The flowering stage is the ultimate phase as plants transition from vegetative growth to producing buds. This period requires attention due to bud formation, strong aromas, and high nutrient demand. This week by week guide explains the process of adjusting light schedules and nutrients, and vigilant pest control, working towards a successful harvest.
Now that your plants have a proper foundation, it’s time to start flowering. This is the most fun part of growing and where all the prep work you’ve been doing will start to pay off. Plants in the flowering stage (or bloom phase, or bloom stage), require more regular maintenance than vegetating ones, so be sure to plan your schedule accordingly. It’s best to avoid any vacations during this period.
What is the flowering stage?
As the name suggests, this is the part of the plant’s lifecycle where it begins producing the flowers that we’re all looking for. The flowering phase of cannabis is characterized by explosive growth, pungent smells, and heavy nutrient consumption so make sure that you’ve got everything ready before you pull the trigger.
Broadly speaking, the flowering stage consists of two smaller stages: pre-flowering and flowering. While they both count as “flowering” knowing what stage you’re at is essential for proper nutrient and time management.
Pre-flowering
This is the transitional phase between vegetating and flowering. During pre-flowering, cannabis plants will begin showing the very first signs of flowers. The pre-flowering period can last from 1-3 weeks depending on the strain, but the first signs should become apparent in a matter of days.
This is the time when you’ll start seeing the first signs of flowers, making it possible for growers to separate the males from the females. Most of us are growing for flowers, not seeds, so getting rid of any male plants before they’ve had a chance to pollinate the females is a must.
Note that if you’re using feminized seeds, then you can expect over 90% of the seeds to be female, but it’s always important to check your plants early and often at this stage. Female grants should grow fine white hairs called “pistils”. These are the same white or orange hairs that you’ll commonly find on almost any buds. On the other hand, male plants will develop small pollen sacks that are rounder and hairless.
You’ll begin to notice an increase in plant growth and the tops of the plant should take on a brighter green colour before growing the first white hairs. These areas are where the future colas will form.
Flowering
This is where the real magic happens. Over the course of the next several weeks, those white pistils will rapidly multiply and then begin growing into proper flowers. This is the final stage in the lifecycle of cannabis plants and is also when they are most vulnerable to infestations and diseases.
The flowers of cannabis plants are popular homes for many types of bugs and keeping your plants clean is paramount to a successful harvest. Check out our guide on spotting and eliminating the most common pests for more information.
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When should I start flowering my cannabis plants?
While this is a straightforward question, it doesn’t have a straightforward answer. Several factors need to be considered when you’re deciding to flip your plants to flowering.
Photoperiod seeds
As with almost everything else, it depends. The first thing to keep in mind is your space; plants can easily double (or even triple) in height during flowering.
For example, let’s say that your grow space is 2 meters tall, and your plants are starting at 30 cm off the ground. Additionally, your light will need a minimum of 30 cm of space at the top. This gives you an effective vertical space of 140 cm to grow your plant. In this case, you should flower your plants at around the 40-50 cm mark.
This, of course, assumes that you’re not using any sort of training techniques and is meant to serve as a baseline. If you’re interested in more advanced growing techniques to maximise your space, take a look at our grow guides.
Keep in mind that flowering sooner is almost always better than later if you’re concerned about space. A short plant is a mild disappointment. A plant that’s too tall can be a complete disaster. Consult the strain’s fact sheet for info, but keep in mind that the numbers there are averages and your plants may behave differently.
It’s also worth noting that if you’re growing outdoors, you have no control over when your plants start flowering. Outdoor plants will start flowering according to the season and your specific latitude. Once there are less than 12 hours of daylight, they’ll switch to flowering. While it’s possible to use supplemental lighting in something like a greenhouse, it’s not typically done.
Autoflowering seeds
If you’re using autoflowering seeds, then there’s nothing that you need to (or even can) do. These seeds will automatically flower (hence the name) after a predetermined amount of time. This makes them generally faster than photoperiod strains at the cost of being less variable.
You’ll know that your autoflowering plants have begun to flower when they enter the pre-flowering stage described above.
How do I start flowering cannabis plants?
Once it’s time to start flowering, the process is as easy as 123.
- Adjust your lights
Photoperiod plants, as the name suggests, require a certain ratio of light to darkness to begin flowering. If you’re ready to start flowering your plant, all you need to do is switch the lights to a 12-hours-on-12-hours-off schedule. Don’t try to do this manually every day, get a timer.
- Adjust your nutrients
Plants require different nutrient levels at different stages of growth. Any pre-mixed nutrients will come in a “grow” or “vegetating” mixture as well as a “bloom” or “flowering” mixture. Consult the label and follow the instructions as closely as possible, don’t just try to eyeball it.
