For the flowering stage, you should aim for a relative humidity of around 40–55%. The easiest way to achieve this, without getting an air humidifier, is to attach a dimmer switch to your exhaust fans. With a dimmer, you can vary the speed of the air extraction and therefore influence the climate in your grow room. Moreover, an exhaust without a dimmer always operates at full speed even if it isn’t needed. This will not only waste electricity, but also creates more noise than necessary.
With a simple dimmer, you can set up your exhaust to suck away less moist air during the first few weeks of vegetative growth so your young plants develop more quickly. As soon as the plants become bigger, you can let the exhaust do a bit more work as they start to produce more moisture. In fact, once your plants are in full bloom around the fourth week of flowering, you should make sure your plants receive no more than the 50–55% RH threshold.
As harvest is just around the corner, it’s good to keep any fan leaves you trim from your plants as they too contain THC and can be later used to make hash or kief. More about this in our harvest section.
After weeks of mounting excitement, the long-awaited moment for harvest is finally within arm’s reach. Plants have moved quickly through their first three weeks of flowering, undergoing a real transformation. White pistils have emerged, forming the foundation for the buds over which you have been drooling in anticipation.
Too high humidity in the last few weeks of growth can lead to the development of mould and mildew on your buds. This is because the moisture gets trapped within, creating an ideal breeding ground for a host of pathogens. It’s worth noting that strains that develop particularly hard buds have a greater risk of developing mould than those with an airier structure.
If you grow strains with an average flowering time, the majority of bud development will occur by the 6th week of bloom. In the last two weeks, the buds will mostly be ripening and not really growing much more in size. At this point, the previously white pistils on the buds will now slowly turn amber-brown. Depending on the strain you are growing, as well as environmental factors, the ripening of the buds can take a variable amount of time to finish.
Part. 1: The Germinating Phase. Give your seeds the best possible start in life by reading our definitive guide to germination.
Flowering cannabis plants require a specific set of climatic conditions to thrive. No matter the stage of growth, cannabis needs good ventilation to ensure robust health. In terms of humidity, flowering plants need significantly less moisture in the air than seedlings or early vegetating plants.
Enzymes take care of reducing the salt accumulation in your soil that can come from feeding additional nutrients. After using the same bottle of nutrients for a while, you will sometimes notice a white, crystalline deposit on top of it. These are the same salts that also accumulate in your container over time. By growing with organic nutrients, you can reduce the accumulation of these salts, as these contain considerably lower levels than mineral nutrients.
Learn all you need to know about the final weeks of the cannabis flowering stage, including ideal climatic conditions, how to know when to harvest, and more.
Week 3-4: Budlets Form
These buds are ready to start flushing – white pistils have nearly all darkened and curled in
(learn exactly when to harvest so your buds produce the right effects)
Many growers choose to give their plants a 2-week flush before harvest to help make sure the plant has used up any additional nutrients that may affect the taste or smell of the buds.
During week 1-3 of the flowering stage, your plant will mostly be producing new stems and leaves as it grows taller. Right now your plant is still very resilient and can handle problems just like in the vegetative stage. However, it’s still very important to avoid problems and take great care of your plant!
Week 1-3 – Transition to Flowering
Raising nutrient levels at this stage is not recommended as it won’t stop the yellowing and can possibly prevent your buds from fattening up as much as they could have (cannabis wants relatively low levels of nitrogen in the flowering stage for proper bud growth).
If your leaves are already turning yellow in week 6-8 it’s too early! Early leaf yellowing is likely caused by either a nutrient problem or light burn (which are both much more common in marijuanas flowering stage). React quickly to problems so you don’t hurt your yields!
Outdoors, it’s also the days getting shorter that cause a cannabis plant to start making buds in late summer, but outdoor buds develop on different schedules depending on the local climate. This tutorial is meant to explain how a cannabis plant usually develops when grown indoors, since that is done under controlled conditions, and plants tend to grow the same way.
Pre-Stretch – just before 12/12
You can maximize marijuana yields by focusing on the right factors each week of the flowering stage. If you know what your cannabis should look like week-by-week, you'll also be able to quickly tell if something is going wrong!