Nutrient solution temperature can build up
surprisingly fast and become excessive under hot lights
and in systems with limited root zones. Research shows
that even a short duration of root zone heat buildup
can have harsh effects that cannot be compensated
by having a low daily temperature average. Just a few
minutes a day of root zone temperatures above 86°F
can retard the growth of some heat-sensitive crops like
lettuce and parsley.
While regular checks ensure roots don’t get cooked,
growers can more actively manipulate root zone
temperatures to fool many plants into handling higher-
than-optimal air temperatures. Root zone chilling is a
well-known technique used by many commercial growers
in warm or tropical climates for cool-season crops like
butterhead lettuce, herbs, and other vegetables. Research
shows chilling the nutrient solution down to as low as
61-64°F allows these crops to grow and produce well at
ambient air temperatures of 82-97°F, which are above
optimal. Other researchers report that chilling the nutrient
solution of lettuce crops reduces the occurrence of the
fungal root disease Pythium aphanidermatum. Without
chilling, the root zone could warm up to the level of the
air, creating numerous problems like slow growth, lack
of heart formation, bolting, tip burn, and low marketable
yields. However, trials show that root zone chilling must
be applied soon after early crop establishment and
maintained for the life of the crop for maximum effect.
Root zone temperature strongly affects shoot growth
and other plant processes.
There are many different approaches to
manipulating root zones to influence plant
physiology. And while techniques like increasing
the EC to boost tomato flavor and controlling
the temperature of the root zone to prevent
bolting in lettuce are well-known, researchers
are continually developing new methods for
wider range of indoor hydroponic crops.
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