Whether you’re just starting to grow cannabis or you’ve been at it for a while, it’s a good idea to know what to expect during the cannabis flowering cycle. The cannabis plant has a variety of characteristics during the different stages of its lifecycle – which include germination, the vegetative stage and the flowering stage – but for many home growers, the final flowering stage is the most exciting. A lot of it is because this stage reveals what the quality and quantity of your harvest will be. Understanding the process makes growing easier. This article will go in-depth into the cannabis flowering stages, so that you can harvest higher quality buds.
Cannabis Flowering Week By Week
The flowering stage begins once the vegetative phase has ended. This usually takes 3-4 weeks, but can vary by the strain, so be sure to consider your strain first. If you are growing your cannabis indoors from photoperiod seeds, the flowering stage starts when you change to a 12/12 light schedule (this is when the plants receive light for 12 hours and are in total darkness for 12 hours). If you use autoflowering seeds, the plant’s genetics determines when this period begins. Once flowering begins, the cannabis flowering stages last approximately 7-9 weeks. They can be divided into the following sub-phases.
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Week 1-3: The Flowering Stretch
When the plants start receiving 12 hours of darkness each day, they “think” that winter is close, and prepare to produce offspring. The first of the cannabis flowering stages, therefore, includes a major spurt of vegetative growth aimed at giving the plant ample size and strength to support those coming buds. This stretch is so dramatic that most cannabis plants double or even triple their height during this time.
This is a good time for your plant. During this flowering stretch, your cannabis plants will still be very resilient and can quickly recover from any problem that they experience. This resiliency also occurs during the vegetative growth stage.
During the flowering stage your plant starts diverting energy from vegetative growth into bud production that it believes will help produce offspring. Without pollen from a male plant, your cannabis plant will use the energy that would go into producing seeds for increasing the size and number of buds that usually contain these seeds.
Some cannabis growers believe the growth spurt during this phase means that your cannabis plants still need the same types of nutrients that were used during the vegetative growth phase, such as nitrogen. Another school of thought suggests that introducing nutrients needed for bud production such as phosphorous and magnesium can limit the amount of stretch and help jump-start the plant's budding by having these nutrients available already. Regardless of which you believe, the plant should gradually be switched from a vegetative line of nutrients to a blooming line throughout this period.
You will also notice single leaves starting to bunch up at the top of the main colas of each plant. White pistils will emerge from the middle of these bunches of leaves. This is a sign of new buds being produced.
If you are going to try your hand at training your plants, now is the time. Low stress training (LST) involves bending the stems of the branches gently so that you have a flat canopy at the top. This flat canopy is critical to ensure even distribution of light to all parts of the plant. For outdoor grows this training is generally unnecessary as the sun will naturally pass across most of the plant's surface throughout the day. Sections without direct access to light will not produce mature buds and are often removed so the plant can put more energy into the parts that do receive plenty of light.
Week 3-4: Formation of “Budlets”
The flowering stretch (spurt of growth) starts slowing down when your cannabis plants start forming tiny buds (also known as budlets). Now, we enter the second leg of the cannabis flowering cycle. Each stage of the bloom cycle is more critical than the last, so you should be very careful since any mistake or problem can affect your yield or harvest quality.
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Use this time to observe your plants carefully for any signs of problems. The easiest signs are the symptoms visible on the leaves. For example, nutrient toxicity or "nute burn" (excess nutrients that cause something that looks like a burn on the leaves) causes the tips of your leaves to become brown or yellow. If you don’t reduce the amount of nutrients provided, this burn will spread to other parts of the leaves, and the plant may be severely affected. If untreated, your plant will no longer be able to manufacture its own food.
Nutrient deficiencies are slightly less detrimental as too many nutrients (because it's easier to introduce nutrients to the plant tissue than remove nutrients, and there are some that cannot be removed that are called 'immobile nutrients'), but you should still keep track of what you feed your plants and adjust as needed as soon as you determine a problem. Your plants can still recover to some extent, but it's still much better not to have any problems to fix in the first place.
