The flowering stage is the most eagerly awaited moment on a cannabis grower’s calendar. Learn how to master this crucial stage of your plants’ lives by providing them with the right conditions, nutrients, and more. Trust us, it’s worth it – you’ll be reeling in heavy harvests of potent, delicious flower in no time.
Rather than focus on the growth of healthy foliage and strong roots, flowering cannabis plants focus almost exclusively on the development of their buds. In turn, blooming females have unique needs and prefer different conditions than vegetative plants. As a grower, it is your job to meet those needs so your plants can produce the best possible flower. Luckily, that’s exactly what you’ll learn here.
From nutrients to lighting and everything in between, keep reading for an in-depth walkthrough of the cannabis flowering phase and how to master it.
Cannabis flowering 101 – The basics of when, how, and why weed plants flower
Before we get stuck into the nitty-gritty details of how to care for flowering weed plants, it helps to have a basic understanding of when, why, and how female cannabis plants produce their sought-after buds.
Out in nature, female cannabis plants belonging to the indica and sativa species typically start flowering after the summer solstice when daylight hours gradually decrease, signalling the coming of winter and the end of cannabis’ natural growing season. Ruderalis plants, on the other hand, flower automatically after a few weeks of vegetative growth – a trait the species likely developed in response to the short summers of its native habitat.
After sprouting, cannabis seeds enter the seedling stage – a fragile state during which they focus mainly on the development of strong roots. After the seedling phase, cannabis plants enter the vegetative stage, where they focus on developing green growth to soak up the sun before entering the flowering phase – the last stage in the cannabis lifecycle.
In the weeks prior to flowering, cannabis plants produce preflowers which growers use to identify the sex of their plants – a crucial step in growing potent sinsemilla weed. As they approach the flowering phase, female cannabis plants also tend to stretch as they prepare to bear the weight of their flowers.
Budding female cannabis plants focus most of their energy on developing flowers designed to catch airborne pollen released by nearby male plants. Once pollinated, a female weed plant will then shift its focus to developing healthy seeds that are eventually released into the ground when the plant dies, birthing a new generation of plants in spring.
When growing cannabis at home, you’ll want to cull any male plants as soon as possible to keep them from pollinating your females. Over time, this will encourage your plants to produce larger flowers packed with aromatic and potent resin. This method of growing, known as “sinsemilla” was discovered and promoted by the drug trafficker Rafael Caro Quintero in the 1970s in Sinaloa, Mexico.
When will cannabis flower outdoors?
If you’re growing photoperiod cannabis strains outside, they’ll usually begin transitioning into the flowering phase after the summer solstice – between June 20th-22nd in the Northern Hemisphere, and around December 20th-22nd in the Southern Hemisphere.
While every strain is different, you should see notable signs of flowering in your outdoor cannabis plants by the end of summer.
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When will cannabis flower indoors?
Indoors, photoperiod cannabis plants will begin flowering once you reduce their daylight hours. Most growers do this by moving from an 18/6 light-dark cycle for veg to a 12/12 cycle for flowering.
After flipping your plants into bloom indoors, you should notice notable signs of flowering within 2-3 weeks.
What about autoflowers/automatic strains?
If you’re growing autoflowering cannabis, your plants will start flowering naturally 3-6 weeks after germination. Autoflowering cannabis strains flower independently of their light cycle, so most growers cultivate them under 18-20hrs of light per day to maximise their growth and yields.
How long does the cannabis flowering phase last?
Indoors, most cannabis strains can be harvested after 8-10 weeks of bloom time. Outdoors, on the other hand, most cannabis strains will be harvest ready by October in the Northern Hemisphere and April in the south. However, remember that every cannabis strain is unique – some strains (particularly indica varieties) may be ready to harvest a little earlier, while some sativas can take significantly longer.
Note: Never harvest your cannabis simply based on how many weeks it’s spent in bloom. Instead, carefully inspect your plants’ flowers to ensure you harvest them at their peak ripeness. Learn how to distinguish overripe and underripe cannabis flowers here.
