Flowering Stage

Flowering Stage Grow Room Environment…

Cannabis plants during the flowering stage need light for 12 hours per day, this means that you should have your lights on for 12 hours on and off for the other 12. Preferably your light should be on during the night time because this helps to keep the grow room cool as the ambient temperature is lower. In order for this to be more manageable for those of you with less time on your hands, we recommend using a hydroponic timer, not only is this hassle-free but it is also the most accurate and simple form of managing your light cycle as the light is guaranteed to come on at the same time every day, offering consistency and sustainability to your plants and thus optimising there overall growth.


Grow Room Lighting

Cannabis plants, in the flowering stage, perform best under High Pressure Sodium Lighting. However, for those of you on a budget who can’t afford to change your lights from Metal Halide Lamps, used primarily for the vegetative stage, these will still work during the flowering stage. Alternatively, you can purchase Dual Spectrum Bulbs which are always a good investment as they work to a good standard throughout both the vegetative and flowering stages of growing cannabis indoors.

A 400watt lamp will cover a 3×3(ft) space. A 600watt lamp will cover a 4×4(ft) space. A 1000watt lamp will cover a 5×5(ft) space.

A 400watt lamp should be kept 30cm(1 foot) away from the plants canopy. A 600 watt lamp should be kept 45cm(1.5 ft) away from the plants canopy. A 1000 watt lamp should be kept 60cm(2 ft) away from the plants canopy. A good method to make sure the distance form light to plants is sufficient is by putting the back of your hand underneath the lamp for 30 seconds, if it’s too hot for your hand then it is too hot for the plants. See the grow light info on this site for more.


Temperature And Humidity

During the flowering stage, while the lights are on the grow room should be 25-27ºC, while the lights are off the grow room should be 20-22ºC.

The humidity of the room should be around 45%, this can be measured using a grow room thermometer with built in humidity reader, most good quality grow room thermometers will have this.



The grow room will need 1 medium sized oscillating fan(around 12-16 inch) for every 2 lights used. The medium sized oscillating fan should blow directly into the gap between the grow room lighting and the plants canopy, DO NOT blow a strong wind directly at the plant as this will cause the leaves to dry out and therefore slow down growth.

The intake fan and an exhaust fan when working in conjunction with each other should always have enough power to completely exchange all of the air in the grow room within 5 minutes, meaning you will always have sufficient amounts of clean air to optimise your cannabis plants overall growth. A 5 or 6 inch exhaust fan(depending on model and heat being produced) per 2 meters squared(2 400 or 600 watt lights) with a suitable intake is usually adequate.


Smell Control

It is very important that your exhaust fan, with a carbon filter connected, is able to sufficiently move more air out of the grow room than the intake fan brings in clean air to the grow room. This results in a negative pressure in the grow room which is essential to control and maintain the smell of cannabis plants.  A carbon filter will reduce the amount of air a fan can move by 30%, take this into account when measuring the CFM ratings of the 2 fans. A fan speed controller can be used to ensure the correct temperature and a negative pressure is maintained. We usually advise that you spend a little extra money on a good quality carbon filter as a cheap budget filter will not fully clean the air that passes through it, this is especially important in the flowering stage as the odours given off by maturing buds is extremely strong and distinctive.

Feeding Your Plants…

When purchasing nutrients for your cannabis plants we advise that you use the same brand for each product. For example, your A+B Nutrients should always be from the same company as your PK13/14 and your Amino Acids. Any good quality nutrient company will usually supply a flowering stage feed chart for their range of products, alternatively you can ask in your local hydroponics shop, providing they sell the brand of nutrients that you have used, you may also be able to find the feed chart for your particular cannabis plant nutrients by doing a simple search online. Never mix your cannabis plant nutrients directly together, when mixing your nutrients the method that we recommend is to firstly fill up your bucket or water drum with the desired amount of water and then add each nutrient individually.



If you decide to grow cannabis hydroponically it is essential that you purchase a PH tester, PH-up alkaline solution, PH-down acidic solution and preferably an Electrical Conductivity Pen (EC Pen). Coco and soil, when compared to a full water hydroponic growing system, are more forgiving with regards to PH however, you can expect a reduction in yield if you do not adjust the PH of your nutrient solution according to the needs of your cannabis plants.The PH of a hydroponic nutrient solution should be 5.6 – 5.9, the PH of the nutrient solution for feeding soil or coco should be 6.0 – 6.4. The roots of a Cannabis Plant are unable to successfully intake all of the required nutrients and minerals if the PH is not within the required range. In coco and soil grow room set ups, PH adjustments should be made after all of the nutrients have been added to the water whereas in hydroponic water set ups the PH will need to be adjusted every day or two so it is important to check the PH of your nutrient solutions regularly.


