shaggie-420
Well-Known Member
was trying to ad this to the How to but cant so ill place it here
this is a compilation of study's done on medical marijuana plants that i have been putting together
hope it is informative
Forget big colas and stinky buds: it's all about the resin.
Marijuana is perhaps the only plant in history grown primarily for its trichomes. Whether used for hashish or marijuana the objective is the same: production and harvest of THC-rich trichomes (crystals). Yet often the cultivator loses sight of the real goal of growing this plant. Bud size, density, coloration, flavor and odor are all of little value if they do not produce the euphoric sensations we seek.
Trichomes and resins
Trichomes come in many shapes and sizes and are used by plants for many different purposes. Cannabis uses its trichomes for a variety of purposes, some of which require THC and other cannabinoids to be effective, and others that do not.
The primary goal of any plant is to create and nurture seeds to the point where they will be viable for future growth. Trichomes help prevent seed damage from dessication, insects, animals, light degradation and fungal disease. Perhaps the most successful function of trichomes in the proliferation of cannabis is their attractiveness to humans. What better a creature to protect and spread a genus than the most advanced organism on the planet?
An important thing to remember is that heavy trichome production is not necessarily an indication of a potent plant. Some hemp strains have moderate layers of trichomes yet pack only a headache. In drug strains a dense stand of trichomes is a sign that it could be of high potency, but certainly not a guarantee.
This is because the resins that flow within may or may not hold the THC and other cannabinoids that we are looking for.
Indica varieties often look more heavily crystallized than Sativas, yet typically don't have the same mind-warp capabilities. Even with a known high-THC clone, THC level and cannabinoid ratios may change depending on environmental conditions.
What defines drug strain cannabis is the plant's ability to convert cannabidiol (CBD) or possibly cannabichromene (CBC) into THC.1 If we as growers do not provide the plant with reason to make this conversion it likely will devote its energy elsewhere, to aid in its survival.
Environmental Influence
It takes high quality genetics to produce high quality marijuana, but genetics is only half of the equation. The genetic structure (genotype) only plays 50% of the role in determining the appearance and quality (phenotype) of a given plant. The other half is determined by environmental conditions such as light, temperature, humidity and soil nutrition. All these factors play a role in both the physical and chemical nature of marijuana's trichomes.
The best way to take a look at how environment affects THC production is to look where on the planet cannabis has naturally adopted a high THC profile. As cannabis has spread around the world it has taken on many different traits to help in its adaptation to varied areas. The best drug varieties have always been found at equatorial or high altitude locations. The one thing which both of these variables have in common is high light intensity and a large amount of ultraviolet (UV) light in the spectrum.
Recent Swiss trials in outdoor plots of clones grown at different altitudes have shown that there is correlation between higher altitude and increased potency (although there seems to be a trade off in yield). This likely means that THC-rich resins act to protect the plant and its seed from both higher light intensities and ultraviolet presence. It's no surprise that cannabis has developed a chemical to protect itself against the Sun's damaging UV rays, as they can be injurious to all forms of life.
In a plant's search for survival, energy put towards unneeded processes is wasted energy. Therefore a high-THC plant grown in a low THC environment will likely produce a medium THC result.
Humidity also plays a role in plant resin production. Although some potent equatorial strains do seem to occur in high humidity areas, most high-test land races have evolved in drier areas, like Afghanistan. The aridity of the areas of Afghanistan where Indica strains have evolved is quite apparent by the trait of large dense flower clusters. This would only be an advantage in an area of low humidity, as flowers will mold in anything more.2
There are many examples of non-cannabis plants producing resins in order to protect themselves from drying out. The waxy coating on cacti and other succulent plants is a prime example.3 Marijuana flowered in humid conditions will often have a longer stalk on the glandular trichome than the same strain grown in drier conditions. While this may give the appearance of being very crystallized, it will likely contain less THC than the same plant grown in a drier environment. Another problem with longer trichome stalks is that the gland heads are more likely to break off during handling.
Flushing: pros and cons
Much time and thought has been put into the feeding needs of each part of marijuana's life cycle, yet for some reason the final stages of resin development always seem to be ignored. But the vegetative period of plant growth is only setting the platform for us to produce the trichomes that we are after.
Flushing in particular seems to be something that is over-emphasized by many of today's growers. Many growers "flush" their plants with straight water or clearing agents during the final weeks before harvest in an effort to improve taste and smokeability. The theory is that this forces the plant to use up stored nutrients that may affect these qualities. Although this is certainly true to some extent, what many are forgetting is that not all nutrients can be moved within the plant.
