Pruning, Training, Thinning, Fertilizing, and
Irrigation of Greenhouse Tomatoes
Categories
Information 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.
"Pruning and Training
   Greenhouse tomatoes, as a result of their indeterminate growth habit, require continuous pruning and training to the trellis system. The trellis system
consists of wire cable stretched from one end of the house to the other between two anchor posts. The anchors should be metal posts cemented into the
greenhouse floor. A counter support, deadman will help strengthen the end posts. The cable is stretched tightly over each row of plants at a height of 8 to 10
feet and fastened on one end to a cable tightener. The downward pull exerted on the cable by a single tomato plant with five or six well-developed clusters of
fruit might be 10 to 12 pounds. Therefore, extra supporting posts will be needed every 20 to 30 feet down the row of plants. Cable diameter should be at
least 1/16 inch with 3/32 inch preferred.
Plants are trained up a string attached to the cable above the plant and extending to the base of the plant. Trellis strings are made up ahead of planting,
keeping in mind that a 10-month-old tomato plant might be 30 feet long. Different growers have individual preferences on the technique to use to attach the
string to the trellis cable and the resulting facility for quickly releasing the plant to lower it. One system is to roll the extra "future" twine in a ribbon or ball and
hang it over the cable with enough extra twine to enable the ribbon to dangle. The downward string is then clamped to the upward string by a plant clip.
Another option is to attach the string to the wire via a slip knot that can easily be released. There are also commercially available metal string bobbins on
which to wrap the twine and which also function as a hanger, or a notched spool with a hook.  String used for trellising should be strong plastic or
polypropylene twine. Polypropylene hay baling twine and tomato staking twine work well and are about the least expensive products available. In addition,
they can be secured locally.
 To start the procedure of trellising the plant, the lower end of the twine is loosely fastened to the base of the plant. This operation usually starts when the
plant has 6 to 8 large leaves and before the plants start to topple."..."The first method involves using plastic plant clips (1 inch size) available at most
greenhouse supply outlets. The twine is clamped in the hinge of the clip and the clip is snapped around the plant stem just below a large leaf. It is not a good
idea to clip at the flower cluster node since the flower cluster stem might be crimped and damaged. Clipping is done every 3 or 4 leaves to keep the plant
tops attached to the twine.
 The second system involves the use of a plastic ribbon tape in place of most of the plastic clips.  The ribbon can be applied by a hand fastener machine
(tapener) that wraps the tape around the twine and plant stem and staples the ribbon.  This method is much faster than the clipping method. However, some
clips still must be used since, in the tape method, the plant stem is free to slide down the twine. A clip, fastened just below a leaf, is used every three or four
tapes to keep the stem anchored to the twine."...
 "Greenhouse tomatoes require pruning of all lateral branches (suckers) as they develop to encourage a single leader.  Pruning helps in the overall
management of the long-term tomato crop. Pruning must be done on a frequent schedule (every 3 to 4 days) so that only small side shoots are removed.
Excessive intervals result in large shoots that are difficult to remove, resulting in serious damage to the plant and increasing the likelihood of disease
Pruning is best done early in the day when plants are turgid but dry. Suckers snap out of the leaf axils easily, resulting in a clean wound that heals easily.
Growers need to be careful to remove only suckers and not the main terminal bud. Sometimes, this is difficult to do when several suckers are present in the
top of the plant. During sucker pruning, any leafiness in the flower cluster should be pinched out. Pruning early in the day allows the wound to dry sufficiently
during the day making it less susceptible to decay organisms. It is best not to prune during cloudy periods because drying of the wounds is not optimal.  The
pruning time should be used to inspect plants or obvious problems, such as disease, nutritional problems, insects, etc. All pruned plant material should be
placed in a container or bag and removed from the greenhouse.

Cluster Thinning
  Tomatoes produce anywhere from one to about 10 flowers per flower cluster.  Under good pollination conditions, about six to eight of these flowers might
form fruits. For many cultivars, especially large-fruited cultivars, this is too many fruits to develop properly. If too many fruits are allowed to set on a cluster,
fruit size, shape, quality, and uniformity are sacrificed. Shape is sacrificed because excessive numbers of fruits in a cluster cause compression damage to
neighboring fruits as they develop. Quality is reduced because of the poor shape and because the small, later-setting fruits are prone to blotchy-ripening.
Nonuniformity results because maturity occurs over a long period and may overlap fruits on higher clusters.
    To alleviate these fruit problems, tomato clusters should be thinned to provide an optimum number of fruits per cluster.  If the cultivar has the capability to
produce high yields of large fruits, and this is the goal of the grower, then clusters should be thinned to three to four fruits. Cultivars with intermediate fruit
size can be thinned to four or five fruits.  Rarely will leaving more than five fruits in a cluster pay off with the large or medium-size fruiting cultivars. Clusters
should be thinned to the lower number of fruits in winter period.  Those cultivars being grown for “cluster” tomatoes where the entire cluster is harvested at
once may need some thinning to remove off shape of extra, very small fruits. Small fruited “cluster” tomatoes may not need thinning.  Cluster pruning should
be done about once per week. This allows several fruits in a cluster to set so that a choice can be made regarding which to remove and which to leave. The
objective should be to thin the cluster to a group of fruits that are most uniform in size and age. Cracked fruits and misshapen fruits should be removed no
matter the size.
    When cluster thinning, workers must be sure to take care not to rub or scratch fruits to be left. Small abrasions early in fruit development result in large
scars at harvest. It is a good idea to check clusters a week or two later to remove any small fruits that developed since the previous thinning. If automatic
vibrating pollination systems are used, cluster thinning will play a large role in achieving good fruit quality.

Fertilizer
Tomatoes require close attention to fertilizer programs so that high yields of high quality fruit result. Growers should learn to fertilize the crop by the parts per
million (ppm) method rather than by the soluble salt method."..."Fertilizer management is a part of the production practices that can be easily managed when
the basics are understood. On the other hand, poor fertilizer management can lead to serious quality problems that take long periods to correct. Good
management also applies to the methods growers choose to dispose of fertilizer waste water. Risks to groundwater from leaching of fertilizer is an actively
debated issue and greenhouse operations will not be exempted.

Irrigation
Greenhouse tomatoes require large amounts of water, using 1 to 2 quarts of water per plant per day during peak growing periods.  Although tomatoes
require large amounts of water, they also are extremely sensitive to flooding damage. If tomato roots are flooded (even if only for a few hours) damage to
roots occurs and infection by the Pythium root rot organism is possible. Root flooding is an extremely common problem in greenhouses in Florida, especially
in the NFT systems in north Florida.
One of the keys to successful irrigation management is correct timing of water application. Amounts and frequency of application change through the
season. In non-circulating systems (perlite, rockwool, bag, trough), water applications need to be more frequent as the plants develop. In NFT systems,
irrigation frequency might actually need to be reduced, especially in the small 4-inch tubes because roots block the channels causing water to pool and rise
up to flood the roots. This is a serious problem and a limiting factor in the 4-inch PVC system."...  "Irrigation management problems need to be taken into
account when deciding an investment in a particular growing system.