satisfactory for the small grower. Larger growers may be more efficient with a computer controlled,
specially-designed shading system. A key to effective shading is to cover 100% of the crop area. Placing strips of a cover in the house does not effectively
reduce fruit sunburn. Furthermore, complete cover installation reduces the amount of air the fans must exhaust to achieve cooling. This is because, with the
cover in place, only air in the plant canopy (below the cover) is exhausted.
  Ventilation of the tomato house is still required on most days in the winter. This is where the motorized shutter vents are very useful. During December,
January, and part of February, the cooling pad can be closed off. The shutter vents are then opened by thermostat or controller just before the first fan
comes on. Cool air from outside is drawn in through the vents rather than the cooling pad. The cool air is drawn in over the top of the crop instead of directly
onto the crop if the cooling pad was used. Cold air drawn through the pad directly onto the crop reduces growth and seriously reduces the size and quality of
fruits."
  ..."The key for successful tomato production is to begin heating and cooling on a timely basis. Tomatoes perform best when temperature regimes are
uniformly controlled. Wide fluctuations in temperatures lead to fluctuations in growth rate and eventually give rise to poor fruit shape, color, and increased
fruit cracking. Attention to efficient designs and operation of heating and cooling systems will pay off.