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Handbook of Cannabis Production in Controlled Environments
Youbin Zheng, Youbin Zheng
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eBook - ePub
Handbook of Cannabis Production in Controlled Environments
Youbin Zheng, Youbin Zheng
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About This Book
For thousands of years, Cannabis sativa, commonly called cannabis or marijuana, has been used for many different purposes. Due to its enormous medicinal values, increasing numbers of countries and regions have started to legalise the cultivation of this plant. When grown commercially, cannabis is most often produced in controlled environments including greenhouse and indoor growing rooms, to ensure consistent growth and high quality. Even for field production, propagation is frequently conducted in controlled environments. Commercial operations and individual growers who cultivate cannabis for personal consumption, require scientific information on how to cultivate cannabis most effectively and efficiently. To meet these needs, scientists have been conducting research on how to optimize cannabis cultivation both in small and large scales.
Handbook of Cannabis Production in Controlled Environments is the result of collaborations between some leading cannabis scientists and highly experienced practitioners. Featuring full-color illustrations and photographs throughout, this book covers a broad range of topics include cannabis biology; science and techniques for breeding and propagation; management and optimization of both aerial and rootzone environments; plant nutrition and nutrient disorder diagnosis; crop training and pest management; harvesting and post-harvest processing. Along with the basic aspects of controlled environment cannabis production, this book summarises developments in these areas that may challenge old beliefs and improve production.
Led by Editor, Youbin Zheng, President of the Canadian Society for Horticultural Science/La SociĂŠtĂŠ Canadienne de Science Horticole, this book is a practical guide for cultivators, consultants, and researchers; a reference for students; and an information source for individuals who grow cannabis for personal consumption.
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1 Introduction
DOI: 10.1201/9781003150442-1
CONTENTS
1.1 Cannabis sativa
1.1.1 History
1.1.2 Appearance and Sexual Reproduction
1.1.3 Phytochemical Constituents
1.1.4 Origin and Classification
1.2 Why Controlled Environment Production
1.3 The Organization of This Book
Bibliography
1.1 CANNABIS SATIVA
Cannabis has been a dominant concern of society for several decades, and so most people have acquired appreciable knowledge (and some misunderstandings) of the subject. This book deals with technical aspects of commercial horticultural production in controlled environment facilities. Many unfamiliar with the phrase âcontrolled environmentâ may think of hospitals or airplanes, where certain environmental factors are controlled for the comfort and health of people. In the context of this book, the phrase denotes control of environmental factors that influence quality, yield and efficiency of plant production. âControlled environmentâ here can include growing facilities such as indoor growth rooms, greenhouses and high tunnels. The individual chapters, prepared by specialists, often assume that the reader is acquainted with some of the following background information.
1.1.1 HISTORY
The species Cannabis sativa has been grown as a field crop for thousands of years. Until the 20th century, Western countries cultivated it for fiber (called âhempâ) from the stem and edible seeds (called hempseed), while many Asian and African countries predominantly grew the plant for drug (âmarijuana,â âcannabisâ hereafter) usage. In the 20th century, concern about recreational usage led to prohibition in most of the Western world. This was followed by the development of a huge illicit drug trade and an associated black market which to this day supplies most cannabis consumption. In the 1990s, the medical use of cannabis was accepted in some nations, and subsequently also its recreational use, but governments insisted that the plants be cultivated in very secure indoor facilities, not outdoors. During the prohibition period, amateur breeders had selected high-yielding, early-maturing cannabis varieties ideally suited to indoor growth in basements and garages. These provided foundational material for the establishment of controlled environment cannabis facilities, which now represent multi-billionâdollar businesses in several countries. Today, cannabis production advice is available from innumerable âgray marketâ (unauthorized, but not significantly prosecuted) sources, from advisory booklets, online instructions, mail-order seed companies and horticultural equipment supply sources. However, while the roots of the cannabis industry trace to knowledge and strains developed clandestinely by amateurs, the scale and quality requirements of modern operations necessitate professional scientific and technological inputs. Indeed, in recent years, there have been many significant advances. This book reviews the science and technology that govern efficient controlled environment cultivation of cannabis.
1.1.2 APPEARANCE AND SEXUAL REPRODUCTION
Cannabis sativa is an annual, although some female plants can be maintained for more than a year under controlled environment conditions. Male and female plants cannot be reliably distinguished by appearance until they mature sufficiently to produce flowers. At the flowering stage, males are usually taller (typically 10â15%) but tend to be more delicate than the relatively robust females, and die after they have shed their pollen. The species is usually described as an herb, although the stems can become quite woody. The distinctive leaves with several palmately arranged leaflets (Figure 1.1) are so well known that C. sativa is probably the most widely recognized plant in the entire world. In both sexes, most of the flowers are in clusters. Typical of wind-pollinated plants, the flowers are quite small (just a few millimeters long) but very numerous, and lack big colorful petals or perfume that would attract insect pollinators. The male flower clusters are quite feathery, and take on a yellowish hue from the pollen within the five stamens of the male flowers (Figure 1.2 right). The female flowers are scarcely recognizable as flowers, consisting of a tiny ovary, enveloped by a tiny bract (elementary leaf) with protruding whitish stigmas (the pollen-receptive parts of flowers), giving the cluster of female flowers the appearance of being covered by whitish hairs (Figure 1.2 left). A female flower will mature into a single seed if pollinated (Figure 1.3)
The species is remarkably polymorphic (i.e., has many appearances), the result of evolution (natural selection) in nature, domestication (artificial selection of useful varieties), and considerable plasticity (i.e., different responses to growth conditions). Plants grown for fiber (always outdoors) are tall (typically 2 m or more) and have limited branching. Plants grown for oilseed (also always outdoors) may resemble fiber plants, but recent varieties have been bred to be quite short (sometimes about 1 m or less) and relatively unbranched. Wild plants (mostly âweedsâ) in hostile conditions (outdoors, of course) may be much shorter than 1 m and unbranched, but in good conditions some develop into highly branched giants sometimes exceeding 3 m. Wild plants are virtually always dioecious (with separate male and female plants), and until the latter half of the 20th century, so were fiber and oilseed varieties, but in recent times, many monoecious varieties (with male and female flowers on the same plant) have been bred.
