Flowering Stage

Understanding the flowering stage of the marijuana plant can be tricky, but with practice it becomes more (dare I say it) natural. Take the time to learn the fundamentals and practice; once you know what you are doing, it gets easier over time. 

I can’t say this enough:

The flowering stage is essential to the life cycle of a marijuana plant. This guide will teach you about this stage so that you can be a better grower. It will also explain each exciting milestone and provide tips on how to optimize this time to produce potent buds and high yields. Keep reading or jump ahead to your favorite section.

After an entire season of caring for your marijuana plants, it is reasonable to think you can relax during the flowering stage of their life cycle. This, however, is one of the worst things you could do, as this stage needs just as much attention – perhaps even more than the earlier stages.

During the vegetative stage, a cannabis plant grows just like its common name – a weed! It was only concerned with growing new stems and leaves and did so rapidly. The vegetative stage is straightforward, and possibly one of the easiest times for a grower. During that time a marijuana plant can recover from just about anything. If you happen to run into problems (such as an infestation or injury), you can nurse your plant back to health with a little TLC.

Tip: make sure to download my free Grow Bible for more information

But the flowering stage is not as easy.

Not only do cannabis plants grow differently, but they are also a lot more sensitive. Here is when all your training is going to be put to the test because there is very little room for error. You’ve already invested so much time and effort into your plants, don’t ruin the harvest this late in the game.

When Does the Flowering Stage Begin?

Despite the name, the flowering stage doesn’t start with the formation of flowers. Flowering occurs a few weeks into the flowering stage. In fact, it doesn’t even correlate to when you induce flowering.

In fact….

The flowering stage begins when the cannabis plant notices a change in light. This is how it knows winter is coming.

Many people mistakenly think that this change means a decrease in light. Actually, the change is measured by an increase in the amount of continuous darkness. Soon after the strain’s threshold of darkness is met, the plant will grow rapidly, gaining height and stretching. Some plants may even double in height during the first two weeks of the flowering stage.

The stages of flowering

‘In most strains, the first signs of female flowers appear one to three weeks after introducing flowering with the 12-hour photo period.’ ~ Jorge Cervantes

In the first 1-3 weeks a plant will produce new stems and leaves, but at the end of the month that growth shifts to bud formation. The beginning of the flowering stage is dedicated to growing all the necessary parts for a bountiful harvest; any problems during these crucial weeks will impact a plant’s yield.

If plants are grown outdoors, when your plants flower depends on the time of the year and your location. Some strains may start the flowering stage earlier, while others may have an extra-long threshold for darkness, causing them to stay in a vegetative state longer. If you are growing indoors, changing your grow lights will trigger the change.

At the start of the flowering stage, the internodes (those spaces between the leaves) decrease, and the plant’s growth slows down. It will continue to grow upwards. It may seem like your plant stopped growing, but there is a lot of growth occurring in those first few weeks. Pay careful attention and give your plants the right amount of nutrients at this time.

How to Trigger the Flowering Stage

If you are growing outdoors, the flowering stage will begin naturally. However, sometimes you might want to induce flowering.

Why would you do this?

Perhaps, you need your plants to finish growing sooner (for whatever reason). Inducing the flowering stage can help you harvest sooner. In this case, you will merely simulate darkness for 12 hours a day so that your plants know it is time. A blackout sheet over your plants or greenhouse can be used outdoors to simulate darkness.

Growing indoors is different.

In an indoor setup, the flowering stage will not begin naturally. You provide sunlight via artificial lights and change the lighting schedule to start the stage. A cycle of 12 hours of darkness and 12 hours of light will tell the plant that it is time to flower.

But there’s a catch.

You’ll need to ensure your plants receive absolutely no light for 12 uninterrupted hours. If that darkness is interrupted for even a few seconds, your plants may delay flowering, or become hermaphrodites. You may also need more or less than 12 hours of darkness, depending on the strain. Some strains need as much as 14 hours of darkness!

