Cannabis plants go through different stages of life before reaching harvest. These stages are: germination, pre-growth, growth and flowering. Depending on the phase of life, the care and feeding required can vary greatly, in this case we’re going to focus on the flowering period of cannabis and the changing nutritional demands upon our plants.
During the flowering stage, cannabis plants produce our beloved buds. This stage is recognized by the switch from the vegetation stage into the beginning of bud development. Growing cannabis is quite complex, the flowering stage in itself has several stages and many things to consider. We shall explain the need-to-knows of the flowering stage.
When growing cannabis indoors, the flowering stage begins when you change your grow lights to a 12/12 light cycle (12 hours light, 12 hours darkness each day). Getting those 12 hours of uninterrupted darkness each day gives your plant the signal that it’s time to start flowering. In a way the plant “thinks” winter is coming because the days are getting short.
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.
Autoflowering strains of cannabis don’t need special light periods to start flowering, however the cannabis flowering timeline in this tutorial is a good general guideline for indoor auto-flowering strains, too. Their “vegetative stage” lasts about 3-4 weeks, so as long as you start counting at week 3-4 from seed (when they start getting their first pistils) this flowering timeline will generally apply to autos too, though sometimes they finish up faster.
During the first few weeks after being switched to a 12/12 schedule, your plant will be growing like crazy and rapidly gaining height. In fact, a cannabis plant can (and frequently will) almost double in height after the switch to 12/12. This period of super-fast and often stretchy growth is sometimes referred to as the “flowering stretch.”
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!
As part of the stretch, your plant will be growing out its bud sites. Stunting growth at this point could cause the plant to make smaller and fewer bud sites than it would if it were healthy and growing fast.
The mad stretching of the first few weeks will start to slow down in week 3-4, but your cannabis plant will still be growing upward. At this point you’ll actually start to see real buds instead of just hairs (I like to call them “budlets” during this stage) and all the pistils will be white and sticking almost straight out.
Your plant is going to start getting a little picky about the environment and nutrients in week 3-4 so it’s important to keep a close eye on your garden. You need to make sure your plant stays healthy all the way to the end of the flowering stage, and you’ve still got more than a month to go so you don’t want your plant to run into any major health problems now!
As your plant continues through the flowering stage, it’s normal to see a few yellow or discolored leaves near the bottom of the plant, especially in the places where the leaves are no longer getting light. This isn’t anything to worry about if it’s just a few leaves as the plant is putting its energy to the top of the plant and the buds.
By weeks 4-6, the stretch is almost over and you no longer need to pay attention to training your plant. Instead of trying to keep the colas down, from now on you’re doing the opposite – trying to hold any buds up if they start getting too heavy for your plant! Although most of the pistils will probably still be mostly white by the end of week 6, the buds are getting bigger and denser every day!
From now on your plant won’t be making any new leaves or stems. It has completely switched gears away from vegetative growth and all its energy will be focused on growing buds from now until harvest.
The fat young bud of a flowering marijuana plant. At 6 weeks old, your buds should be fattening up rapidly!
It’s normal for some of the bottom leaves to begin to turn yellow as the plant continues to put its energy in the leaves and buds getting the most direct light, though the plant should still be mostly green from top to bottom even in week 6-8. At this point, your plant may start getting much more picky and sensitive to nutrient problems, including those caused by incorrect pH at the roots. Now is not the time to slack off on caring for your plants! It’s normal for some of the bottom leaves to begin to turn yellow as the plant continues to put its energy in the leaves and buds getting the most direct light, though the plant should still be mostly green from top to bottom even in week 6-8.
Once you’ve reached week 8, buds are fattening quickly. Trichomes and pistils are maturing, though new pistils may continue to develop on the buds as they grow.
You are basically just maintaining your plant until harvest. Different strains are ready at different times, but from now on you’re going to pretty much treat them all the same. Keep a close eye on the buds, pistils and trichomes as a whole to help you figure out the best time to harvest to get the effects you are looking for.
Just around 8-10 weeks is when you get to see the buds in their full glory. It’s also when the smell of cannabis often starts to get overpowering!
After Week 8 it’s normal to see leaves turning yellow, in fact there’s not much you can do to prevent it. As long as it’s close to harvest and the yellowing is not affecting your actual buds it’s ok!
You may want to harvest your marijuana buds early if they’re starting to get damaged by nutrient or other problems. Sometimes it’s better to cut your losses than let your buds continue to get beat up! If you harvest your plants too early you can improve many unwanted effects by curing them. For example, these buds probably should be harvested before the buds get any further damage.
Nutrients During Flowering
During the vegetation period, the plants require solid amounts of nitrogen to develop big green leaves, which absorb energy from the light. When the flowering period kicks in, it’s important to continue feeding the plants with nitrogen, otherwise, the leaves will prematurely turn yellow, and the buds will suffer. The buds grow slowly in the first 2 weeks of flowering, make sure not to abruptly introduce an intense amount of nutrients, otherwise the plants can experience overfeeding symptoms. Phosphorus and potassium should be gradually introduced in higher amounts, to provide the buds with their requirements. During the last stages of flowering, the plant still requires phosphorus and potassium, although magnesium and sulfur should be introduced, which will help the plants to develop dank resin and higher quality flowers.
As a rule of thumb, the humidity of the environment should not exceed 50% during the flowering stage, since the buds can become very humid, which can result in undesirable mold. When growing very dense nugs, make sure to drop the humidity level, if the buds are relatively airy, they can handle higher humidity levels.