In an ideal world, the perfect weed would look, smell and taste great as well as doing you good. That’s the standard for which serious growers aim. With this in mind, some people look to grow purple weed, as they see it as more attractive.
Green v purple - it’s all in the genes
Chlorophyll is what makes plants green. It’s a chemical which absorbs sunlight, which is then combined with carbon dioxide and water to give plants the nutrients they need. This process is called photosynthesis. As the amount of sunlight decreases, e.g. in Autumn, photosynthesis becomes less effective and some plants react to this by allowing the chlorophyll they contain to break down, which has the effect of exposing any chemicals which were previously covered by it. This is why the leaves on many trees change colour in Autumn and it’s also what makes certain strains of marijuana turn purple. So if you are interested in growing purple weed, you need to start by making sure you use a variety with the right genes. Granddaddy Purple is an obvious choice, there are plenty others.
Know about nutrients
If you choose to grow purple weed, you need to understand that what you are effectively doing is convincing the plant that it’s Autumn and that it therefore needs to start shutting down ready for winter. This involves shedding nutrients. It therefore needs to be approached with care, otherwise you may end up damaging your plant. When you are first starting out it may be better to accept less purpling to ensure optimum taste and yield and then increase your attempts at purpling one stage at a time.
Since your aim is to make your plant think it’s Autumn, you need to lower the temperature accordingly. Always wait until your plant is actually flowering before you drop the temperature, in fact you could even wait for another 3 to 4 weeks. Your aim is for the purpling to start about 2 weeks before your harvest. If it starts too soon you may well find your plant ends up looking beautiful but with low yields and or poor taste. When you do lower the temperature, then only do so when the light is off. As a rule of thumb 10ºC is as low as you want to go. Some strains will turn purple at far higher temperatures, so again you may wish to try a gentler approach at first.