Autoflowering strains

Autoflowering strains are the exception to this process. They don’t need continuous darkness to begin the flowering stage. Instead, they start after a predesignated amount of time.

That’s not all …

These strains grow faster as well. The vegetative stage of these types of strains typically lasts for 3-4 weeks, meaning their flowering stage should begin after around one month of growth.

Spotting the First Flowers

Not sure if the flowering stage has begun?

If it has, you’ll start to notice some interesting changes in your plants. It may take a couple of weeks, but your plant will stop growing and start flowering. You’ll see that it is no longer producing leaves, but instead, small white pistils begin to grow rapidly along the surface of the plant. You’ll also start to notice flowers growing on the buds.

Here’s the deal:

Now is the time to pay special attention to these flowers. This is when your plants start to clearly reveal their sex. During this time, males create a pollen sack, while females begin to develop pistils. The male plants may also continue to grow taller while the females do not. This is so they can drop their pollen onto the female pistils.

Male vs. Female

Let’s talk about sex.

During this time, both male and female plants will produce flowers. Male flowers are smaller with a yellow, red, purple or pale green color while female flowers will have two hairy, white stigmas.

If you want your cannabis plants to produce potent, THC-rich marijuana, pay attention during this time. This is when you should look for those male plants and remove them from your garden. If they fertilize your females, it will be too late.

But that’s not the only thing to look out for.

In addition to the emergence of flowers, you’ll also notice that the internodes have extended. You may also see some leaves covered in a thin, transparent resin. It will look like your plants are stretching and covered with dew. This resin is a teaser of what’s to come but isn’t worth sampling yet, so don’t get too excited just yet.

I can’t say this enough:

Be patient!

By the end of the first month of the flowering stage, you may notice small clusters forming from the female flowers. These clusters are called buds. They are the same buds that you will eventually harvest (yay!), but they are not quite ready. You’ll need to do a bit more work before it is harvest time.

Nutrients during the start of the flowering stage

You’ve entered the flowering stage, so pay attention.

Your plants will need a different set of nutrients then before. Phosphor and potassium are now the priority, and your plants will need enough of it to keep up with all the rapid changes that occur during this time.

Unfortunately, many growers mistakenly increase these nutrients too rapidly while decreasing the nitrogen too soon. Phosphor and potassium are important, but so is nitrogen. If your plant does not get enough nitrogen, it could develop a deficiency.

TIP: Looking to buy seeds? Visit the ILGM seed shop

Keep in mind,

The flowering stage is hard on marijuana plants. Your plants are going to be very sensitive to both their nutrients and the environment, so keep an eye on them. Pests and diseases could be fatal at this point, and there’s still at least a month to go.

Maintaining healthy plants during flowering

Here’s the deal,

Your plants should be full, lush and green when trying to form buds; otherwise, the quality of your harvest will suffer. Any discoloration (such as yellowing leaves from a nitrogen deficiency) or other signs of stress should be nursed back to health before beginning the flowering stage.

If you use nutrients, use a flowering formula during the first month of flowering. Do not change your nutrient solution until there are obvious signs of flowering. You should see many stamens and pistils.

Use the correct nutrients.

Flowering formulas are designed to meet the high demands of the flowering period, but a vegetative formula will make sure that your plants have the nutrients that they need to flower successfully.  So use the vegetative formula until you know you are flowering for certain. Then once you reach the flowering period only use them for the first month, if possible.

Do not overfeed your plants

Nutrients should not be used in the final weeks of flowering.

If you notice a few leaves falling off, do not be alarmed. This is normal, but only in areas where the plant is shaded (such as lower leaves). These leaves do not matter as your plant is now diverting its energy to the top of the plant and the formation of buds.

However, if you notice discolored leaves or a rapid loss of leaves, you may be giving your plants too much fertilizer, or it may have a disease that needs immediate attention.

Learn to recognize common marijuana diseases

Training during the start of the flowering stage

If you’re growing indoors and plan to train your plants, the first month of the flowering stage is the time to do it.

