Professional Marijuana Grower May-June 2019 Issue | Page 26

FEATUREARTICLE
by Eric Hopper
The Light Cycle and How it Affects
Flower Initiation
T
he photoperiod is an extremely important aspect
of the flowering cycle in a cannabis garden. The
photoperiod is the duration of the light period
versus the dark period within a 24 hour cycle.
Generally speaking, cannabis is considered a short-day
plant, which means it will begin to flower as the amount
of light hours per day lessens (12 hours of light or less).
In nature, cannabis plants will begin to produce flowers
in the fall when the daylight hours become shorter. For
indoor gardeners or greenhouse growers using light
deprivation, a cannabis plant’s bloom cycle is initiated
by shortening the duration of the light cycle (and, thus,
increasing the duration of darkness).
When discussing horticultural lighting and photoperiods,
the focus is typically on how much light is being provided
to the garden. However, in order to encourage cannabis
plants to produce flowers, it is the duration of the dark
cycle that is of the utmost importance. It is the extended
dark period that actually triggers and maintains a can-
nabis plant’s hormones to produce flowers. Interruptions
in the dark cycle of an indoor garden (or greenhouse
with light deprivation) can cause a series of problems,
including reduced yields and hermaphroditic tendencies
(female plants that create male pollen, resulting in seed-
ed buds). To avoid issues that originate from an interrupt-
ed dark cycle, indoor horticulturists should strive to make
the dark cycle as “light-tight” or as dark as possible.
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26 • Professional Marijuana Grower
Generally speaking, 12 hours of darkness is enough to
trigger flowering in photosensitive plants, such as can-
nabis, and also to maintain healthy flower development.
However, many growers often underestimate the impor-
tance of how dark the dark cycle should be. In an ideal
situation, the garden’s dark cycle would be pitch-black.
Any light entering the flowering stage during the dark
cycle could potentially cause the plants to continue veg-
etative growth or, for dioecious plants, cause hermaph-
rodites to develop. When a cannabis plant is provided
with a dark period of 12 hours or more, it produces
specific hormones for the development of flowers. Inter-
ruptions in the dark cycle can hinder the development
of these flower-inducing hormones and, in some cases,
May/June 2019