Taken from CC magazine spring 2008 issue.
The colors of cannabis are a highly debated subject with different schools of thought prevailing as to why cannabis displays different hues. Many growers feel that reds, pinks, and purples indicate a stronger, more potent bud(some think the opposite) ; others feel that the sight of any other color than green indicates the plants were grown in a cold climate. Cooler temperature is just one factor in the color of your bud, and while purple bud can be amazingly potent, you'll be sure to find green bud thats just as amazingly so. Long time growers can attest to the exceptional variety of colors attainable in your everyday marijuana crop.
An annual plant, cannabis completes its life cycle within one year, starting as a seed, then germinating, maturing, reproducing, and dying. For a large part of its life, cannabis is green, the color the result of Chlorophyll, a plant chemical significant to the plant's photosynthesis ability. During the vegetative stage of its life, cannabis will be a shade of green that can be used as a health indicator of the plant.
A healthy plant exudes a vibrant green luster, whereas leaves and stems suffering from nutrient deficiencies change from green to various other colors. Nitrogen deficient plants produce yellow leaves , a sign of diminished chlorophyll production. Plants lacking phosphorus produce small, dark green leaves, with purple veins, purple leaf stems, and purple streaked stocks. When a plant lacks potassium, the leaves turn yellow, then brown, and eventually die. Deficiencies in zinc, magnesium and calcium all cause color changes.
While color changes in plants can indicate the state of deficiencies, color change can also occur in healthy vigorous marijuana plants. Color differences in the leaves of healthy plants are a result of genetic and environmental influences, and also occur as plants near the end of their life cycle. Pistil color changes are influenced by the grow medium's PH effect on the fragile cannabis flower. The beautiful green of the cannabis plant wasn't the only color present during the vegetative stage, but until the lengthening dark cycle triggers the plant to stop the production of the green chlorophylls, we can't begin to see the yellow and gold color of the carotenoids. Its perfectly natural for cannabis leaves to change colors and die off as the plants reach their "autumn" or finishing stage, showing varying shades of green, yellow gold and many more.
Some plants will turn red and purple as anthocyanins are produced using excess sugars in the leaves and spreading through cell fluids. The PH of the cell fluid determines the color variation, with an acidic fluid producing reddish hues, and an alkiline fluid producing blues. Cellular PH being genetically regulated, each strain has its own unique combinations of chlorophyll and carotenoids and potential for anthocyanins production, giving a great splash of color to a diversified grow as nights grow longer and and temperature cools. Many strain's color range is limited exclusively to greens and yellows through the life cycle.
In addition to the autumnal color changes in the leaves, many species show colors in their stems when finished in cooler temperatures. Some, like Blackberry from V.I.S.C. and blueberry, have colored buds in all but the warmest grows; the colors of these buds can change intensity and even hues when subjected to colder nights. While these colors are caused by the same plant components as in the leaves, there is the genetic roll of the die here. Black a V.I.S.C. original is a phenotype whose bud is always a dark purple in any temperature grow, yet Black hybrids will grow in colors ranging from purple to mauve to white. The purple color seems dependent on recieving a recessive gene from both parents, which allows for greater glucose conversion into anthocyanins, and having a suitable cellular PH. Not related to size or to resin production, bud color is purely aesthetic in value.
While small and slight, the pistil(reproductive flower) of the female cannabis plant can have an impact far greater than its size on your overall impression of the plant. Fucking Incredible by V.I.S.C. is a plant whose pistils can change colors. Certain nutrient formulations with a PH level of 6.8 cause F.I. to produce budes with reddish pink or even magents pistills, while thee same plant grown in a lower PH will develop white pistils.
Marijuana plants are not the only examples of flowers that can react to the PH of their medium. The hydrangea(hydrangea macrophylla) has flowers that change colors- pink in alkaline and blue in acidic. This is a great example of interplaying environmental and genetic influences. While all strains are effected by adjusting the ph of the soil, the few that exhibit coloured pistils as a result are a visual joy in your grow.
It is genetically believed that the PH of a plant's cells is genetically regulated and not influenced by the growing mediums PH, and the change of colors can be explained by the plants ability to absorb certain elements only in suitable PH soil. In the case of the hydrangea flower , the blue color is the result of the plants intake of aluminum, something most garden soils contain, which will not be useable by the hydrangea in alkaline soil.
I have witnessed the amazing array of colors naturally available in this fantastic plant for decades, and am continually amazed by the diversity. I have also seen growers "creating" gold coloured weed by starving their plants, and others trying to change colors of the bud by watering with kool-aid.
As a longtime breeder of cannabis, I am not a scientist and haven't tried to bring an exhaustive understanding of the biology of plants to this forum. I have, however, brought forward a number of factors and possible influences relating to the variety of colors in cannabis. Genetics, maturity, PH, amount of light, temperature, and even available sugars can influence the colors of cannabis. Some of these factors are easily controlled, others seemingly impossible; with knowledge comes ability.
Growing a variety of species in your garden is immensely rewarding in many ways, to which color can be a spectacular addition. While color will not change the plants potency or yields, it is possible to enhance the many colors in your garden, naturally enhancing its beauty and the enjoyment of the diversity that cannabis gives us. For me, marijuana is a beautiful species that I will always grow and enjoy, in more ways than one.
