i came across this while googling...
"Other than green, purple is the most common color in living marijuana. Triggered by seasonal temperature changes (just as trees change color in the fall), the vibrant hues of the mature pot plant are also the result of genetics and the creativity of the cultivator or breeder.
Indoors and outdoors, color can be influenced by deficiencies as well as by temperature. The intense green of chlorophyll usually overpowers other colors, such as red, orange and the coveted purple. Chlorophyll tends to break down late in the season, and a pigment known as anthocyanin is unmasked and allowed to show through.
For purple color to develop upon maturation, a strain must have the genetic potential to produce anthocyanin pigments. However, the color might never be shown if environmental conditions dont cause chlorophyll breakdown. Colombian and Hindu Kush strains tend to develop purple coloration when subjected to low night temperatures during the end of their life cycles. Purple Orangutan, originally from Afghanistan with heavy traits of the Hindu Kush, produces some of the darkest purple and blue tones found in any marijuana strain.
Another pigment called carotenoid is largely responsible for the yellow, orange, red and brown colors of marijuana. These colors begin to show in the leaves and calyxes of certain strains as the green chlorophyll color fades. Gold strains reveal underlying yellow and orange pigments as they mature. Red strains are usually closer to reddish brown in color, though certain carotenoid and anthocyanin pigments are nearly red, and streaks of these colors occasionally appear in the petioles (the slender stems supporting the leaflets) in ripe flowers. The red color in pressed, low-grade tops often consists of masses of reddish-brown dried pistils."
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We then scome across an interesting and undertested product proven to turn buds purple...
PURPLE MAXX
This product has been in development for over 2 years under the name of STACKER. We discovered a combination of organic compounds that would encourage plants to stack their flowering sites closer together, increase resin production and flower size and stimulate extreme crystal development. Early this year we were optimizing a feeding regimen using GRAVITY and STACKER that would lead to even more extreme results when 2 of our beta testers out in the hills reported that STACKER caused their plants to turn dark purple! We decided to rename it PURPLE MAXX. Word spread like wildfire through the hills of Humboldt County and soon we were handing out 50-100 samples a week. Soon people were coming in asking for gallons! Please keep in mind: This is an experimental product that we dont think is ready for market but due to extreme demand we are releasing it in limited quantities.
DIRECTIONS:
No one should buy this product with the expectation that they will get a drastic color change with one or two applications. That only happens for about 1/4 to 1/3 of our testers when they foliar feed or water with PURPLE MAXX about 3 weeks before finish. Many people claim it doesnt cause any color change at all. The following directions are presently the latest refinement in the feeding schedule. This product usually causes a massive uptake of nutrients so fertilizer solution should be cut back by about 1/3 (750-900 ppm). (1) If you are close to the end of the flowering cycle it would be best to feed PURPLE MAXX with plain water. Use 1/2 to 1 tsp. of MAXX per gallon of water right up to the end. If you have good air circulation you can spray with 1/2 to 1 tsp/ gallon. Some testers have used a lot more. (2) If you are just starting the bloom cycle, use 1/2 to 1 tsp. per gallon of water and apply about once a week or foliar feed with 2 ml/ gallon (1 tsp/ 2 1/2 gallons of water). If plants show no sign of tip burn, nutrient strength can be increased somewhat. Regardless of color change, almost all testers over the past 2 years have noticed extreme crystallization, increased resin production and larger more massive flowersespecially when used with GRAVITY.
HYDROPONIC APPLICATIONS:
At this time, hydro is a big unknown. One thing for certain- DO NOT USE AN AERATOR! If using PURPLE MAXX in the reservoir, it should be added the day before a reservoir change. Best is to use the foliar feed method as far into bloom as possible.
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Most important thing in growing purple weed is to have bud capable of turning purple ... best way to do this would be to choose the best strain possible. Urkle, GDP, or Grape Ape would be best choices but are clone only
The Next Best Thing is...