Flowering Stage

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 during this phase, 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. Since you’ve already invested so much time and effort into your plants, it would be horrible to ruin the harvest this late in the game.

This guide will explain each exciting milestone, teach you what to expect, and provide tips on how to optimize this time to produce the most potent buds and highest possible yields.

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.

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.

‘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 the 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, the date your plants will flower depends on the time of the year and your location. Some strains may start the flowering stage before others, 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.

Once the flowering stage has begun, the internodes (those spaces between the leaves) decrease, and the plant’s growth slows down, although it will continue to grow upwards. It may seem like your plant isn’t growing anymore, 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 your plants outdoors, the flowering stage will begin naturally, but sometimes there are situations where you might want to induce flowering. 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.

In an indoor setup, the flowering stage will not begin naturally. Since you are providing sunlight via artificial lights, simply 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. Make sure 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 they may 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 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. 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

In the first month of the flowering stage, you will 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 start seeing that it is no longer producing leaves, but instead, small white pistils are beginning to grow rapidly along the surface of the plant. You’ll also start to notice flowers growing on the buds.

Now is the time to pay special attention to these flowers, because this is when your plants will start to clearly reveal their sex. During this time, males create a pollen sack in preparation for flowering. Females, on the other hand, 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 into the female pistils.

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, 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.

In addition to the emergence of flowers, you’ll also notice that the internodes have extended and that some leaves are 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.

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 time to harvest.

Nutrients during the beginning of the flowering stage

When your plants begin the flowering stage, they will need a different set of nutrients then earlier in their life. 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

The flowering stage is hard on marijuana plants. Your plants are going to be very sensitive to both their nutrients and the environment, so it is imperative to keep an eye on your plants. Pest and diseases could be fatal at this point, and there’s still at least a month to go. 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 are using 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. Flowering formulas are designed to meet the high demands of this portion of the growing cycle, but vegetative formulas will make sure that your plants have the nutrients that they need to flower successfully. If you decide to use nutrients, stick to using them in the first month, if possible. Nutrients should not be used in the final weeks of flowering.

As the flowering stage continues, you may notice that your plants begin to lose a few leaves, but this should only be 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 beginning 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. Training helps maximize the space in a grow room, and it can also increase your final yield. When stems are still young, they can respond to training. During the beginning of the flowering stage, the stems are flexible and can be bent without breaking, but 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. 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.

The second month is an exciting time for growers because this 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.

All this growth can lead to problems however 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! 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.

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

During the second month of flowering, you want to make sure your plants are getting plenty of circulation. This is particularly important when growing indoors. Because the plants grow so wide during this period, 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 from your crop before the flowering stage began, but that doesn’t mean you are necessarily out of the water. Unfortunately, it is not uncommon for a hermaphrodite to develop during the flowering stage. These sneaky plants have male sex organs that will pollinate your precious female plants, so checking again during the flowering stage is always a good idea.

By the second month of the flowering phase, if you have any males in your garden, it’s almost too late. At this point, the female plants will be producing sticky, THC-laden buds and if they are fertilized, the THC will not be as potent. If you spot a male flower — characterized either by their clearly male pollen sacs, or the yellow banana-like shape –, you should remove the entire site of the bud to ensure that no pollen escapes. Just one could fertilize your entire crop.

Unfertilized buds (known as “sinsemilla”) are highly valued by many marijuana users. These buds more potent because a fertilized female plant will stop 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 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 some unique challenges once the flowering stage is well 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 plants are exposed to light, keep the temperature between 68ºF and 77ºF (20ºC and 25ºC) near the foliage and 68ºF (18ºC) at the roots. Remember that higher temperatures will require accordingly higher levels of carbon dioxide. When your plant is in darkness, you can let the temperature drop down to about 68ºF (18 degrees Celsius).

At the beginning of the flowering stage, you should lower the humidity to around 40-50%. In the second month, you can drop it to 30% or more 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.

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

The second month of the flowering stage is when you should prune your plants. 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.

Pruning is not necessary, but some growers prefer to do it to optimize their plant’s growth. Pruning saves the plant energy. It helps ensure that the majority of light and nutrients goes to the most promising buds – meaning those that will not thrive can be removed. You can prune any of the buds that are in the shadows, but not the leaves. Your plant isn’t going to grow many of those leaves back, and you need them to absorb light and keep flowers developing.

Discolored leaves are another issue. 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!

Some growers practice defoliation, removing some of the leaves off a plant to expose buds to more sun, but it 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

Nutrient burn is a serious concern 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 overdose your plants on nutrients. 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. The best way to reduce this risk is to limit nutrient use to only when there is a clear nutrient deficiency, and 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

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 know when the process is done.

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. 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 will continue to accumulate, getting stickier and heavier with every passing day. The flowers will 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. 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.

Flush your plant’s system by using neutralized water, (meaning it has a balanced pH level). Test it before giving it to your plants. 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

The time 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.

Generally speaking, when at least half of the pistils on the plant are red, you are ready to harvest. The resin should be thick, and easily visible to the naked eye. The plant should be very heavy with buds, and some of the leaves might be turning yellow. Do not harvest until the pistils are at least half (preferably more) darkened, or when the trichomes are mostly white and milky, as can be seen with a microscope or magnifying glass. Patience is key when 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!

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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