Nitrogen, which is the main factor in poor-tasting bud, can be moved within the plant. If not present in the root zone a plant will take it from the older leaves to support newer growth. Calcium, however, is a nutrient that cannot be moved within the plant, if it is not present in the root zone it is not available for growth. Little research has been done on nutritional requirements of cannabis during the final stages of flowering, but it seems likely that calcium is vital as it is crucial in cell division. A calcium deficiency at later stages could therefore adversely affect trichome production.
This is not as serious of a concern for soil-based growers, as lime or other calcium sources which are mixed into the soil likely will provide sufficient nutrition even while flushing with pure water. But hydroponic growers using very pure water sources with little naturally occurring calcium could have problems. Flushing is certainly a valid technique, but is easily overdone and is not a quick fix for overfeeding earlier in the flower stage.
Some studies have shown that high potassium levels have a negative influence on THC production,4 which would correlate to the general belief that while hemp crops uptake more potassium than phosphorous, the reverse seems to be true for drug and seed cannabis crops.2 A study on how to minimize THC levels in hemp crops showed that THC levels in newer leaf growth decreased as nitrogen levels were increased.5 As no THC measurement was taken from floral clusters we can only speculate that the same would likely hold true in buds. This would also explain the good results that most growers have flushing their plants, as nitrogen is the nutrient most easily flushed from the soil.
Companion planting
Much research is still needed on the interrelationships of plants in the garden. Little is known about common vegetable garden plants effect on each other, let alone how they may react with cannabis.
Growing certain plants in proximity to each other has been documented to cause noticeable effects on growth, both positive and negative. The main companion plant that has attracted interest with underground marijuana researchers is stinging nettle (Urtica dioica) which has been said to increase essential oils in many plants.6
Breeding for potency
Marijuana is unique from an evolutionary standpoint in being the only plant in history that in some cases has been grown and bred for over two decades under nothing but artificial light. It is very likely that there have already been some genetic changes that have taken place as a result of this. All plants, especially cannabis, will quickly adapt to a new habitat by adding or dropping traits over successive generations. With breeders doing potentially as many as three or four generations per year, over 20 years there is great opportunity for drift from original genotypes.
Some "oldtimers" of the cannabis community have theorized that the use of high pressure sodium (HPS) light as a sole source of lighting has resulted in unconscious selection for lower THC parents during breeding.7 This theory is based on the assumption that ultraviolet light is a large causal factor in the plants production of THC. As HPS lights produce little in the way of UV, the lower potency plants could look the most vigorous in early selections (before flowering) as they would have a genetic advantage over high THC plants (less wasted energy).
A common way of conducting a breeding program where space is limited is to start large seed lots and then select the best individuals for flowering. Vic High and others have done some preliminary research into creating high UV environments by adding tanning or medical UV lights to their regular lighting for early seedling selections.8 As most Dutch breeding is done behind closed doors it is unknown whether this is used by any breeders in Holland.
Tricks of the trade
Delving through the history of marijuana cultivation you will find a myriad of techniques used to supposedly increase THC production. Much of this is little more than hippie folklore, but over the years some techniques have appeared which seem based on some amount of science.
Although some of the younger growers these days may never have used a metal halide light, many of the older set still swear by them as a complement to high-pressure sodiums in the flower room. With the advent several years ago of the Son-Agro HPS bulbs and others like it, which offer a higher amount of blue in the spectrum than standard HPS, many growers have felt that that they can do away with metal halides altogether. Growing strictly under sodiums has its advantages in terms of yield per watt, but is still lacking as far as a balanced spectrum when compared to a mix of HPS and halide.
Anyone that has ever seen a mixed light garden can testify that the healthiest, most crystallized buds occur where the two spectrums overlap. Again this brings us back to the UV factor, as metal halide bulbs emit a fair amount of UV while HPS emit almost none. Most growers employing halides in conjunction with HPS do so at a 2:1 HPS:halide ratio. Many growers, especially those restricted to one light, have been having good success using one of the new enhanced metal halide bulbs such as Sunmaster, which have a more balanced spectrum than either sodium or regular halide alone.
