Photosynthetic Photon Flux Density (PPFD) and Photoperiod: For vigorous
growth ofCannabisbiomass the optimum light quality, quantity and photoperiod is
very important. Light quality and quantity has a profound influence on photosyn-
thesis which ultimately affects the plant growth and development (Devlin 1975 ).
Cannabisin particular, is reported to be benefited from high PPFD for photosyn-
thesis and growth (Chandra et al. 2008 ). Different light sources can be used for
indoor propagation such as,fluorescent light bulbs (mainly for young cuttings),
metal halide bulbs, high pressure sodium lamps, induction bulbs and light emitting
diodes. To avoid overheating, a safe distance is maintained between bulbs and
plants. A photoperiod of eighteen hour or more is desirable for vegetative growth
whereas, 12 h photoperiod is recommended for the initiation offlowering.
Temperature: Temperature dependence of photosynthesis is reviewed by several
authors in different plant species (Sage and Sharkey 1987 ; Borjigidai et al. 2006 ;
Hikosaka et al. 2006 ; Nagai and Makino 2009 ). InCannabis, plant development
and growth of different varieties varies depending upon their original growth habitat
and the genetic makeup. Twentyfive to 30 °C growth temperature is however,
found to be optimum for most varieties ofCannabis(Chandra et al. 2008 ,2012a).
Irrigation and Relative Humidity: Humidity plays a critical role at every stage of
cannabisplant. In a close grow room environment, accumulation of humidity or
moisture is quite common due to irrigation and water evaporated by plants. Proper
ventilation, air circulation and sometimes dehumidification is required to maintain
optimum conditions. The amount of water and the frequency of watering of
Cannabisplants vary with the growth stage, size of the plants and containers,
growth temperature, humidity and many other factors.Cannabisrequires high
humidity at the juvenile (cutting or seedling) stage. Vegetative cuttings require a
regular water spray on the leaves to maintain a high humidity in its microclimate
until the plants are well rooted. Once established, top layer of soil must be allowed
to dry out before the plants are watered again. Humidity around 75% is recom-
mended during the juvenile stage and about 55–60% during the active vegetative
andflowering stages.
Air Circulation and Carbon dioxide in the Growing Room: Drier environment
and constant airflow in growing room prevent several diseases and mold formation
onCannabisplants. To circulate air around the plants, a steady fresh airflow from
outdoor ventilation and overhead revolving fans are recommended in indoor grow
room. A typical indoor cultivation under artificial lights is shown in Fig.3.6.An
enhancement in photosynthesis and plant growth under the elevated CO 2 concen-
tration is reported by several authors (Kimball 1983 ; Cure 1985 ; Cure and Acock
1986 ; Ceulemans et al. 1995 ; Idso and Idso, 1994 ). A close correlation between
photosynthesis and plant yield is reported by Zelitch ( 1975 ). Doubling in CO 2
concentration has been reported to increase the yield by 30% or more in many crops
(Poorter 1993 ). InC. sativa, doubling of CO 2 concentration (*750 ppm) was
reported to stimulate the rate of photosynthesis in different varieties by 38–48% as
compared to ambient CO 2 concentration (Chandra et al.2012b). Therefore, sup-
plementing CO 2 to the existing amount in the grow room during the light cycle is
recommended for vigorousCannabisgrowth.
3 Cannabis sativaL.: Botany and Horticulture 87