You will also notice that some leaves at the bottom of your plants will become yellow around this time. If only a few leaves are affected, don’t fret. It is normal for some of the bottom leaves to yellow if they aren’t receiving ample light (the canopy is thick at this point). The plant is extracting all the nutrients from those leaves to keep the developing buds well taken care of. Plants are intelligent; they don’t want to waste resources on components that aren’t productive!
These weeks are exciting because they mark the time when the plants begin giving off a more distinct odor.
Week 4-6: Fattening of the Buds
Next up in the cannabis flowering stages is the fattening of the “budlets.” The tiny buds described earlier start to fatten quickly. This fattening happens rapidly, and you will still see the pistils sticking out of them.
The “flowering stretch” is almost no more during these weeks, so there is minimal need for you to continue training your cannabis plants. The plant is now fully focused on its buds.
However, you can still do some training if you notice that the canopy of some of your plants isn’t as flat as you would like it to be. Keep in mind, training during this time can be risky. Unlike during the flowering stretch, any training done now is more stressful to the plant as vegetative growth has mostly stopped. The plant can recover but try as much as you can to avoid this type of training, since it could significantly slow the fattening of your buds.
Since your plants aren’t growing any more leaves at this point, do everything you can to preserve the existing leaves. First, provide the correct amount of balanced nutrients, so that nutrient burn or nutrient deficiency doesn’t cause leaves to yellow or become necrotic. Second, provide enough water since transpiration will be taking place at a high rate. Excess stress from improper humidity, heat, or light levels can also cause leaves to yellow and drop off.
Don’t try your hand at removing leaves (defoliating) unless you are experienced at it and can strategically remove the correct leaves that will expose additional bud sites.
You want to maintain as many leaves as necessary to create a full canopy because if you remove too many after this point, your plant may not have enough foliage to absorb enough light to maximize yields. However, if you have plenty of healthy leaves, there is a “reserve” of leaves that will help the plant continue to thrive.
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As this portion of the flowering stage progresses, the majority of the pistils will remain white, signifying that the buds are continuing to get denser and bigger with each passing day.
Week 6-8: Ripening of Buds
When the buds start to ripen, you’re beginning the next cannabis flowering stage. Any vegetative growth has completely stopped by this point, and all energy is devoted to the cannabis plant’s final stages of life. The buds will grow largest during this time, which is why it is important not to provide any nutrients that promote vegetative growth. This would be wasteful and even counterproductive.
Why are nutrients like nitrogen counterproductive at this point? The reason is that these nutrients are not being used to the same extent that they were during the vegetative stage. This causes an accumulation in the leaves that negatively affects the quality of the buds after harvest. If too much nitrogen is present, the plant can even get stressed and revert to vegetative growth or self-pollinate and start producing seeds, which negatively affect the quality and quantity of harvest.
The bottom leaves on some plants begin yellowing and falling off during this stage while other plants begin losing leaves during Week 4-6 of the flowering phase. Nevertheless, you still need to be vigilant so that you don’t mistake a problem for normal leaf loss. If all is as it should be, your plants should stay full and green with just a few bottom leaves discoloring or possibly falling off.
During this portion of the many cannabis flowering stages, you may notice buds that form beneath or on the sides of existing buds. This phenomenon is called “foxtailing,” and while it can be observed naturally with some strains, it is more typically a sign of environmental stress, either from too much light or too high temperatures. Find out which applies to your situation and adjust accordingly.
For example, if your plants grew taller than expected and are now close to your grow lights, then you should raise the lights higher so that the plants don’t suffer from light burn.
Or, if you find that sections of your grow room have a higher temperature than what is recommended for plants at this stage, increase the air flow so that heat can be exhausted more efficiently.
Excess light or temperature can bleach or burn the buds (causing them to be discolored). The buds will also lose some of their potency (THC) since evaporation will cause the plant to lose some of its cannabinoids. Do you still need convincing about the importance of maintaining the right light and temperature levels?