Glass and plastic materials used in greenhouses and air/water cooled light reflectors will block most useful wavelengths of UV from reaching plants. Luckily, recent research has shown that allowing UV to enter the greenhouse has many advantages on non-cannabis crops, and so some European greenhouses are beginning to switch to UV transparent glazing materials. Trade names for some of these products are Planilux, Diamant or Optiwhite. Plastic made from polymethylmethacrylate (PMMA) also transmits UV-B (the type that we are looking for). Traditional greenhouse coverings such as polyvinyl chloride (PVC), fiberglass, polycarbonate or regular glass allow little if any UV-B transmission.9
Harvesting in the morning ensures that your plant will be at peak THC content, as cannabis has shown THC fluctuations peaking in morning and dropping during the day. Some growers leave their lights off for several days before harvest to increase potency. This seems to have some scientific validity as light has been shown to degrade THC, hence the morning peaks. As light is the degrading factor and the plant still has the ability to manufacture THC during darkness, leaving the lights off for a day or two before harvest likely utilizes the plants stored potential for THC conversion without any opportunity for it to be degraded into cannabinol (CBN) and other breakdown products.8
Traditionally marijuana has been harvested when the pistils die and the calyx starts to swell into a false seed pod. These days the best growers are getting much more detailed in their harvesting criteria. They take a close look at the trichomes themselves to judge peak harvest. Evidence that this is the only real way to tell peak maturity is in Sagarmatha's strain Matanuska Tundra, which ripens resin glands while most pistils are still alive and white. This seems an odd twist of evolution but proves that the pistil color and ripe glands do not necessarily have any correlation.
A small 25x or more pocket microscope, which can be picked up inexpensively at any electronic store, works well for taking a closer look at trichome development. What we are examining are the capitate stalked glandular trichomes, which will be a round gland head supported on a stalk. The coloration of these gland heads can vary between strains and maturity. Most strains start with clear or slightly amber heads which gradually become opaque when THC levels have peaked and are beginning to degrade. Regardless of the initial colour of the resin head, with careful observation you should be able to see a change in coloration as maturity levels off.
Some cultivators wait for about half of the heads to go opaque before harvest to ensure maximum THC levels in the bud. Of course nothing tells the truth more than your own head, so try samples at various stages to see what's right for you. While you may be increasing the total THC level in the bud by allowing half of the glands to go opaque, the bud will also have a larger proportion of THC breakdown products such as CBNs, which is why some people prefer to harvest earlier while most of the heads are still clear.
Indica varieties usually have a 1-2 week harvest window to work with, while Sativas and Indica/Sativa hybrids may have a much longer period to play with.
Glandular conclusion
With the growing popularity of personal hashmaking through precision screening, many growers are starting to pay closer attention to the development of glands. The use of different size screens to separate glands of different sizes can only broaden our knowledge of the subtle nuances of trichome quality.
Growers using the same clone line over many crops have an excellent opportunity to play with some of these different techniques, as the main variable will be the environment, not the plant. Keep in mind that different strains may react very differently to the same techniques so be careful about drawing general conclusions.
Marijuana growers must look closer at their crop than the average farmer to achieve a premium product. Rows upon rows of beautiful plants are of no use if they do not glisten with the THC-laden trichomes that are the object of our quest.
Nurture your trichomes and feed your head!
References:
1) Starks, Michael. 1977. Marijuana Chemistry Genetics, Processing and Potency. Ronin Publishing, Inc., Berkeley, CA pp. 17-86.
2) McParland, Clarke, Watson. Hemp Diseases and Pests; management and biological control, CABI Publishing, New York, NY
3) Pate, DW, 1994. Chemical ecology of Cannabis. Journal of the International Hemp Association 2: 29, 32-37.
4) Kutscheid, 1973. Quantitative variation in chemical constituents of marihuana from stands of naturalized Cannabis sativa L. in east central Illinois. Economic Botany 27: 193-203.
5) Bócsa, Máthé and Hangyel. Effect of nitrogen on tetrahydrocannabinol (THC) content in hemp leaves at different positions. 1997. Journal of the International Hemp Association 4(2): 78 -79.
6) Helen Philbrick and Richard B Gregg. Companion Plants and How to Use Them. 1996. Devin-Adair Company, Old Greenwich, CT.
7) Oldtimer1, 2001. Personal communication
8) Vic High, 2001. BC Growers Association. Web site and help desk.
9) Hoffman, Dr Silke. 2001. Ultraviolet radiation in the greenhouse. Floraculture International, May 2001. Ball Publishing, Batavia, Illinois. pp18-27.
