Greenhouse Tomato Environmental Control
and Pollination
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.
"Environmental Control
 Temperature management is very important for successful tomato crops. Poorly controlled temperature regimes can increase disease problems and lead to
fruit color and quality problems. Tomatoes produce the largest yields of highest quality fruits when day temperatures are in the range of 80 to 85F and when
night temperatures remain above 62F, but below 72F.
Excessively high temperatures can lead to poor fruit color (orange instead of deep red). High localized fruit temperatures (sun scald or sun burn) from
excessive radiant energy on fruits can lead to yellow areas that never turn red. This symptom is referred to as "solar yellows." Unmarketable fruits result. On
some cultivars that have the "green shoulder" genetic background, excessive fruit temperature seems to enhance the greenshoulder expression. These
fruits often will not develop uniform red color and the shoulders often become rough and cracked. High temperatures (above 90F) also result in poor
pollination and reduced fruit set.
Low temperatures also cause problems with fruit quality. Fruit set and fruit smoothness are sacrificed when night temperatures are maintained below 62F.
Cat-facing is often more prevalent in houses where night temperatures are low (Fig. 10). Low night temperatures and low light intensity have been
associated with increased incidence of blotchy ripening where fruits fail to form uniform red color. Cool temperatures (below 60oF) enhance the activity of
gray mold (Botrytis) disease. Temperatures allowed to drop below 50oF may result in fruit chilling injury where fruits are damaged by the cold temperatures.
Low Temperatures also reduce flower production.  Temperature control is achieved by use of various systems including heating furnaces, exhaust fans,
evaporative cooling pads, and shade cloths.

(Excerpt from Mississippi State University Extension Service "Greenhouse Tomato Handbook"
Relative Humidity:  The optimum relative humidity for greenhouse tomatoes is 60-70 percent.)

Humidity control is relatively more difficult to achieve in Florida. First, the relative humidity is usually adequate or high in contrast to the extremely low
humidity prevalent in northern and desert climates. Controlling humidity is made more difficult by the fact that Florida greenhouses are ventilated frequently,
even in the winter. Increasing humidity in winter through the use of inexpensive humidistats that operate the evaporative pad has not been successful
because of the poor quality humidistats. They usually are not accurate and are very prone to failure. Furthermore, when the evaporative pad is used for this
purpose in the winter, there is often excess cooling because cool air from outside is drawn into the house. If more humidity is required, a fogging system
would be a better choice."...
" Shading in Florida can be a 2-tier system where a 30% to 40% shade cloth is used over the house or on the inside on cables following the contour of the
ceiling. The second cloth would be a 10% to 20% cloth over the trellis at plant height. Shade systems inside the house on cables have an advantage of
being movable so shading can be removed during cloudy periods.  Shade cloths can be made of knitted or spun bonded polypropylene for the least expense
for small houses. Plastic sheets are not as desirable and they collect water from condensation. There are several very good commercial shading systems for
installation inside a greenhouse, some of which can be automated.
Carbon dioxide (C02) enrichment of the winter greenhouse environment is a question many growers have. Research in northern climates has shown that
raising the CO2 level from the normal ambient level of 350 ppm to 1000 ppm often results in increased yield. Effective use of this technology requires that
houses be closed for long periods each day. The frequent need for ventilation of the greenhouse, even in winter in Florida makes CO2 enrichment a very
questionable practice. The problem is that high levels of CO2 cannot be maintained for more than an hour or so on most days before the exhaust fans are
needed.

Pollination
Tomatoes are self-pollinated; pollen from a flower pollinates the same flower. To accomplish pollination, pollen must be loosened from the anthers and
dusted onto the stigma. Outdoors, wind assists in pollen dehiscence, but in the greenhouse, the flowers must be vibrated. Without vibration, poor fruit set,
shape, and size could result.
Pollination is achieved by vibrating the flower cluster for a second or two with some sort of electric vibrator. Some beginning growers use back massagers,
electric toothbrushes, etc., but one of the most satisfactory tools is a pollinator (battery operated) made specifically for the purpose of pollinating. This
equipment results in less physical damage to the flower clusters and young fruits than some of the homemade mechanisms. Another method that seems to
work well is a handheld electric leaf blower. This is one of the quickest means to effect pollination. Since it is quick, growers are more likely to use it daily.
Pollination should be done at least every second day. Vibrating is not effective on cloudy days because the humidity prevents pollen dehiscence even with
vibration. However, it might be a good idea to pollinate every sunny day in the winter. This will avoid missing several days on end if the "skip-day" is sunny,
but the next pollination day is cloudy. Therefore, every-day pollinating lessens the problems caused by cloudy days.
Pollination should be done during the daylight hours of 10 AM and 3 PM. Greenhouse humidity is lower at this time so that pollen dehiscence is highest. In
addition, fruit size seems to be maximized by pollination during these hours. This is probably related to the increased amount of pollen available during these
hours. When pollinating a cluster, it is important to be careful not to touch developing fruits since the slightest scrape can result in a serious fruit scar as the
fruit enlarges.
Pollination is time-consuming (about 20 to 30 mins for 1000 plants), and it needs to be accomplished during a fairly rigid time span and with regularity. These
problems have caused some growers to devise automatic vibrating systems in the house that vibrate the whole trellis system.  For small-size tomato
producers, an effective pollination method is the air-blast sprayer or leaf blower. These blowers can be directed at the flower clusters to vibrate them and
loosen the pollen. The blower system is very fast and appears to be as effective as individual flower vibration.
This vibration technique usually consists of an electric cam vibrator attached to the trellis system through a common cable. Automatic vibration requires that
extra strong (airplane) cable be used for the trellis so that it can withstand the vibration without snapping. Plants need to be fastened tightly to their strings
so that vibration is efficient. The automatic system is then operated by a time clock. Vibration can be set for a few seconds (5 to 10) daily. Another option
might be to vibrate once for a few seconds at 11 AM and then again at 2 PM. This technique would help the pollination on days that are foggy in the morning
but clear up by noon.
Automatic vibration seems to work well for individuals who have tried it, but it has its drawbacks. Since the whole plant vibrates, all flowers on the plant get
pollinated, even the very late flowers developing on the lower parts of the stem. These flowers are usually left behind in a hand-harvested house and do not
form fruits. In an automatic house, these flowers will usually produce fruit but the fruit will small, poorly shaped, late in maturity, and likely to blotchy-ripen.
These problems arise because competition between these late fruits and the other larger fruits already set in the cluster. As a result, operators who use
automatic pollination must pay much closer attention to cluster pruning to remove these undesirable fruits.
Another potential problem with automatic vibration is physical damage to the plant stem from scars where the string and stem rub together. Continual
abrasion may provide wounded areas for disease organism attack. Excess vibration periods or violent vibrations also could snap tops out of tender plants.
Plants vibrated excessively (more than 60 seconds per day) might slow down in growth rate since vibration is detrimental to the growth process.
Recently, certain species of bumble bees have been used in greenhouses for pollination. These bees are commercially cultured and supplied to the grower.
Bees are economical pollinators for growers with more than one-quarter acre of tomatoes. Hives are usually active for 6 to 10 weeks, and then must be
replaced. Hives cost from $100 to $150 each, depending on bee population of hive."