Week 8, and Beyond: The End of Flowering
The exact week on which you will harvest is mainly dependent on the strain that you are growing. The harvest window is typically around a week long, after which THC will start degrading into CBN, which is less potent and produces a sleepy feeling. Near the end of flowering, the pistils on most strains (but not all) will change from white to orange. It is a signal that new buds are not being produced by the plant anymore and harvest time is likely close. The trichomes of your plants will turn from clear to milky as they increase in THC, and then start changing color progressively to amber, signifying THC that is degrading into CBN. Both phases of this process overlap somewhat, but most growers believe your plants have reached their full potency level when roughly 5-30% of the trichomes are amber, and the rest are milky.
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Be careful with your plants at this point. They are extremely sensitive to the conditions around them during the end of the grow. For example, without ample airflow excess moisture from transpiration can become trapped inside the constantly growing buds, causing the dreaded "bud rot" (botyritis, or gray mold) that often spreads and destroys entire harvests.
It is also common for some buds to become heavier than their branches can support during this phase of the cannabis flowering cycle. You may, therefore, need to support them so that they can stay upright. Use tools to prop your plants up – you can find them online or at many garden supply stores.
The end of the cannabis growing cycle also brings about the most distinctive “weed” odor. You can expect the smell to reach overpowering levels. Do not be surprised if neighbors and visitors ask about the smells drifting from your garage or wherever you are growing your indoor plants. Exhausting all air through a carbon filter can help with odor management.
Shortly before you are ready to harvest your buds, you should flush your plants. Flushing is a simple process where you stop giving your plant nutrients, and instead, feed them pH-appropriate water. You should flush your plants from a few days to a few weeks depending on the length of the strains’ flowering stage and your grow medium. Soil retains more nutrients than hydroponic mediums and so requires a longer flush.
The purpose of flushing is to give the plant a chance to utilize all the nutrients in its system so that they don’t taint the taste and smell of the buds. Flushing can also help remove any salts that have precipitated and built up in the grow medium. In short, flushing provides a final chance to improve the quality of the final harvest.
The flowering stage is rewarding, and if you understand the process, you can gain more from it. As you can see, there are five distinct cannabis flowering stages, each with their own characteristics and requirements. Proper oversight of each of these stages puts you firmly on the path to harvesting the biggest and most potent buds that your cannabis strains are capable of yielding.
Keep in mind, this article only provides a general guide. You’ll still need to tweak your process based on the specific cannabis strain you plan to grow. However, remember that every cannabis strain goes through theses stages – even the easy-to-grow autoflowering strains. The main difference with these strains is the fact that they reach the flowering stage regardless of what light cycle they're on. For them, the onset of flowering is triggered by their genetic code rather than a change in the number of hours of darkness each day. That is precisely why autoflowering strains come highly recommended by A Pot for Pot.
Growing marijuana can be easy – especially when you understand the cannabis flowering stages. Have fun growing your next cannabis plant, and once you're done flowering check out our article on harvesting and drying!
FAQ About Cannabis Flowering Stages
What is the best soil for growing cannabis?
It’s important to get into the specifics before you rush into ploughing a field. Balcony growers are probably best-off using pots and containers that can be moved easily, while a sun-drenched, secluded cannabis plantation may require serious earthworks to create a fertile super soil. Always take care to maintain a pH of 6.0–7.0 for any soil grow.
What do cannabis plants look like in the beginning stages of flowering?
Your plants will transition to flowering and start forming tiny buds (also known as budlets).
When are cannabis plants ready for harvest?
There are two main techniques growers use to identify the right time to harvest marijuana plants. These two techniques are the "Pistil Method" and the "Trichome Method". For the Pistil Method, if the vast majority of pistils (hairs) are still white and sticking out straight, then it's too early to harvest. For the Trichome Method, look at trichomes under a magnifier to harvest cannabis buds with the right THC levels.