- An excellent general reference is Marijuana Botany, by Robert Connell Clarke. Ronin Publishing, Inc. Berkeley, CA
this is a compilation of study's done on medical marijuana plants that i have been putting together
hope it is informative
Forget big colas and stinky buds: it's all about the resin.
Marijuana is perhaps the only plant in history grown primarily for its trichomes. Whether used for hashish or marijuana the objective is the same: production and harvest of THC-rich trichomes (crystals). Yet often the cultivator loses sight of the real goal of growing this plant. Bud size, density, coloration, flavor and odor are all of little value if they do not produce the euphoric sensations we seek.
Trichomes and resins
Trichomes come in many shapes and sizes and are used by plants for many different purposes. Cannabis uses its trichomes for a variety of purposes, some of which require THC and other cannabinoids to be effective, and others that do not.
The primary goal of any plant is to create and nurture seeds to the point where they will be viable for future growth. Trichomes help prevent seed damage from dessication, insects, animals, light degradation and fungal disease. Perhaps the most successful function of trichomes in the proliferation of cannabis is their attractiveness to humans. What better a creature to protect and spread a genus than the most advanced organism on the planet?
An important thing to remember is that heavy trichome production is not necessarily an indication of a potent plant. Some hemp strains have moderate layers of trichomes yet pack only a headache. In drug strains a dense stand of trichomes is a sign that it could be of high potency, but certainly not a guarantee.
This is because the resins that flow within may or may not hold the THC and other cannabinoids that we are looking for.
Indica varieties often look more heavily crystallized than Sativas, yet typically don't have the same mind-warp capabilities. Even with a known high-THC clone, THC level and cannabinoid ratios may change depending on environmental conditions.
What defines drug strain cannabis is the plant's ability to convert cannabidiol (CBD) or possibly cannabichromene (CBC) into THC.1 If we as growers do not provide the plant with reason to make this conversion it likely will devote its energy elsewhere, to aid in its survival.
Environmental Influence
It takes high quality genetics to produce high quality marijuana, but genetics is only half of the equation. The genetic structure (genotype) only plays 50% of the role in determining the appearance and quality (phenotype) of a given plant. The other half is determined by environmental conditions such as light, temperature, humidity and soil nutrition. All these factors play a role in both the physical and chemical nature of marijuana's trichomes.
The best way to take a look at how environment affects THC production is to look where on the planet cannabis has naturally adopted a high THC profile. As cannabis has spread around the world it has taken on many different traits to help in its adaptation to varied areas. The best drug varieties have always been found at equatorial or high altitude locations. The one thing which both of these variables have in common is high light intensity and a large amount of ultraviolet (UV) light in the spectrum.
Recent Swiss trials in outdoor plots of clones grown at different altitudes have shown that there is correlation between higher altitude and increased potency (although there seems to be a trade off in yield). This likely means that THC-rich resins act to protect the plant and its seed from both higher light intensities and ultraviolet presence. It's no surprise that cannabis has developed a chemical to protect itself against the Sun's damaging UV rays, as they can be injurious to all forms of life.
In a plant's search for survival, energy put towards unneeded processes is wasted energy. Therefore a high-THC plant grown in a low THC environment will likely produce a medium THC result.
Humidity also plays a role in plant resin production. Although some potent equatorial strains do seem to occur in high humidity areas, most high-test land races have evolved in drier areas, like Afghanistan. The aridity of the areas of Afghanistan where Indica strains have evolved is quite apparent by the trait of large dense flower clusters. This would only be an advantage in an area of low humidity, as flowers will mold in anything more.2
There are many examples of non-cannabis plants producing resins in order to protect themselves from drying out. The waxy coating on cacti and other succulent plants is a prime example.3 Marijuana flowered in humid conditions will often have a longer stalk on the glandular trichome than the same strain grown in drier conditions. While this may give the appearance of being very crystallized, it will likely contain less THC than the same plant grown in a drier environment. Another problem with longer trichome stalks is that the gland heads are more likely to break off during handling.
Flushing: pros and cons
Much time and thought has been put into the feeding needs of each part of marijuana's life cycle, yet for some reason the final stages of resin development always seem to be ignored. But the vegetative period of plant growth is only setting the platform for us to produce the trichomes that we are after.
Flushing in particular seems to be something that is over-emphasized by many of today's growers. Many growers "flush" their plants with straight water or clearing agents during the final weeks before harvest in an effort to improve taste and smokeability. The theory is that this forces the plant to use up stored nutrients that may affect these qualities. Although this is certainly true to some extent, what many are forgetting is that not all nutrients can be moved within the plant.
