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It seems like having a significantly cooler night period than day period can help encourage cannabis plants to display red, pink or purple colors. Some growers try to get their plant to artificially display colors by shocking the plant with very cold temps, especially at night. Some growers also recommend hot day temperatures to increase the difference in temperature between day and night. The reason this can work is because it disrupts the uptake of phosphorus, and in some plants this will cause the upper leaves under the light (and the adjacent buds) to turn red or purple. This does not work with all strains. The type of reddening or purpling caused by low temps may sometimes result in smaller yields because non-green leaves may not be as efficient at photosynthesis compared to green leaves. The plant also needs phosphorus to produce buds properly.
The leaves of this plant turned purple over night after that plant was exposed to chilly temps. You don’t want cannabis plants to experience freezing temperatures, which can cause permanent damage for some cold-sensitive strains, but you may go as low as 55ºF (13ºC) without significant problems with most strains.
Cold temps may help the plant purple up, but it will also likely slow plant growth and hinder many aspects of a flower’s development. It’s generally not recommended for growers to turn down the temps just to achieve colored buds, especially at the beginning of the flowering stage – you may be doing more harm than good! If you are looking for purple buds, you’ll get the best results by finding purple genetics that look/smell/taste the way you like. A “true” purple cannabis phenotype with turn purple no matter what you do in the environment.
If you do plan to use cold temps to shock your plant into producing colors, at least to wait until just before harvest so you don’t accidentally reduce your yields. It’s also important to note that just because the buds have turned red or purple, it has nothing to do with their final potency. Purple buds are not any more potent than green buds.
Leaves near the colas may turn pretty colors after being exposed to dark temps, but it may sometimes slow down growth and inhibits proper bud production. You need green healthy leaves for the best bud production in the flowering stage, not purple and yellow leaves that don’t have the phosphorus they need to complete photosynthesis and make energy to product buds. A leaf like the following looks neat but may deliver less energy to your plants.