View source for Cannabis sativa

{{SPlantbox
|familia=Cannabaceae
|genus=Cannabis
|species=sativa
|taxo_author=L.
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|width_ref=Plants for a Future
|poisonous=can be psychoactive
|lifespan=annual
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|water=moderate
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|image=Marijuana.jpg
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'''''Cannabis sativa''''' is an annual plant in the [[Cannabaceae]] family.  It is an [[herb]] that has been used throughout recorded history by humans as a source of fiber, for its seed oil, as food (see [[hemp]]), as a drug, as medicine, and for spiritual purposes. Each part of the plant is harvested differently, depending on the purpose of its use.

==Cultivation==
[[File:Cannabis sativa Koehler drawing.jpg|thumb|right|''Cannabis sativa'', scientific drawing from ''c''1900]]
The [[flower]]s of the female plant are arranged in [[raceme]]s and can produce hundreds of seeds. Male plants shed their pollen and die several weeks prior to seed ripening on the female plants. Although genetic factors dispose a plant to become male or female, environmental factors including the [[Day|diurnal]] light cycle can alter sexual expression.{{Citation needed|date=April 2008}} Naturally occurring [[monoecious]] plants, with both male and female parts, are either [[infertility|sterile]] or [[fertile]] but artificially induced "[[hermaphrodites]]" (a commonly used misnomer) can have fully functional reproductive organs. "Feminized" seed sold by many commercial seed suppliers are derived from artificially "hermaphrodytic" females that lack the male gene, or by treating the seeds with hormones or silver thiosulfate.

A ''Cannabis'' plant in the vegetative growth phase of its life requires more than 12–13 hours of light per day to stay vegetative. [[Flowering]] usually occurs when darkness equals at least 12 hours per day. The flowering cycle can last anywhere between five to ten weeks, depending on the strain and environmental conditions.

In soil, the optimum [[pH]] for the plant is 6.3 to 6.8. In [[hydroponics|hydroponic]] growing, the nutrient solution is best at 5.2 to 5.8, making ''Cannabis'' well-suited to hydroponics because this pH range is hostile to most bacteria and fungi.

* Cultivars primarily cultivated for their fiber, characterized by long [[Plant stem|stems]] and little branching.
* Cultivars grown for [[seed]] from which [[hemp oil]] is extracted.
* Cultivars grown for medicinal or recreational purposes. A nominal if not legal distinction is often made between industrial hemp, with concentrations of psychoactive compounds far too low to be useful for that purpose, and marijuana.

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Cannabis is very adaptable to soil and climatic conditions[269]. It prefers a rich loamy soil with plenty of humus[171] but it succeeds in ordinary garden soil[1] and also in calcareous soils[171]. When grown for fibre, it requires a mild temperate climate with at least 67cm annual rainfall, with abundant rain whilst the seeds are germinating and until young plants become established[269]. Cannabis thrives on rich, fertile, neutral to slightly alkaline, well-drained silt or clay loams with moisture retentive subsoils, it does not grow well on acid, sandy soils[269]. Of the many types of hemp, some are adapted to most vegetated terrains and climates[269]. Cannabis is reported to tolerate an annual precipitation range of 30 to 400cm, an average annual temperature range of 6 to 27°C and a pH in the range of 4.5 to 8.2[269]. Plants require little cultivation, except for weeding during early stages of growth. Hemp grows rapidly and soon crowds out weeds[269]. After the plants are 20 cm tall, weeding is abandoned. Hemp tends to exhaust the soil of nutrients, though some nutrients are returned to the soil after plants are harvested[269]. As Cannabis sativa has been cultivated for over 4,500 years for different purposes, many varieties and cultivars have been selected for specific purposes, as fibre, oil or narcotics. Drug-producing selections grow better and produce more drug in the tropics; oil and fibre producing plants thrive better in the temperate and subtropical areas. Many of the cultivars and varieties have been named as to the locality where it is grown mainly. However, all so called varieties freely interbreed and produce various combinations of the characters. The form of the plant and the yield of fibre from it vary according to climate and particular variety. Varieties cultivated particularly for their fibres have long stalks, branch very little, and yield only small quantities of seed. Varieties which are grown for the oil from their seed are short in height, mature early and produce large quantities of seed. Varieties grown for the drugs are short, much-branched with smaller dark-green leaves. Between these three main types of plants are numerous varieties which differ from the main one in height, extent of branching and other characteristics[269]. At least one variety has been selected for its virtually insignificant content of the narcotic principles[141]. This form is monoecious whereas most other forms are dioecious[141]. There is also said to be a tall Chinese form that has no narcotic effect[179]. Certain varieties do not form many side-shoots and these are the forms most commonly grown for their fibre[123]. Plants grown in warmer climates tend to be best for medicinal use, whilst those grown in more northerly latitudes produce the better fibre[4]. The seed is very attractive to birds and is often included in bird seed mixtures[7].

===Propagation===
Seed - sow in early spring in the greenhouse. When they are large enough to handle, prick the seedlings out into individual pots and plant them out into their permanent positions in early summer. Seeds germinate well at low temperatures, but not below 1°C[269]. The seed can also be sown outdoors in situ in mid spring.

===Pests and diseases===
A good companion plant for cabbages and other brassicas, it repels the cabbage white butterfly[4, 18, 20, 201] and also secretes a volatile essence from its roots that inhibits pathogenic micro-organisms in the soil[201].

==Varieties==
Subspecies:
*C. sativa L. subsp. sativa
*C. sativa L. subsp. indica

==Gallery==

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Image:Upload.png| photo 1
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==References==
<references/>
*http://www.pfaf.org/database/plants.php?Cannabis+sativa
<!--- xxxxx  *Flora: The Gardener's Bible, by Sean Hogan. Global Book Publishing, 2003. ISBN 0881925381  -->
<!--- xxxxx  *American Horticultural Society: A-Z Encyclopedia of Garden Plants, by Christopher Brickell, Judith D. Zuk. 1996. ISBN 0789419432  -->
<!--- xxxxx  *Sunset National Garden Book. Sunset Books, Inc., 1997. ISBN 0376038608  -->

==External links==
*{{wplink}}

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