Botany
See also: Cannabis
Cannabis belongs to the genus Cannabis in the family Cannabaceae and may include three species, Cannabis sativa, Cannabis indica, and Cannabis ruderalis, (APG II system) or one variable species.[1] It is typically a dioecious (each individual is either male or female) annual plant.[2][3][4]
C. sativa and C. indica generally grow tall, with some varieties reaching 4 metres, or 13 feet. Female plants produce tetrahydrocannabinol (THC) (up to 31% by weight) as the season changes from summer to autumn. C. ruderalis is very short, produces only trace amounts of THC, but is very rich in cannabidiol (CBD), which may be 40% of the cannabinoids in a plant and is an antagonist to THC, and it flowers independently of the photoperiod and according to age.[5] However, commercial cross-bred hybrids containing both ruderalis, indica and/or sativa genes exist (usually called autoflowering).
Cultivation requirements
Cannabis needs certain conditions to flourish.
Growth medium
Soil is required, except for cannabis grown with hydroponics or aeroponics
Sufficient nutrients—commercial potting soils usually indicate this as "N-P-K = x%-y%-z%" the percentages of the fundamental nutritional elements, i.e., nitrogen, phosphorus and potassium. Nutrients are often provided to the soil via fertilizers but such practice requires caution.
pH between 5.8 and 6.5. This value can be adjusted – see soil pH. Commercial fertilizers (even organic) tend to make the soil more acidic.
Warmth
The optimal day temperature range for cannabis is 24 to 30 °C (75 to 86 °F). Temperatures above 31 °C (88 °F) and below 15.5 °C (60 °F) seem to decrease THC potency and slow growth. At 13 °C (55 °F) the plant undergoes a mild shock, though some strains withstand frost temporarily.[6][7][8]
Light
Light can be natural (outdoor growing) or artificial (indoor growing).
Under artificial light, the plant typically remains under a regime of 16–24 hours of light and 0–8 hours of darkness from the germination until flowering, with longer light periods being conducive to vegetative growth, and longer dark periods being conducive to flowering. However, generally cannabis only requires thirteen hours of continuous light to remain in the vegetative stage.[9] The 'Gas Lantern Routine' is an alternate lighting schedule that has proven to be successful for growing cannabis, while saving a significant amount of energy.[10][11][12] For optimal health, cannabis plants require a period of light and a period of dark.[13] It has been suggested that, when subjected to a regimen of constant light without a dark period, cannabis begins to show signs of decreased photosynthetic response, lack of vigor, and an overall decrease in vascular development. Typically, flowering is induced by providing at least 12 hours per day of complete darkness. Flowering in cannabis is triggered by a hormonal reaction within the plant that is initiated by an increase in length of its dark cycle, i.e. the plant needs sufficient prolonged darkness for bract/bracteole [14] (flowering) to begin. Some Indica varieties require as little as 8 hours of dark to begin flowering, whereas some Sativa varieties require up to 13 hours.
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