- Prune excess vegetation
By now, you should’ve already pruned your plant at least a few times but this is always a great time to do it again. By picking which branches to keep, you get complete control over where your plant flowers meaning that you can maximise the amount of light and air that your flowers receive.
Once you’ve done these, all that’s left to do is watch and wait for the first flowers to appear.
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How long does flowering last?
There’s no really good answer to this. Basically, you can’t rush nature and the plant is ready when it’s ready. Typically, this takes anywhere from 8-12 weeks, though some strains can be faster or shorter. Even different plants of the same strain may have flowering times that can be weeks apart.
On the whole, sativas tend to take longer than indicas to finish blooming. If speed is your top priority, then strains like Top 44, Bubblegum XXL, or WSS Skunk are all good fast-flowering choices.
With that said, every plant follows (roughly) the same pattern of development during the flowering phase, just at slightly different speeds.
Flowering stage by week
Once the pre-flowering stage has ended and the plants begin to properly bloom, you can expect them to follow these steps.
Week 1-2
As mentioned above, be ready for your plants to undergo rapid growth over the first few weeks. Cannabis plants will usually at least double in height after the switch to flowering and that starts almost immediately. On average, a plant will experience about 2/3s of its total growth in the flowering phase so be sure to start flowering well before you think you’ll need to.
Within a week, you should begin seeing the very first signs of flowering. These first changes will be the aforementioned growth of pistils at the joints where fan leaves meet the stem (the area known as a “calyx”) and these “pre-flowers” are a sign that everything is going smoothly.
Within the next week or so, you should begin seeing groups of single leaves sprouting out of the tops of your main colas and white pistils will start coming out of the middle of these. These sites will form your main buds. By now, your plants should begin to give off that distinctive odor so make sure that your area is properly ventilated.
As the second week rolls around, the growth of pistils should be accelerating rapidly and new growth should be visible every day. By now, the flowers should also begin to produce the trichomes (crystals on the flowers) that will eventually hold the THC that we’re looking for. These should begin to appear on the flower sites and adjacent leaves.
Weeks 3-5
Over the next few weeks, the plant is in full bloom and the flowers will become noticeably larger and denser every day. During this time, the plant’s recent rapid vertical growth should be slowing down, though it is likely to continue for another few weeks.
This is a fairly vulnerable time for the plant and any stress or damage now could seriously impact your final harvest. This is when any nutrient deficiencies will start to become incredibly noticeable and these need to be addressed immediately. Check out our guide to diagnosing common issues with cannabis plants to learn more about dealing with these issues.
If your plant is still looking healthy and growing normally, then there isn’t anything more to do that you haven’t already been doing. This is also the last real chance that you’ll have to remove any excess leaves or unwanted flowering sites, so try to get in one final trim before entering the final stretch. Just try not to go overboard, your plant won’t be regrowing much new vegetation at this point.
Weeks 6-8
Over the next few weeks, you’ll be increasingly tempted to harvest your plant but patience is a virtue. Even if the flowers have stopped growing noticeably larger, they are still growing. During this phase, the buds are becoming denser and heavier while also producing even more trichomes.
At this point, many leaves will have likely begun to turn brown and brittle. This is perfectly normal and is a sign that the plant is putting all of its energy into growing flowers. Your plant should have stopped growing any new vegetation and should be at a consistent height.
Getting into the 7th or 8th week, most plants are getting ready to be harvested. While there’s no single rule for the “ideal” time to cut your plant down, a good indicator is when the trichomes begin to turn from clear to amber. Once about 50-60% of these have changed, it’s time to enter the final stage of flowering.
This is the single most important phase of your plant’s entire life so make it a priority. If you’re planning any holidays or extended absences, try to make sure that they don’t overlap with this stage. While a plant can be left alone for a day or two, if anything goes wrong (light goes out, runs out of water, nutrient deficiency, pest infestation, etc.) and isn’t corrected immediately, the plant will almost certainly suffer and could even die.
Weeks 9+
If your plant is getting close to harvest, it’s time to flush (or leech) it. To do this, simply start giving it pure, clean water with no nutrients. This will allow it to use up any remaining chemicals that may be present ensuring that you get only the freshest and cleanest taste from your buds.
If your plant still doesn’t seem ready after 9 or 10 weeks, give it another week. Sometimes, they just need a little extra time. Some strains (like Super Silver Cheese or Gorilla Haze) have exceptionally long flowering times and can often require as much as 90 days to finish ripening. Before you plant your seeds, always make sure that you can commit as much time as necessary to finish the job.
When should I harvest my plants?
