Purple cannabis flowers are some of the most memorable buds a grower can produce. The contrast between green and purple makes for a delicious looking product with huge bag appeal. The purple in cannabis is created by Anthocyanidins, which are the same water soluble compounds that give fruits such as berries and grapes their recognizable colours.

Genetics, Genetics, Genetics

A cannabis strain needs to have a genetic predisposition to turning purple, without this you cannot use any of the methods below to induce ‘purpling’ of the flower.

Within a certain strain there will also be sub phenotypes that will have a greater concentration of anthocyanins. This is where “crop hunting” or selective breeding comes in. If you want purple flowers crack a number of seeds. Take clones from all of them before flowering. The ones that end up being the most purple are the clones you will want to save and turn into mother plants.

Meatbreath by Thug Pug genetics is one of the most purple strains I’ve come across.

Bringing out the Purple

So you have genetics that have the potential to produce beautiful purple flowers. There are a number of steps you can take to increase anthocyanin production resulting in more purple flowers. The majority of these methods are gentle ways of stressing the plant.

Cold Air Temps During Late Flower

The most common method is to reduce air temperature late in the flowering cycle (typically after week 6 or 7 of flowering). Temps can be brought into the low 50’s if possible (10C).

This method can be difficult for many growers because of the energy required to cool a grow room to those kinds of temperatures. Your AC will be fighting the lights and a large amount of energy is required. Luckily for DWC growers there is a much easier method.

Cold Water Flush in DWC

My favourite method is shocking the roots with ice cold water during the flush phase. In the winter my ground water is in the 40s and is more than sufficient for increasing anthocyanin production right out of the tap.

In the summer, or for those living in warm climates, reducing the temperature can be done by adding ice blocks or reusable freezer packs to the DWC water reservoir.

Long Flush in DWC

In addition to using cold/ice water during the flush, a long flush cycle also helps bring out dormant purple colours in cannabis flowers. I have been known to flush up to 14 days at a time, though 7 days is usually plenty.

Reduced Light Cycle

During flower your light cycle is typically 12/12 for the duration of the 8-9 week flowering phase. Reducing the light cycle to 10/14 or even 9/15 is another way to gently stress the plants and remind them it is time to finish.

Staggered Harverst

In my experience the flowers at the top of the canopy (with the most light exposure) tend to produce the most anthocyanin, or simply put are the most purple.

A staggered harvest removes only the top colas, allowing the green buds below the mature and develop into purple berry resembling. I will usually remove colas every two days. This has the added benefit of splitting up the otherwise tedious task of trimming your flower. I always end up with better trimmed cannabis when doing a staggered harvest because I am not rushing to try and trim the whole batch at once in a trichome induced daze.

Are Purple Flowers Better?

There is no evidence that purple flowers provide any benefits to the end user outside of those brought on by aesthetic appeal. A study that looking into the safety of anthocyanins found that they also pose no risk to the end user. They confer an anti-oxidant benefit which could be beneficial when ingested, but will not have any impact on smoked or vaped flower. When making cannabutter water-soluble compounds are typically removed, as they are high in chlorophyll. So it is unlikely that there will be any quantitative benefit in edibles either.

You don’t grow purple buds for higher THC or CBD. You do it for the looks.