Purple Phenotypes refer to plants that express ‘purple’ chlorophyll. Some plants developed this as a survival strategy in low-light environments.
For the most part, purple phenotypes may be divided into two basic categories. In the first category, the plant automatically starts producing the purple color at a specific time in the plant’s life cycle. In other words, it is a pre-programed event that the plant consistently activates; many growers are familiar with this.
The second category of purple phenotypes is triggered by temperature. When nighttime temperatures drop to (or below) 55 °F for at least 3-4 days, it triggers the production of the purple chlorophyll. This is why, especially for sativas with lengthy flowering times grown outdoors, some cannabis strains start changing color in late October and early November. These winter months are colder with shorter days. Once the purple chlorophyll production process has started, if temperatures rise, the purple chlorophyll remains. Some of Steep Hill Halent’s clients have learned that chilling indoor grows with an air conditioner while their plants are resting during their dark time works well to express this purple color characteristic.
Purple phenotypes basically come in 3 different colors: purple, red-brown, and bluish purple (indigo). Distinguishing the difference between these colors is useful in typing phenotypes.
Download full PDF report — Purple Urkle
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