Why would you do this?

Training helps maximize the space in a grow room, and it can also increase your final yield. During the beginning of the flowering stage, the stems are flexible and can be bent without breaking. However, as the stage continues, they will become woody and unable to be trained.

This technique of gently bending stems is called low-stress training. During this process, stems are bent and trained to grow outward instead of just up. When practiced, it provides a flat even canopy for cannabis plants so that more of the plant is exposed to its light source.

People who successfully grow know how to train their plants.

Low-stress training can increase your yields by as much as 40%. Just remember to only train during the first month of the flowering stage, while the plants are stretching.

The Second Month of Flowering

As the flowering cycle continues, you’ll begin to see more leaves, branches, and buds. Everything will grow wider and thicker. Your plant may even start to look like a Christmas tree with the bottom leaves growing out further than the top.

This is a good sign of a healthy mature plant.

What’s actually going on?

The second month is when cannabis begins to look ready for harvesting. The number of calyces on the plants continues to rise. That transparent resin from the first month darkens and develops a strong odor. The buds expand and extend.

Support your favorite lady

All this growth can lead to problems; if you are not prepared. Your plant will be bearing a lot of weight and may need support to stay upright. Those colas are heavy!

What can you do?

One way to help it is with a trellis system made of string or wood. You could even use a metal spring system that adjusts the weight of the plant as it matures.

That’s not all to look for.

You may also notice some of the bottom leaves turning yellow. This is because the plant is putting its energy into the leaves and buds that are getting the most direct light. Most of your plant should still be green, however.

Tip: make sure to download my free Grow Bible for more information

What else can you do?

Keep an eye on the airflow. Make sure your plants receive plenty of circulation during this time. This is particularly important when growing indoors. Marijuana plants grow wide during this period, and they have likely grown closer together. A lack of air flow can easily lead to mold, bacteria and fungal infections.

Identifying the Sex of Your Plants

You may have already identified and removed the male marijuana plants before the flowering stage began, but that doesn’t mean you are necessarily out of the water.

Watch out for sneaky hermes!

It’s not uncommon for a hermaphrodite to develop during the flowering stage. These plants have male sex organs that will pollinate your precious female plants. So check again during the flowering stage to be certain.

By the second month of flowering, if there are any males in your garden, it’s almost too late. At this point, the female plants will be producing sticky, THC-laden buds, that, if fertilized, the THC loses potency.

If you spot a male flower characterized either by their clearly male pollen sacs, or their yellow banana-like shape, remove the entire bud site to ensure no pollen escapes. Just one could fertilize your entire crop.

Why does this matter?

Unfertilized buds (“sinsemilla”) are highly valued by many marijuana users. These buds are more potent because a fertilized female stops focusing its resources on growing its buds and will grow seeds instead.

An unfertilized female plant, on the other hand, will produce more THC than any other variety of plant. This is simply because it focuses more of its attention on growth rather than reproduction.

Males also produce THC, but at a much smaller volume than the females. Therefore, if you want to grow the most potent buds, pay attention to the sex of your plants and keep your females unfertilized.

Conditions in Your Grow Room

Indoor growers have unique challenges once the flowering stage is under way. Now that your marijuana plants have grown larger (and extremely close to each other), they need a different environment to say healthy. You’ll want to adjust the air temperature, and humidity in your grow room to prevent disease and encourage growth.

When there is light, keep temperatures between 68ºF and 77ºF (20ºC and 25ºC) near the foliage and 68ºF (18ºC) at the roots. Remember, higher temperatures require accordingly higher levels of carbon dioxide. In darkness, you can let the temperature drop down to about 68ºF (18 degrees Celsius).

At the beginning of the flowering stage, lower the humidity to around 40-50%. You can drop it to 30% or more the second month to force the buds to produce more resin. This is lower than what was needed during the vegetative stage, and it is essential to the success of your plants when growing indoors. The humidity must remain below 50% during the flowering stage, so use a dehumidifier if necessary.