Nitrogen, which is the main factor in poor-tasting bud, can be moved within the plant. If not present in the root zone a plant will take it from the older leaves to support newer growth. Calcium, however, is a nutrient that cannot be moved within the plant, if it is not present in the root zone it is not available for growth. Little research has been done on nutritional requirements of cannabis during the final stages of flowering, but it seems likely that calcium is vital as it is crucial in cell division. A calcium deficiency at later stages could therefore adversely affect trichome production.
This is not as serious of a concern for soil-based growers, as lime or other calcium sources which are mixed into the soil likely will provide sufficient nutrition even while flushing with pure water. But hydroponic growers using very pure water sources with little naturally occurring calcium could have problems. Flushing is certainly a valid technique, but is easily overdone and is not a quick fix for overfeeding earlier in the flower stage.
Some studies have shown that high potassium levels have a negative influence on THC production,4 which would correlate to the general belief that while hemp crops uptake more potassium than phosphorous, the reverse seems to be true for drug and seed cannabis crops.2 A study on how to minimize THC levels in hemp crops showed that THC levels in newer leaf growth decreased as nitrogen levels were increased.5 As no THC measurement was taken from floral clusters we can only speculate that the same would likely hold true in buds. This would also explain the good results that most growers have flushing their plants, as nitrogen is the nutrient most easily flushed from the soil.
Companion planting
Much research is still needed on the interrelationships of plants in the garden. Little is known about common vegetable garden plants effect on each other, let alone how they may react with cannabis.
Growing certain plants in proximity to each other has been documented to cause noticeable effects on growth, both positive and negative. The main companion plant that has attracted interest with underground marijuana researchers is stinging nettle (Urtica dioica) which has been said to increase essential oils in many plants.6
Breeding for potency
Marijuana is unique from an evolutionary standpoint in being the only plant in history that in some cases has been grown and bred for over two decades under nothing but artificial light. It is very likely that there have already been some genetic changes that have taken place as a result of this. All plants, especially cannabis, will quickly adapt to a new habitat by adding or dropping traits over successive generations. With breeders doing potentially as many as three or four generations per year, over 20 years there is great opportunity for drift from original genotypes.
Some "oldtimers" of the cannabis community have theorized that the use of high pressure sodium (HPS) light as a sole source of lighting has resulted in unconscious selection for lower THC parents during breeding.7 This theory is based on the assumption that ultraviolet light is a large causal factor in the plants production of THC. As HPS lights produce little in the way of UV, the lower potency plants could look the most vigorous in early selections (before flowering) as they would have a genetic advantage over high THC plants (less wasted energy).
A common way of conducting a breeding program where space is limited is to start large seed lots and then select the best individuals for flowering. Vic High and others have done some preliminary research into creating high UV environments by adding tanning or medical UV lights to their regular lighting for early seedling selections.8 As most Dutch breeding is done behind closed doors it is unknown whether this is used by any breeders in Holland.
Tricks of the trade
Delving through the history of marijuana cultivation you will find a myriad of techniques used to supposedly increase THC production. Much of this is little more than hippie folklore, but over the years some techniques have appeared which seem based on some amount of science.
Although some of the younger growers these days may never have used a metal halide light, many of the older set still swear by them as a complement to high-pressure sodiums in the flower room. With the advent several years ago of the Son-Agro HPS bulbs and others like it, which offer a higher amount of blue in the spectrum than standard HPS, many growers have felt that that they can do away with metal halides altogether. Growing strictly under sodiums has its advantages in terms of yield per watt, but is still lacking as far as a balanced spectrum when compared to a mix of HPS and halide.
Anyone that has ever seen a mixed light garden can testify that the healthiest, most crystallized buds occur where the two spectrums overlap. Again this brings us back to the UV factor, as metal halide bulbs emit a fair amount of UV while HPS emit almost none. Most growers employing halides in conjunction with HPS do so at a 2:1 HPS:halide ratio. Many growers, especially those restricted to one light, have been having good success using one of the new enhanced metal halide bulbs such as Sunmaster, which have a more balanced spectrum than either sodium or regular halide alone.