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What conditions are best for flowering cannabis plants?
Flowering cannabis plants have much different needs to vegetative plants. Whereas vegging plants generally thrive in warm, humid conditions and rely heavily on nutrients that stimulate the growth of roots and foliage, flowering plants generally prefer slightly cooler conditions and different nutrients.
Again, every cannabis strain is different, and you’ll become more refined at understanding the needs of different plants as you gain more experience cultivating different varieties of cannabis. In general, however, flowering cannabis plants like:
1. Less light
Photoperiod cannabis plants need to perceive a drop in daylight hours in order to flower. Outdoors, this happens naturally after the summer solstice (as described above). Indoor growers, however, need to emulate this by reducing the light hours in their tent or room from 18 to 12 hrs per day. Note that flowering cannabis plants also need complete darkness – light leaks can cause them to revert back to veg.
2. Cooler, dryer conditions
Most flowering cannabis plants grow best in daytime temperatures of 20-24°C (65-75°F); nighttime temps of 18-21°C (65- 70F), and relative humidity of around 55%.
3. Good ventilation
Your grow space should always have a light breeze, as this promotes even temperatures and humidity while also repelling pests and pathogens that thrive in hot, humid conditions. When using oscillating fans, it can help to install fans both above and beneath your canopy. Never point your fans directly at your plants as this can stress them.
4. Light nutrients
Overfeeding cannabis plants is always troubling, but the stress it causes can be particularly detrimental to flowering weed plants, causing stunted growth or even triggering hermaphroditism. To avoid these issues, feed your plants sparingly and using bloom-specific fertilisers predominantly rich in phosphorus, potassium, and light micronutrients.
5. The right pH
Whereas vegetative cannabis plants prefer a pH of 6-7, flowering plants benefit from a slightly higher pH of 6.5-7.5 as it favours the uptake of nutrients needed for flower production.
6. Protection
If you’re growing outdoors, consider bringing your flowering plants under cover during strong storms or heavy rain. Weather damage causes stress, and rain can cause mould in dense flowers, especially during the final stages of flowering.
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What nutrients do flowering cannabis plants need?
Whereas vegging cannabis plants rely heavily on nitrogen (N) to fuel the growth of their leaves and branches, flowering plants prefer different fertiliser. Ideally, you’ll want to gradually increase the amount of phosphorus (P) and potassium (K) you feed your plants while simultaneously providing them with ever less nitrogen. Using specific cannabis fertiliser kits and following a feeding calendar can help simplify this process for beginners.
For optimal bud growth, cannabis plants also need minor concentrations of secondary nutrients like magnesium (Mg), calcium (Ca), sulphur (S), zinc (Zn), manganese (Mn), iron (Fe), boron (B), and more. You can use molasses liberally throughout the final weeks of flowering to help boost your plants’ resin production as well.
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How often should you water flowering weed plants?
There is no one-size-fits-all approach to watering cannabis plants, though it is true that budding plants usually need less water than vegging plants. Just like during the veg phase, you should only water your cannabis plants when their soil is dry to the touch. Stick your finger 2 centimetres deep into your plants’ topsoil, and water them when it feels dry.
What does the cannabis flowering stage look like?
Weeks 1-3 of flowering:
Don’t expect sudden changes after the summer solstice or immediately after you start reducing the light hours in your grow room. Your plants won’t stop growing and start flowering from one day to the next – the process is much more gradual.
The biggest change you’ll notice in your plants in their early days of flowering is their height. Most cannabis plants stretch once they transition into bloom, sometimes doubling or tripling in size. Indicas typically stretch less, while sativas are known to stretch considerably.
You may also notice your plants developing new leaves, particularly around the top of their canopy. To fuel this growth, your plants will require some nitrogen and other grow nutrients, so it’s a good idea to keep an eye on them and feed them lightly during the first week of bloom if necessary.