Signs of a problem

Remember those yellow leaves we mentioned earlier? A few are okay, but too many in your indoor setup might indicate a serious problem. Excessive leaf yellowing could be a sign of a nutrient problem or light burn – and both are easy to do during the flowering stage.

Another sign of light burn is foxtailing. This is when a new bud (called a spire) emerges out of the side of an old bud. If you see this, it’s not normal, and it’s not good. It means the heat or light in your grow room is wrong. Improper conditions like this can discolor your buds and possibly evaporate your THC.

Pruning Your Plants

Prune your plants during the second month of the flowering stage . You should have finished any low-stress training, and your plants would have stabilized their growth patterns. Some growers still try super cropping at this point, but it is not recommended because many plants will not have enough time to recover from the stress.

The best growers know how to prune their plants.

It’s not necessary, but some growers prefer to do it to optimize their plant’s growth. This is because it saves the plant energy and helps ensure that the majority of light and nutrients goes to the most promising buds.

How do you prune?

• Remove leaves that will not thrive
• It’s okay to prune any of the buds that are in the shadows
• Do not prune leaves that are in the shadows but are still thriving

You shouldn’t prune too many leaves because your plant isn’t going to grow many of those leaves back. Plus, you need them to absorb light and keep flowers developing.

Trimming your leaves

Trimming and pruning are two different things.

Discolored leaves can be trimmed. As leaves turn yellow, you can remove them. They’re yellow because they are not thriving and energy is being devoted to the flowering parts of the plant. Just make sure you don’t remove any green leaves— those are still producing valuable energy!

What about defoliation?

Some growers practice defoliation by removing some of the leaves off a plant to expose buds to more sun. However this is a risky thing to do.

The leaves are what helps the plant mature, and even if a leaf is blocking your flowers from direct light, chances are, they’re still doing their job. A healthy leaf protects the health of an entire plant, so unless the leaf is dying or dead, leave it alone and let it do its job.

Watch those pH levels

Flowering plants are sensitive, and one issue that can be easily overlooked is pH. Many marijuana plants suffer from incorrect pH levels, specifically in the root area, and it can be fatal.

Monitoring the pH level is essential regardless of your growing medium or setup. Signs of a pH problem include wrinkled or curled leaves or what may be mistaken as a nutrient deficiency.

Whenever there is a problem, always start by checking the pH levels near the roots to see if that is what’s causing the issue. In soil, the pH level should be between 6.0 and 7.0. In hydroponic systems, it should be between 5.5 and 6.5.

PH testing is useful at every stage of growing, and should not be overlooked during the flowering stage. The good news is that testing pH levels is quite easy and inexpensive. Regardless of where your plants are in their growing progress, you should buy yourself a pH testing kit.

Preventing Nutrient Burn

PH isn’t the only thing to be concerned about.

Nutrient burn can also impact your plants during the flowering stage as your plants are very sensitive to any errors at this point. Regardless of the type nutrients you use, whether it be organic compost or store-bought chemicals, you have to be careful not to overdo it.

Too many nutrients can burn your plants and cause an unpleasant taste. Plus, during the last few weeks of flowering, there isn’t enough time to repair the damage.

Nutrient burn will cause the tips of your plants to look burnt. Some signs of it, especially in the beginning parts of the flowering stage is okay, but if the burn begins to show in the “fingers” of the leaves, you’ve gone too far.

What should you do?

The best way to reduce this risk is to limit nutrient use to only when there is a clear nutrient deficiency. Then, introduce nutrients gradually. You’ll also want to check the pH first, to make sure that the issue isn’t actually related to pH instead of nutrients.

The Final Weeks of Flowering

Wondering if you are done yet?

The flowering process generally takes about 1 to 2 months, but you may find that some strains go an additional two weeks. Because there is no set number of weeks for flowering, you must be prepared to recognize the signs.

