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is very important when trying to prevent pathogenic
fungi. Put another way, if humidity levels are kept
in check, the pathogenic fungi’s ability to establish
is hampered. The optimal humidity range for indoor
gardens and hobby greenhouses is 50-60%. Even
when an indoor garden is climate controlled by
a mini-split air conditioner, a dehumidifi er may
have to be used to maintain the optimal humidity
level. Again, it is important to remember how
the garden’s temperature also affects the relative
humidity levels. Controlling temperature variances
will reduce spikes in humidity. A grower who
invests in an atmospheric controller, which can be
used to automate fans, air conditioning equipment,
and dehumidifi ers, will have a much easier time
maintaining the optimal temperature and humidity.
The controlled, consistent temperature and humidity
levels are a strong defense against pathogens.
AIR PURIFICATION DEVICES
In addition to atmospheric control devices, which
help automate the temperature and humidity in
the garden, growers who wish to take pathogen
prevention one step further can implement a stand-
alone air purifi cation device. When combined with
an air intake fi lter and an atmospheric control sys-
tem, a stand-alone air purifi cation device can give
even more protection against pathogenic fungi to
an indoor garden or greenhouse crop. Essentially,
these devices have an internal fan that circulates
the air within the grow space; purifying the air in
the process. The technology used in these devices
can differ, but, most commonly, they either gener-
ate negative ions or utilize some sort of UV lighting.
Some of the UV lighting systems will actually pro-
duce ozone in the purifi cation process. Devices that
produce a detectable amount of ozone can cause
the ozone levels to build up in the grow space. This
can damage essential oil production or, in extreme
cases, become harmful to the gardener. Both the
size of the grow room and the amount of detectable
ozone should be carefully considered to ensure the
air purifi cation unit will be safe for the particular
garden application.
Perhaps the biggest draw to indoor and greenhouse
gardening is the heightened level of control over
the environment. That being said, a grower who
fails to control his or her garden’s climate prop-
erly will likely have a continuous battle with pest
insects and/or fungi pathogens. Ideally, a garden’s
temperature (and temperature variances) would be
controlled by an atmospheric controller. When the
temperature of an indoor garden or greenhouse is
automated, it makes it that much easier to control
the relative humidity. However, it must be remem-
bered that, plants are made mostly of water and
go through a natural transpiration process as they
grow. In other words, the plants themselves natu-
rally increase the humidity level in an enclosed area
as they grow.
Without proper air movement in the grow space,
the humidity levels close to the plants will be
much higher than the ambient air. For atmospheric
equipment to operate effi ciently and effectively,
the humidity of the room must be uniform. This
is why an ordinary oscillating fan is such a crucial
piece of equipment. If the ventilation system or air
conditioning unit cannot, on its own, handle the
increased humidity produced by the plants, a dehu-
midifi er should be implemented to keep the humid-
ity levels uniform. When humidity levels are kept
in check, pathogenic fungi cannot establish. This is
why the ultimate prevention and protection against
these pathogens is humidity control. Horticulturists
who prioritize uniform humidity levels and automate
control over the garden’s temperature and humidity
will be better equipped to prevent pathogenic fungi,
such as powdery mildew and botrytis. GG
Eric Hopper resides in Michigan’s beautiful Upper Peninsula
where he enjoys gardening and pursuing sustainability. He is
a Garden & Greenhouse senior editor and can be contacted
at [email protected].
26
www.GardenandGreenhouse.net
July 2019