this is from "mamedicinal " on breedbay i respect her work . this is the basis for my thinnking . then user mavrik has testing to back up early havest ...
Every now and then I read in the forums that you can get high CBD by a late harvest when the majority of the trichs are amber, but the more I look into it the more I think it's the other way round, that to get more CBD it's better to harvest early.
A while ago I found an interesting article (dated 1994) which discusses the variable amounts of CBD versus THC in the same variety, depending on where it is grown and the climate/environment.
Here's the link:
http://mojo.calyx.net/~olsen/HEMP/IHA/iha01201.html
Quote:
THC is thought to be produced by the plant.. from cannabidiol (CBD) which, in turn, is derived from cannabigerol (CBG) generated from non-cannabinoid precursors .. CBG is also the biogenetic precursor of cannabichromene (CBC). Some of the cannabinoids (e.g., cannabielsoin, cannabinol, and cannabicyclol) are probably degradation products of the enzymatically produced cannabinoids (e.g., CBD, THC and CBC, respectively).
Altho many people state that CBD increases along with CBN as the flowers get more mature and the trichomes become amber and that it forms as some of the THC breaks down, CBD is not mentioned as a degradation product in this article. It suggests that CBD is built by enzymatic processes, and not formed as THC breaks down. So this suggests that higher CBD can be obtained from an early harvest rather than a late one.
Actually, this ties in with another fact about CBD - it is NOT psycho-active. I take this to mean that it won't have you high flying around the ceiling or body stoned.
Many people comment that harvesting early means not enough buzz even tho the trichomes are brilliant clear white. This could mean that there are still high amounts of CBD in the resin possibly? And CBD has the effect of modulating the euphoric effects of THC, which could be another reason why early harvest reduces the highs if there is still an abundance of CBD in the herb.
Quote:
THC is a viscous hydrophobic oil (Garrett and Hunt 1974) that resists crystallization (Gaoni and Mechoulam 1971) and is of low volatility (Adams et al. 1941). Since the sticky resins produced and exuded on the surface of the plant are varying combinations of THC, other cannabinoids and a variety of terpenes, they can be seen as analogous to the waxy coatings of the cacti and other succulents that serve as a barrier to water loss in dry environments.
Bouquet (1950) has mentioned that the western side of Lebanon's mountainous Cannabis growing areas is less favorable for resin production because of humid sea winds..
Paris et al. (1975a) have demonstrated a marked increase in the cannabinoid content of Cannabis pollen with decreased humidity. Murari et al. (1983) grew a range of Cannabis fiber cultivars in three climatic zones of Italy and found higher THC levels in those plants grown in the drier "continental" (versus "maritime") climate. Hakim et al. (1986) report that CBD-rich English Cannabis devoid of THC produced significant amounts of THC and less CBD, when grown in the Sudan. This trend was accentuated in their next generation of plants.
This point is very interesting! Growing conditions in the UK or temperate regions seems to favour CBD content more than THC content in a variety which has significant amounts of THC but low CBD if grown in dry/hot climates.
Quote:
A preliminary investigation (Pate 1983) indicated that, in areas of high ultraviolet radiation exposure, the UV-B (280-315 nm) absorption properties of THC may have conferred an evolutionary advantage to Cannabis capable of greater production of this compound from biogenetic precursor CBD. The extent to which this production is also influenced by environmental UV-B induced stress has been experimentally determined by Lydon et al. (1987). Their experiments demonstrate that under conditions of high UV-B exposure, drug-type Cannabis produces significantly greater quantities of THC. They have also demonstrated the chemical lability of CBD upon exposure to UV-B (Lydon and Teramura 1987), in contrast to the stability of THC and CBC. However, studies by Brenneisen (1984) have shown only a minor difference in UV-B absorption between THC and CBD, and the absorptive properties of CBC proved considerably greater than either. Perhaps the relationship between the cannabinoids and UV-B is not so direct as first supposed. Two other explanations must now be considered. Even if CBD absorbs on par with THC, in areas of high ambient UV-B, the former compound may be more rapidly degraded. This could lower the availability of CBD present or render it the less energetically efficient compound to produce by the plant.
I think this means that conditions of high UV-B favours the production of THC but not CBD (which is unstable in high UV-B) and this in turn suggests that CBD is being converted to THC in the presence UV-B.
Quote:
..it has been noted.. that some tropical drug strains of Cannabis do not contain any CBD at all, yet have an abundance of THC.. The reverse seemed true as well. Seed from Mexican material devoid of CBD was planted in Mississippi and produced plants containing CBD..
..radioisotope tracer studies (Shoyama et al. 1975) have uncovered the intriguing fact that radiolabeled CBG (cannabigerol) fed to a very low THC-producing strain of Cannabis is found as CBD, but when fed to high THC-producing plants, appeared only as CBC and THC. Labeled CBD fed to a Mexican example of these latter plants likewise appeared as THC.
So, it appears that a high THC variety in a hot climate makes THC out of CBG and CBD, but a low THC variety will only make CBD out of CBG. I guess this means that if you live in a hot climate and you want high CBD you'll have to go for low THC varieties. OTOH if you live in temperate regions you can still get good levels of CBD from many varieties by conditions which reduce the development of THC - higher humidity, lower light levels (particularly of UV-B) and generally less stress on the plants in competing for moisture or nutrients.
I haven't found any research info to support high amounts of CBD in late harvesting, but I think this is an important issue for people who want to maximize CBD levels for medicinal reasons. I wish I could find more info on this, to either confirm an early harvest, or to show some other facts.
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@stowandgrow for real life cbd havest windows as well