Glass and plastic materials used in greenhouses and air/water cooled light reflectors will block most useful wavelengths of UV from reaching plants. Luckily, recent research has shown that allowing UV to enter the greenhouse has many advantages on non-cannabis crops, and so some European greenhouses are beginning to switch to UV transparent glazing materials. Trade names for some of these products are Planilux, Diamant or Optiwhite. Plastic made from polymethylmethacrylate (PMMA) also transmits UV-B (the type that we are looking for). Traditional greenhouse coverings such as polyvinyl chloride (PVC), fiberglass, polycarbonate or regular glass allow little if any UV-B transmission.9
Harvesting in the morning ensures that your plant will be at peak THC content, as cannabis has shown THC fluctuations peaking in morning and dropping during the day. Some growers leave their lights off for several days before harvest to increase potency. This seems to have some scientific validity as light has been shown to degrade THC, hence the morning peaks. As light is the degrading factor and the plant still has the ability to manufacture THC during darkness, leaving the lights off for a day or two before harvest likely utilizes the plants stored potential for THC conversion without any opportunity for it to be degraded into cannabinol (CBN) and other breakdown products.8
Traditionally marijuana has been harvested when the pistils die and the calyx starts to swell into a false seed pod. These days the best growers are getting much more detailed in their harvesting criteria. They take a close look at the trichomes themselves to judge peak harvest. Evidence that this is the only real way to tell peak maturity is in Sagarmatha's strain Matanuska Tundra, which ripens resin glands while most pistils are still alive and white. This seems an odd twist of evolution but proves that the pistil color and ripe glands do not necessarily have any correlation.
A small 25x or more pocket microscope, which can be picked up inexpensively at any electronic store, works well for taking a closer look at trichome development. What we are examining are the capitate stalked glandular trichomes, which will be a round gland head supported on a stalk. The coloration of these gland heads can vary between strains and maturity. Most strains start with clear or slightly amber heads which gradually become opaque when THC levels have peaked and are beginning to degrade. Regardless of the initial colour of the resin head, with careful observation you should be able to see a change in coloration as maturity levels off.
Some cultivators wait for about half of the heads to go opaque before harvest to ensure maximum THC levels in the bud. Of course nothing tells the truth more than your own head, so try samples at various stages to see what's right for you. While you may be increasing the total THC level in the bud by allowing half of the glands to go opaque, the bud will also have a larger proportion of THC breakdown products such as CBNs, which is why some people prefer to harvest earlier while most of the heads are still clear.
Indica varieties usually have a 1-2 week harvest window to work with, while Sativas and Indica/Sativa hybrids may have a much longer period to play with.
Glandular conclusion
With the growing popularity of personal hashmaking through precision screening, many growers are starting to pay closer attention to the development of glands. The use of different size screens to separate glands of different sizes can only broaden our knowledge of the subtle nuances of trichome quality.
Growers using the same clone line over many crops have an excellent opportunity to play with some of these different techniques, as the main variable will be the environment, not the plant. Keep in mind that different strains may react very differently to the same techniques so be careful about drawing general conclusions.
Marijuana growers must look closer at their crop than the average farmer to achieve a premium product. Rows upon rows of beautiful plants are of no use if they do not glisten with the THC-laden trichomes that are the object of our quest.
Nurture your trichomes and feed your head!
References:
1) Starks, Michael. 1977. Marijuana Chemistry Genetics, Processing and Potency. Ronin Publishing, Inc., Berkeley, CA pp. 17-86.
2) McParland, Clarke, Watson. Hemp Diseases and Pests; management and biological control, CABI Publishing, New York, NY
3) Pate, DW, 1994. Chemical ecology of Cannabis. Journal of the International Hemp Association 2: 29, 32-37.
4) Kutscheid, 1973. Quantitative variation in chemical constituents of marihuana from stands of naturalized Cannabis sativa L. in east central Illinois. Economic Botany 27: 193-203.
5) Bócsa, Máthé and Hangyel. Effect of nitrogen on tetrahydrocannabinol (THC) content in hemp leaves at different positions. 1997. Journal of the International Hemp Association 4(2): 78 -79.
6) Helen Philbrick and Richard B Gregg. Companion Plants and How to Use Them. 1996. Devin-Adair Company, Old Greenwich, CT.
7) Oldtimer1, 2001. Personal communication
8) Vic High, 2001. BC Growers Association. Web site and help desk.
9) Hoffman, Dr Silke. 2001. Ultraviolet radiation in the greenhouse. Floraculture International, May 2001. Ball Publishing, Batavia, Illinois. pp18-27.
- An excellent general reference is Marijuana Botany, by Robert Connell Clarke. Ronin Publishing, Inc. Berkeley, CA