After 2 weeks in bloom, you may see your plants developing pre-flowers. This is the time to “sex” your plants and separate/cull any males to keep them from pollinating your females. Learn how to properly sex your cannabis plants here. During this second week, you should also consult your feeding calendar as most fertiliser manufacturers recommend switching to bloom fertilisers around this time.
By week 3 of bloom, your plants will generally have stopped stretching. They may also be showing the first signs of growth at their bud sites. By this time, your plants will begin focusing almost entirely on the development of their flowers, so it’s important you support them with the right nutrients.
Weeks 4-6 of flowering:
This is the mid-flowering phase, during which you’ll see your plants’ flowers take on some serious weight. You should notice your buds develop thick stacks of calyxes with milky white pistils and evermore resin. Your plants will develop a strong odour during this time, which you might want to tame with a carbon filter.
By week 5 of bloom, your cannabis plants should be fairly heavy with flowers. They may also start developing some amber pistils – a sign that they are maturing nicely.
Weeks 6-10+ of flowering:
This is the late flowering phase. During this time, your plants should continue developing fatter flowers with darker pistils and trichomes, indicating that they are edging ever closer to their peak harvest date. Their aromas should also become much more intense during these final weeks.
While every strain is different, most modern cannabis hybrids will be ready to harvest after 8-10 weeks of bloom time indoors. Some fast-flowering strains may be ready a little earlier, while some sativas can take 12 or even 14 weeks to fully mature.
Hindu Kush and Northern Lights, for example, are both fast-flowering strains that can be harvest-ready after just 6-7 weeks in bloom. Strains like Big Bud and Ed Rosenthal Super Bud, on the other hand, take around 8-10 weeks to flower, while Amnesia White and Silver Haze are long-flowering plants that can take over 12 weeks to reach their peak maturity.
During the final weeks of flowering, it’s vital to keep tabs on the humidity in your grow room. Overly humid conditions can cause moisture to be trapped in your buds, which can lead to bud rot and other issues. You’ll also want to flush your plants during this time to ensure a smooth, clean smoke.
Note: This is a general overview of what to expect during the different weeks of flowering. Remember that every cannabis plant and growing environment is unique, and therefore you may see slightly different results in your grow room/garden, especially if you’re growing cannabis outdoors.
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Tips for mastering the flowering phase:
Now that you have a basic idea of what to expect during the cannabis flowering phase, it’s time to learn how to care for your plants properly during this crucial time. To do this, we recommend doing as much prep work before your plants begin flowering so that you’re not left addressing issues on the fly.
Before flowering, remember to:
- Trim and defoliate your plants. This will help remove excess foliage and ensure enough light penetrates your canopy, resulting in better bud growth all across your plants. Moreover, removing lower branches and bud sites can help channel your plants’ limited energy towards their higher bud sites which will naturally produce thicker, heavier, and more potent flowers.
- Ensure your plants are in their final containers. Ideally, you’ll want to give your plants at least 2 weeks to recover from their last transplant before switching them to bloom. If you’re growing outdoors, consider moving your plants into their final containers before the summer solstice.
- Address any minor issues before moving into bloom. If you’re growing cannabis indoors, you have the advantage of being in full control of when your plants begin flowering. Use this to your advantage, and only flip your plants once you’re certain that they are 100% healthy. If you ran into issues such as over/underwatering, nutrient burn/deficiencies, or pests during the vegetative phase, address these problems and give your plants at least 1-2 weeks to recover from any resulting stress before flipping them to bloom.
- Apply training. Most training methods will cause your plants some stress and should be performed well before your plants start flowering. LST, Topping, FIMing, Lollipopping, and Mainlining are just some examples of very effective training techniques you should employ before flipping your plants.
- Consider building a trellis or screen to help support your plants as their branches grow heavy with buds.
- Check for light leaks. Light leaks can stress flowering plants, either keeping them from flowering altogether, reverting them back to their vegetative phase, or even triggering hermaphroditism. Meticulously check for light leaks in both indoor and outdoor gardens and address them before your plants enter bloom.
