plantas en prefloración

What’s the pre-flowering stage of cannabis? When, why and how

De: Contributor Grow

The pre-flowering stage of a cannabis plant is a critical period in its life cycle. This phase lasts between 2 and 3 weeks and often occurs after the vegetative stage and before the actual flowering period. During this time, the plant begins to develop its sexual organs, which will determine whether it will produce buds or pollen. Therefore, it is important to understand this stage to be able to optimise the final yield of your cannabis plants.

Anyone who has ever bought cannabis seeds knows that flowering times are an important feature of the different strains, since this sets the timer to determine when growers can obtain maximum rewards, i.e., their precious harvest. Basically, this is the stage where all the TLC invested in the previous vegetative phase begins to bear fruit. Slowly but surely, female plants start revealing their flowers as they prepare to pile up the large buds that will emerge from between the leaves.

When does the pre-flowering take place?

In nature, photo-dependent cannabis plants transition from the growth phase to the flowering stage when they ‘notice’ that the days are beginning to shorten. This starts on the longest day of the year, at the summer solstice, which occurs around 21st June in the northern hemisphere. This is a turning point in nature: autumn is coming; and, for perennial plants like cannabis, that means that it’s time to start flowering and producing offspring.

Indoors, plants don’t feel the change of seasons, so growers need to ‘persuade’ their plants into the flowering phase. This is done by reducing the hours of lighting provided by the grow lights, and usually implies changing exposure times from 16/8 (16 hours of light followed by 8 hours of darkness) to 12/12 (12 hours of light followed by 12 hours of darkness).

The best time to make this change depends on the strain in question and on the grower’s intentions. The great exceptions to this procedure are the autoflowering cannabis strains, which determine when to start their flowering phase autonomously.

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Week 1 of the pre-flowering stage: A change in the photoperiod

Depending on the circumstances, once the cannabis plants ‘know’ that it’s time to move to the flowering phase, a hormone called phytochrome (which is produced as soon as the seeds germinate) is ‘suppressed’ by the red light spectrum that they receive from both the sun and the artificial lighting during the long daylight hours.

Once the plants are exposed to at least 11 hours of uninterrupted darkness (certain sativa strains may require 12 hours or more), critical phytochrome levels are activated. After approximately 5 days in this state, the plants receive the signal to shift to the flowering stage.

The production of other hormones found in the cannabis plant also changes, with a decrease in auxins and an increase in cytokines and gibberellins, for instance. These hormonal changes trigger the development of flower nodes.

Once the change in the lighting cycle is made, a panic reaction is triggered in the plant, which begins to grow whilst producing buds at the same time. At this point, many varieties will start stretching quickly for a couple of weeks before fully immersing into the flowering stage.

Apart from this, there’s hardly any noticeable changes during the first week of pre-flowering. This is also a good time to consider certain training techniques since cannabis requires time to recover from stress. Low Stress Training (LST) is perfect for this, as it doesn’t cause any major damage and allows for maximum light penetration into the flowering shoots whilst the canopy is being flattened.

Week 2: First signs of early flowering

It is in the second week that the flowering cannabis plants start to physically manifest the new phase in their life cycle, although there is still a way to go before the buds become visible. One of the first signs of the pre-flowering stage is the appearance of preflowers.

Preflowers are small, underdeveloped versions of the flowers that will later become buds. Around the second week after changing the light cycle (or approximately Week 4 in the case of autoflowerings), small white hairs known as pistils begin to emerge from where the fan leaves protrude from the main stem of the plant. These areas are known as flowering sites.

In reality, they’re not pistils but stigmas. Pistils are female reproductive organs intended to receive the pollen scattered by male plants (cannabis reproduces by aerial pollination). Therefore, you will start to notice the development of small green balls (called bracts) around the nodes where the pistils grow, and these are the first signs of the real buds. It is from those bracts that two small white ‘hairs’ will emerge. These are the stigmas: a sticky surface that captures the pollen from the male plants for fertilisation purposes, which means that they are responsible for receiving this pollen and taking it to the ovule in the pistils.