These last few weeks are typically the most stressful for the grower and the most important for the plant. Many novice growers (and even seasoned pros) can get a little too excited and harvest too soon.
Different strains flower at different speeds but the 7-10 week range is most common. During this time, keep a close eye on your plants to make sure that you harvest them at the right time. The main things to look for are the leaves, pistils, and trichomes.
- Leaves
As mentioned, the fan leaves of a plant turning brown can be a sign that it’s nearly time to harvest. It’s important to keep in mind, however, that this can also be a sign of an unhealthy plant, so pay attention. If this is happening after only 2-3 weeks, something’s wrong, but if it’s happening after 7-8, then it’s probably fine.
- Pistils
The white hairs on your flowers will (most likely) eventually turn an orange colour. This signifies that the plant is getting near the end of its flowering phase and that you should consider harvesting soon. This isn’t the best indicator overall, as many strains do not change their pistil colour much or do so after the ideal time to harvest.
- Trichomes
This is probably the most consistent way to evaluate a plant’s readiness. These crystals are where the THC is produced and stored and as they mature, the chemical nature of the plants changes. Generally, once these are 60-70% amber, it’s time to cut the plant down.
These are just general guidelines. For more details, be sure to read our guide on the best time to harvest your plant.
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How do I take care of flowering plants?
Taking care of flowering cannabis plants requires dedication, finesse, and a watchful eye. While it’s possible to grow and harvest weed with the bare minimum effort, you’ll also get the bare minimum quality and quantity. Taking the time to properly care for your plants is a must.
The single most important thing that you as a grower can do for your plants is to give them the best possible environment.
Light
The more light you give your plants, the more productive it will be—within limits. The old idea that you can’t give a plant too much light is only partially true and going overboard can harm your plants. While this might seem counter-intuitive, it makes sense when you consider how plants grow in the wild.
Many growers want to keep their plants under as much light as possible for as much time as possible and, generally speaking, this is a good idea. But, you do need to be aware of the fact that a plant can absolutely get too much light. Outdoors, plants have nighttime darkness and cloudy days to regulate their photosynthesis; indoors, there’s no such restriction.
Plants use sunlight to absorb and process nutrients. By giving them too much light, they can uptake more nutrients than they can process leading to nutrient burn. This is why most growers keep even vegetating plants under only 18 hours of light (as well as huge savings on energy costs).
But during flowering, the risk of too much light is still there. As a general rule, you want a maximum of 1000 µmol/m²/s (micromoles per square meter per second) over a single square meter of grow space. Most lights sold for growing have this information displayed on the website or packaging, so that’s a good place to start.
It’s also important to keep in mind that not every leaf is equally valuable on a flowering plant. If a leaf isn’t getting light, it’s not producing anything the plant can use and is just a drain on resources. For LED lights, only the top 3-5 layers of leaves will get any useful light.
Humidity
While seedlings might require humidity of up to 70%, flowering plants need it much lower. Typically, plants during flowering should be kept at around 45% humidity to minimise the risk of mould or algae.
Cannabis buds are damp and sticky and provide an excellent home for all manner of moulds. Additionally, large plants put a tremendous amount of moisture into the air through a process called transpiration. If your humidity is above 50%, you may want to consider more powerful ventilation or even a dehumidifier.
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Airflow
External ventilation is a must for both climate and odour control, but internal airflow is also a must. While internal fans during vegetation help to strengthen the plant, these same fans during flowering can help keep the buds dry. Likewise, moving air makes it harder for flying insects to manoeuvre, keeping them off of your plants.
Space
Make sure that your plants have enough space horizontally as well as vertically. Plants seem to know when they bump up against another plant and tend to compensate by growing up instead of out. If you’re already working with limited height, this can be a major issue. Overall, it’s best to give your plants more space than you think they’ll need.
Support
As your plants continue to grow bigger, heavier buds, they can run the risk of snapping under their own weight. Wooden dowels are a great choice for providing a little extra support to your plants to make sure that they stay upright.
Harvesting a cannabis plant
Now that your plant is ready, it’s time to harvest. There are several ways to harvest a plant and every grower will slowly develop a strategy that works best for them. The simplest method is to just cut it down, remove the fan leaves, and hang it upside-down in a dark room for 10-14 days.
Once the branches snap when bent, you can trim up the flowers, put them in a glass jar, and begin the curing process. This can take up to 6 weeks and is the single most important step in creating a tasty and smokable final product. For more information, read our complete guide on harvesting and curing.
Growing cannabis is one of the most rewarding hobbies out there, but it requires some serious commitment. When it comes to growing, there’s a huge gap between just doing it and doing it well. By following the steps outlined, you’ll be well on your way to a successful harvest.
