Page 17 - Gazette - November 2023

Cost savings in fall and winter production have always been a consideration and many
growers attempt to reduce heating and ventilation efforts to meet financial goals. As the
age-old saying goes, “save now, pay later.” Understanding how relative humidity, heating and
ventilation, and air flow can prevent nutrient deficiencies, disease outbreaks, and various
postharvest problems will ultimately support your most cost-efficient season by securing a
healthy crop. This article will help you to understand common issues that are associated with
improper environmental management during this time of the year include Pythium root rot,
Botrytis, and calcium deficiency.

THE VALUE OF HEATING, VENTILATION, AND AIR FLOW
There are many cultural methods that can be used to modify the production environment
and control humidity. Heating and venting are essential tools to help dry out the greenhouse
during fall when fungal pathogens can thrive. Growers might be tempted to think they are
saving money by avoiding the use of heat, but with improper atmospheric control, growers
will feel more costs long term in increased fungicide inputs, longer production times, and
greater crop losses. Reliable heating and venting systems can be actively used on cold
and overcast days to ensure proper air exchange within the greenhouse. For poinsettia
producers, this becomes especially important during the bract development stage to ensure
adequate expansion. Moreover, when plant canopies become denser with foliage, leaves
can easily trap moisture. Maintaining proper air flow with adequate horizontal air flow (HAF)
and vertical air flow (VAF) fans reduce the chances of disease proliferation. Both types of
circulation fans have different functions. HAF fans work best during the day to circulate
air while the house is benefitting from solar gain, while VAF fans mix the layers of air that
form in the greenhouse at night when cool air stays low in the crop canopy and the hot air
rises into the gable. These valuable tools are complementary as HAF and VAF fans can be
utilized to remove humidity from the plant canopy, while exhaust systems expel humid air
from the greenhouse. Cracking a roof vent or flipping on an exhaust fan in the gable peak
are both effective methods for humidity control. It is also worth noting that although growing
within a “buttoned up” greenhouse environment helps trap in heat on cool sunny days,
photosynthesizing plants can quickly deplete carbon dioxide levels within the growing space
if active ventilation is not used to bring in ambient CO .
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GRIFFIN GAZETTE 2023 | 17