How Much Should I Feed My Plants?

During the first two weeks of the flowering stage a cannabis plants need for hydration will begin to increase quite rapidly each day, as your cannabis plants progress further into the flowering stage you will visibly notice the plant putting on more mass and therefore its need for nutrients will continue to increase until the day that you harvest your crop. Cannabis plants tend to drink a lot of water during the last stage of the flowering stage when the buds are becoming larger, do not neglect your cannabis plants, ensure they are always fully hydrated. If you are using a soil or coco set up you can visually inspect the medium and pick up the pot to see how heavy it is, if the pot is dry and light then this is a clear indication that need to feed the cannabis plant. In soil or coco set ups you should feed the cannabis plant clean water once every 7 days to flush some of the excess salt build up out of the medium. In a hydroponic setup you will need to top up the reservoir as it empties, a hydroponic nutrient solution will need to be drained and replaced every 7 days to avoid inconsistencies in the nutrient solution, this is essential for optimal health of your cannabis plants.


Flushing Your Plants

A plant needs to receive completely clean water that has been PH adjusted only for at least the last 7 days of the flowering cycle, although some growers like to flush for up to 14 days. If you are growing in soil or coco you should either start the flushing process by completely soaking your medium above a drain or bath so that the waste water can run off, doing this removes all excess salts from the medium to allow your roots to access clean water. If you can’t move your plant to a place that allows you to drain the waste water away you should ether pump it from the growing tray with an electric water pump or just go the whole 14 days of clean water only to compensate for not washing the medium, you can stop giving a plant nutrients at the end of week 6 or 7 if you do not want to go as long as 9 weeks. If you are a cannabis grower that does adjust the PH you should still be adjusting the PH of the clean water.

Below you can see a 9 week flowering stage feed chart i drew up for using House & Garden products, flushing is the 9th week.

flowering stage

The Flowering Cycle…

When your cannabis plants have reached the desired size you will need to adjust your light timer settings so that there is 12 hours of light and 12 hours of darkness, when your lights are off there should be no other light from any other sources on your plants at all. Avoid entering the grow room during the hours of darkness as other light will leak into the set up and the cannabis plants will become confused and stressed. In summer months we advise that you have your lights on during the night time because the ambient air is cooler which therefore helps to maintain the correct grow room environment and temperature.


Plants Grow Fast In The First 2 Weeks Of Flowering

During the first 14-21 days of the flowering stage, a cannabis plant will enlarge by up to three times its original day 1 of flowering stage size. After 21 days the growth of the plant will begin to slow down and the plant will start to produce buds. If you use the SCROG method you should have stopped topping the plant at the end of the vegetative cycle. You should still be pulling the branches through the horizontal screen to keep the plants canopy as flat and wide as possible up until the plant stops stretching. Once you have placed each branch in its final position it will be around 14th 17th day of the flowering cycle. Now you should start to cut off anything that is below the screen with a clean pair of scissors, his is because anything that is below the screen will not receive much light and is just going to simply waste energy that could be going into bud production. A lot of people make the mistake of pulling all the fan leaves off thinking that they are blocking light to the buds, when in actual fact it is the big fan leaves that absorb the most light for photosynthesis to occur, we like to think of these as the plants solar panels!


The Buds Begin To Grow

After 2-3 weeks you should begin to see small clusters of white hairs appearing from the shoots, this is the first sign of bud production. At around week 4 the buds should be slightly frosted with resin and will begin to develop a strong, distinctive cannabis smell. As the 5th week of flowering approaches the buds will become denser quite quickly, if you think your buds are looking slightly small, try not to worry because throughout the last 2 to 3 weeks a cannabis plant gains a lot of mass. Throughout this whole time you should be doing your best to maintain the correct environment and feed the plants correctly in order to optimise growth and therefore final mass. Many people wonder how long the flowering/budding cycle of a marijuana plant is? The flowering cycle varies depending on the strain you are using, if you have purchased seeds then the flowering time should be on the packaging, this time is not exact, just guidelines that the seed company have provided.