- Begin acclimatising your plants to their flowering conditions gradually. Again, if you’re growing weed indoors, use that to your advantage. Rather than abruptly changing the lighting, humidity, and temperature in your grow space, give your plants time to adjust to these new conditions by keeping them in veg for a few extra days while you gradually tweak their environment.
- Provide your plants with extra space. Keep in mind that your plants will stretch considerably once they enter their bloom phase. Providing them with space early on will prevent your plants from growing too closely together, which helps to prevent the buildup of hot, stale, humid air pockets around your room/tent/garden.
During flowering:
- Remember to keep close tabs on the temperature and relative humidity throughout your grow room at all times.
- Gradually introduce your plants to their bloom fertiliser during the first 1-3 weeks of flowering. Do not switch your nutrients abruptly.
- Keep your grow space well ventilated. This will ensure even temperatures throughout and also help dissipate moisture.
- Adjust your lights. As your plants stretch, you may need to adjust your lights to keep them a suitable distance from your canopy and avoid burning your plants.
- Continue supporting your plants using stakes, trellises, or screens. It’s not uncommon for some cannabis plants to buckle under the weight of their flowers. By supporting them, you’ll not only prevent their branches from breaking, but you’ll also allow them to focus their energy on developing flowers rather than dealing with the physical stress of staying upright.
- Dial in your nutrients and water. Flowering cannabis plants typically take up fewer nutrients and water than vegging plants. Hence, it’s not uncommon for beginner growers to run into issues such as overwatering and nutrient burn during the bloom phase. Sticking to a feeding calendar, using organic nutrients, and growing in super soil can help prevent these issues. Also remember to meticulously check the pH of your water and nutrients to avoid running into pH issues during this critical time.
- Keep regular tabs on the ripeness of your flowers by checking their calyxes, trichomes, and pistils.
Prior to harvest:
- Remember to flush your plants with nothing but pH-regulated water for at least 1 week prior to harvest. If you’re growing your plants using organic nutrients, flushing is less important.
- Avoid high humidity at all costs. Mature cannabis flowers can easily trap moisture, and a single case of bud rot can significantly impact the quality and size of a harvest.
- Prepare for harvest. Clean your trimming equipment, setup up your drying racks, and prep your workspace to make the harvest process as easy as possible.
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Mistakes to avoid during the flowering phase
- Causing your plants any kind of stress. Whether it’s a nutrient deficiency, overwatering, or healing a broken branch – any stress your plants endure during their bloom phase will take their energy away from developing flowers. Avoid this at all costs to ensure your plants produce the biggest, most resinous flowers possible.
- Pumping your plants full of bloom nutrients. This is a common mistake among rookie growers who fall into the trap of thinking that more nutrients will produce bigger buds. Like with many things in life, less is more in the world of cannabis cultivation. If you’re new to growing, follow a feeding calendar and learn to read the needs of your plants so you can feed them only when they need it.
- Sudden changes in light and nutrients. Take the time to give your plants a gradual transition from veg to bloom to avoid stressing them – you’ll be glad you did come harvest time!
- Growing in unfavourable conditions. Excessive heat and humidity are your biggest enemies during the bloom phase, as these conditions can attract pests and pathogens that’ll stunt the development of your flowers or even render them completely useless.
- Harvesting too late or early. Knowing when to harvest your buds is key!
The cannabis flowering phase is one of the most eagerly awaited moments on a grower’s calendar. And it’s no wonder why – seeing your plants grow heavy with thick, fragrant flowers is a true sight for sore eyes.
Now, by understanding the unique needs of your budding plants, you can ensure that their transition into bloom and the coming weeks in flower run as smoothly as possible. Trust us, it’s worth it – in a few weeks, you’ll be rewarded with delicious and potent buds that make for a delectable experience!
Do you have your own tips for mastering the cannabis flowering phase? Share them with us and our readers using the comments below. Happy growing!
- Disclaimer:Laws and regulations regarding cannabis cultivation differ from country to country. Sensi Seeds therefore strongly advises you to check your local laws and regulations. Do not act in conflict with the law.