Tip: make sure to download my free Grow Bible for more information

Maturity is the most sought-after stage in the cannabis life cycle. When you’ve reached this point, you’re just days away from being able to harvest.

So, are you done?

You will know that the plant is ready to harvest because the calyces and pistils will swell up and start to turn red. The resin continues to accumulate, getting stickier and heavier with every passing day. The flowers draw together and close up any remaining space.

The final weeks will bring about a considerable increase in THC production on or around the buds. This is actually a great thing for your plants (and you, of course) because THC is a mild, natural pest deterrent to keep any bugs away from the flowering plant. This is one reason why THC has such a powerful odor.

Here’s a tip:

If you aren’t already using carbon filters, now is the time to do so. You won’t be able to mask that smell.

Preparing Your Plants for Harvest

A vital thing to remember — for your own health, as well as the quality of your buds — is to flush out your growing medium between 1-2 weeks before you harvest.

Plants need this process to irrigate and rinse minerals and nutrients out so that it is safe and enjoyable for use. You want to completely remove the nutrients you have been feeding your plants — whether chemical or organic — so that none of it remains in the consumable product at the end.

Generally, this should happen about two weeks before the flowering stage ends (in the second month of flowering), but it could vary by the medium used. Rock wool, soil, and coconut fiber require two weeks, but if you’re using clay pellets, even a week of water rinsing will clean out the substrate.

Here’s how to flush your plants:

• Use neutralized water (water with a balanced pH level)
• Test the water before giving it to your plants
• Water your plants with this water

This water can also help in the case of a pH imbalance in the soil, or if you have a nutrient toxicity issue.

Know When to Harvest

When you harvest will have a huge effect on the end product. While the actual timeframe depends upon the strain, desired results, and your own personal preferences, most strains are ready to harvest after a two to four-month growing cycle.

For a more energetic high, harvest on the earlier side. For a relaxed high with that classic couchlock feeling, harvest a bit later. Just don’t harvest too late or too early, or you may end up with too subtle of an effect or a type of high that is undesirable.

A quick guide to harvesting

Generally speaking, when at least half of the pistils on the plant are red, you are ready to harvest.

Here are some more signs:

• Resin that is thick, and easily visible to the naked eye
• A plant that is very heavy with buds, with some of the leaves turning yellow.
• Trichomes that are mostly white and milky, as can be seen with a microscope or magnifying glass.

Patience is key to timing the harvest right.

Sometimes harvesting needs to happen a little earlier than planned, especially if your plant is unhealthy. If your buds look burnt or discolored, or you’re leaves are showing signs of disease, and it is getting worse, it may be better to harvest a little early. If you do need to harvest your plants early and it impacts the quality, sometimes curing can fix it.

Go here to learn more about curing marijuana

As you can see, the flowering stage is an exciting period in the marijuana life cycle that leads to everyone’s favorite time – harvest. By paying careful attention to your plants and getting plenty of practice, you can learn to grow the most potent, highest yielding marijuana around.

Happy growing!

Frequently Asked Questions

Why do indoor plants need total darkness to prevent flowering? Marijuana is sensitive to certain light spectrums. Indoor lighting includes spectrums that could stimulate flowering, while spectrums produced by the moon do not. For more on light spectrums read this article.

How do you know when to start flowering? How long your plants remain in the vegetative stage is up to you. However, you should keep in mind that they will grow even larger during the flowering stage, so make sure you have space.  For more on the vegetative stage, read this article.

How long can you use nutrients? Nutrients can be used throughout the grow cycle, which ends about two weeks before they are ready to harvest. About two weeks prior to harvest, you should stop adding nutrients and possibly flush your plants. Learn more about nutrients in this article.

The founder of I Love Growing Marijuana, Robert Bergman, is a marijuana growing expert that enjoys sharing his knowledge with the world. He combines years of experience, ranging from small-scale grows to massive operations, with a passion for growing. His articles include tutorials on growing... [read more]

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