On the other hand, male plants develop pollen sacs that look like small round balls that hang from the plant’s nodes. These sacs eventually open to release pollen into the air, which can travel a considerable distance, potentially pollinating nearby female plants.

What’s the pre-flowering stage of cannabis? When, why and how
Differences between male preflowers (a-b) and female preflowers (c-d)

If your plants produce pollen sacs instead of pistils, this means that you’ve got males in your grow, so you’ll need to get rid of them as soon as possible to prevent the development of seeds and to maximise your flower production. This is something that you won’t have to worry about if you use Kannabia’s feminised seeds, as they only grow into female cannabis plants, thereby minimising the risk of pollination and facilitating the production of seedless buds.

Week 3: Buds start to develop

After two weeks of pre-flowering, small sugar leaves also begin to emerge around the pistils, which are part of the buds that will make up the final yield of the harvest. At this stage, your cannabis plants will not have stopped growing completely and could even be 50% larger than they were before the change in lighting. New stems and leaves become more evident in the third week of flowering, and more pistils can be seen emerging from the nodes of the main colas.

Plants are still stretching at this point and are still quite flexible; so, if you haven’t already sculpted their shape much, this is still a good opportunity to work on that flat canopy that can help increase your yield up to 60%.

Towards the end of the third week of pre-flowering, you may begin to notice that these ‘mini-buds’ are taking shape. And vegetative growth will stop a month after the beginning of the flowering (more or less), meaning that the plants will devote most of their energy to flower production.

Cogollos en floración
Buds forming after the first month of flowering

What do cannabis plants need in the pre-flowering phase?

You should also watch out for any nutrient imbalance that may hinder the development of these buds. As a general rule, you should keep a minimalist nutrient plan (remember that less is always more). Having said that, the needs of cannabis plants throughout the flowering phase are different from the ones they have during the vegetative stage: while they mainly need nitrogen while they’re growing, they actually need more phosphorus, potassium, calcium, and other minerals and trace elements to reach their maximum flower power.

Also remember that cannabis plants absorb nutrients better in slightly acidic environments (with a pH between 6.0 and 7.0 in soil, and between 5.5 and 6.5 in hydroponics). Closely monitoring the pH levels will help you prevent burns and toxicity, as flowering plants are more vulnerable to nutrient overdose and don’t recover as well as plants in their growing phase.

Water is obviously another constant requirement. Marijuana plants need less humidity during the flowering stage, so only water them when they absorb most of the water available in the growing medium. You can assess the situation by sticking a finger in the substrate (top 2 – 4 cm), which should feel dry between irrigation sessions. If the soil takes more than 3 to 4 days to dry, you may have drainage problems, so you should add organic matter or make additional holes in the pot.

Lastly, the plants need moderate heat and humidity while the buds are growing. The right temperature levels range between 21 and 26°C during the day, and between 18 and 23°C at night. Experienced growers may sometimes keep the night temperature at 12 – 14°C in the last few weeks of flowering to enhance the purple colour of certain strains.

Decreasing moisture levels is also key to getting dense buds. Start this stage with 55% relative humidity and reduce it by 5% every week throughout the whole life cycle: this should be between 35 and 40% during the last ten days before harvest.

In summary…

The pre-flowering stage is a critical period in the life cycle of cannabis plants. Understanding this phase and providing the plants with the right growing conditions can help guarantee healthy development, which will eventually lead to a successful harvest. If you’ve shown a lot of patience and attention to detail, and you’ve given your plants the affection they need, then you should have mastered the pre-flowering stage. So now you’re armed with all the knowledge you need to turn your cannabis seeds into huge plants brimming with stunning buds.

Kannabia Seeds Company sells to its customers a product collection, a souvenir. We cannot and we shall not give growing advice since our product is not intended for this purpose.

Kannabia accept no responsibility for any illegal use made by third parties of information published. The cultivation of cannabis for personal consumption is an activity subject to legal restrictions that vary from state to state. We recommend consultation of the legislation in force in your country of residence to avoid participation in any illegal activity.

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