Of course you have read my previous column (if not click here: BLOG), and you know that we have come to the pinnacle of the cannabis cultivation process. On the Dutch side of the equator it will take a little while before it all happens, because September is quite a way off, but if all is right then you know what I'm talking about. Yes of course: The Flowering Phase.

With outside cultivation, the shorter becoming days and the longer dark periods will ensure that the flowering process is initiated. Or, you just switch around your light schedule from 18/6 to 12/12, then the same thing will happen: FLOWERING!
Note: when growing from seeds the plants will be ready after 1 to 2 weeks of growth (depending on the desired height) and can be transferred so it can flower.  One of the (many) rules of thumb is that a cannabis plant can be put to growth when the plant is just as wide as the pot it's in. 

In the first two weeks of growth the plants will continue to grow and develop a flowering structure and the first buds will become visible, this is also called the 'stretching period'. After the stretching period the plant will increase in height by 50 to 300%, depending on the genetics (Indica or Sativa).

Sativa vs Indica by ASC

The decreasing amount of light by the end of the summer ensures that your cannabis plants know that their lives have come to an end. As mentioned earlier, the cannabis plant measures the amount of dark hours by means of the 'Phytochrome' hormone. The reaction of the cannabis plants is that their reproduction cycle is triggered in order to maintain its species (the survival mechanism of the cannabis plant). Female plants will produce flowers in the flowering phase. These flowers have a raisin layer (trichomes/hash) when the try to 'catch' pollen, so that they can be fertilized. Pollen are produced by male cannabis plants during the flowering phase. The result of the fertilization are seeds; the offspring of the cannabis. This cycle can go on indefinitely with the seeds, and that's why cannabis continues to exist (hopefully forever). But of course we want to make sure that seeds will get in your flowers, because your flowers probably serve a whole other purpose than just seed production. Therefore you always have to make sure that male plants are taken away in time from female plants before pollen can be spread (this usually happens in the second or third week of the flowering phase).

HermieDuring the 12/12 schedule your plants will receive the same amount of light hours as dark hours (12), but also with more than 12 dark hours your plants will remain in the flowering phase. Some growers prefer more than 12 dark hours (I'm not sure if this is advisable, I've personally never experimented with more than 12 dark hours). Giving more than 12 light hours is on the other hand not possible in the flowering phase. If your plants receive more than 12 hours of light then they will become stressed and confused. It's not clear to your plants whether they should grow or flower and therefore they'll go back to the vegetative phase, or worse, they'll become hermaphrodites (hermies). Hermies are female cannabis plants in which the flowers (buds) develop male genitalia (pollen pouches) to fertilize themselves (self pollination). The result is that you'll end up with buds that are filled with seeds and this is often undesirable. PLEASE NOTE: A common mistake made by beginner growers is breaching the dark period by 'peeking' in their growing tent when the lights are off. Even the slightest ray of light may 'awaken' the plants from their sleep, this also goes for plants that are outside and get light in the evening/night from streetlights or garden lights. In both cases the dark period is interrupted, which only results in stress for the plants. Not a good idea!


Karma FlowerFlowering period & Genetics

The flowering period of cannabis plants depends on their genetics. Sativas have a longer flowering period than Indicas, and the flowering period of Hybrids (Sativa/Indica-mix) is usually somewhere in between (makes sense).

  • Indicas flower 7 to 9 weeks
  • Sativas flower 10 to 16 weeks
  • Hybrids flower 8 to 13 weeks


Optimal RH & Temp during the flowering period

As soon as your cannabis is flowering you'll need to decrease the RH (Relative Humidity) in order to decrease top rot risk. The perfect RH in a growing space during the flowering period is between 40 and 50%, and the optimal temperature is between 25 and 30 degrees Celsius. Also the nutritional requirements in the flowering phase will shift from Nitrogen-needy (N) to Potassium (K) and phosphorus-needy (P).


Bare Legs (third week of the flowering process)

Kale BenenWith the 'Lollipopping' technique all excess leaves/shoots in the bottom of the plant can be removed in the third week of the flowering period, so no underdeveloped top forming will occur (saves you a lot of trim work in the end). This means that all plants will have bare legs after lollipopping; women with smooth legs are the best too, aren't they! I do this myself until the third week of the flowering process, after that I don't recommend it because it may affect  the stress level of the plant.


The Flush

I recommend to stop feeding the plants 2 to 3 weeks before you harvest, and only give them water. I call this 'flushing'. Personally I flush three weeks before harvest with water, just straight from the faucet without any added 'flush agents'. (In The Netherlands faucet water can be used because it doesn't contain any chlorine and it's clean and drinkable).

During the flush the big leaves die off and begin to discolor around the top, so 'fall colors' become visible. The plants still use all available/stored nutrients (otherwise the nutrients would end up in the final product). My experience is that flushing has a positive effect on the taste of the final product, the smoke is smoother on your throat, and a pure joint burns slowly and smoothly, without having to light it constantly: WHITE ash!

Flush 1 Sin Mint Cookies

Flush 2 Scotts OG

Flush 3 Shoreline