FIGURE 1.1 Leaf of Cannabis sativa.
Source: Photo (public domain) by Christopher Thomas
FIGURE 1.2 Cannabis plants with female flowers (left) and male flowers (right).
Source: Photos by Youbin Zheng
FIGURE 1.3 Dried cannabis inflorescence and achenes (âseedsâ). Two seeds are particularly apparent at the bottom, close to the thumb.
Source: Photo by Youbin Zheng
In Asia, the homeland of cannabis drug production, the plants are traditionallyâand to this dayâcultivated outdoors. The varieties grown are âlandracesâ (a phrase denoting domesticated varieties selected locally by farmers, but more variable than modern cultivars created by modern breeders). In Chapter 3, the two principal kinds of cannabis landraces (âsativa-typeâ and âindica-typeâ) are discussed. The Asian cannabis plants are reproduced by seeds, and since they are dioecious, about half are male and half are female. Asian cannabis drug farmers long ago discovered that when pollen from the males fertilize the females so that they produce seeds, the quality of the females is much reduced. Moreover, the males are much inferior to the females as sources of drugs. The solution adopted was to rogue away (kill) the male plants as soon as they can be recognized (i.e., when they first produce male flowers). Black market growers who produce cannabis outdoors frequently follow this old practice. Well-cared for outdoor cannabis plants (provided with good soil, irrigation, a location open to the sun, and spaced at last 1 m apart) typically are well-branched and 2 m or more in height (Figure 1.4). They are impressive, but as explained in this book, their genetics and appearance are usually inappropriate for controlled environment production.
As noted previously, with prohibition of cannabis, much production shifted from field to indoors, and compact varieties (conventionally called âstrainsâ) were created. Although sexual reproduction played a large role in the hybridizations that led to the selection of numerous strains, propagation was found to be most easily accomplished by using stem cuttings (a form of vegetative reproduction) of female clones. Clones are simply genetically identical organisms, like identical twins, but with numerous copies. Clonal reproduction is well known in horticulture and agriculture (potato and apple varieties, for example, are clones). Commercial cannabis production in controlled environments is based mostly on female clones replicated by cuttings (with tissue culture increasingly supplementing cuttings). Clones are advantageous particularly because they produce very uniform plants, especially with regard to the feature or features that are valued. Nevertheless, growth conditions can significantly influence efficiency and quality of production, as documented in this book.
FIGURE 1.4 A Cannabis sativa plant about 3 m tall, grown in the authorâs garden in Ontario, Canada.
Source: Photo by Dr. Weiduo Si
All crops are basically systems for conversion of light into useful harvested materials, but in the case of cannabis, light also plays a special role because the maturation of most strains into females (also males, although they are usually not needed) is controlled by daily duration of uninterrupted dark period. Cannabis sativa is a âshort-dayâ plant, and in nature, shortening daylight (strictly, lengthening nights of uninterrupted darkness) initiates flowering. This is the key requirement in controlled environments for cannabis to flower (and produce cannabinoid-bearing buds) several times annually, whereas normally outdoor-grown plants can produce only one seasonal harvest. âDay-neutralâ or âautofloweringâ plants, as discussed in this book, are races that are indifferent to day length, which arose near the northern limits of survival of C. sativa, and are programmed to come into flower quickly to mature seeds before being killed by early winter. Autoflowering plants normally flower within 30â50 days after seeds germination, regardless of the day length. In theory, such plants (or their hybrids) could be advantageous, as they will mature rapidly under continuous light, but their usefulness remains to be demonstrated.
Commercial controlled environment cannabis production cycles are divided into three stages: propagation, vegetative growth and flowering. Each stage can have different lengths, depending on the genetics of the plants, the cultivation system and horticultural strategies. Many commercial growers employ soilless cultivation (with roots in nutrient solution or in solid soilless medium), but culture in natural soil is also practiced (See Chapter 5). Use of rooting stem cuttings is currently the most common propagation method used (see Chapter 4). Short stem cuttings are inserted in growing media and stimulated to produce roots. This is usually done under relatively low light, and takes about two weeks. The subsequent vegetative growth stage in short-day strains depends on whether natural light cycles only are employ...