Flowering stage in Cannabis plants: a guide for beginners

In this article, you’ll find information about the Cannabis flowering, week by week, with photos and pictures. The flowering stage in Cannabis plants is the period when they grow their buds. After some weeks of vegetative growth, Cannabis plants will be able to flower when the photoperiod switches. Learn how to take care of your plant in this stage to harvest quality buds!

When does the Flowering stage begin?

Flowering stage outdoors

Growing outdoors, plants will start the flowering stage when the days grow shorter, usually when Autumn is coming.

Flowering stage indoors

For Cannabis plants to enter the flowering stage in indoor crops, the photoperiod must be switched to 12 hours of light / 12 hours of darkness schedule.

Autoflowering strains don’t need a photoperiod change to start flowering, their vegetative stage lasts around 4 weeks and then it switches stages automatically.

How long does the flowering stage take?

The duration of the flowering stage varies among different strains.

The flowering stage in Cannabis plants usually goes from 8 to 11 weeks, depending on the strain. It’s usually divided into weeks or three stages. The flowering period for Indica strains is typically around 8 weeks, but it may take up to 10 weeks. Sativa strains may take up to 10-12 weeks. Typically, hybrid strains will take up to 6-10 weeks to fully develop.

How do I know if my plant is male or female?

Here’s a quick visual guide on how to tell if your Cannabis plant is male, female or hermaphrodite. For more information and tips on how to find out, read our full article on determining the sex of a Cannabis plant.

Full article: Determining the sex of your Cannabis plants

Basic growing requirements for flowering Cannabis plants

Lighting

Light is very important in every stage in the Cannabis plant life cycle, but in the Flowering stage is key maintaining a Photoperiod: 12 hours of light / 12 hours of darkness. Do not interrupt the dark periods by opening “just for a sec” your growing environment. Light contamination may cause your plant to slow the budding process or even to revegetate (go back to veg stage) or start producing hermaphrodite flowers.

Temperature

Cannabis plants in the flowering stage thrive in temperatures around 18° – 26°C. Consequently, temperatures below this range may affect negatively the plant, or even kill it if it’s exposed to freezing temperatures for a long period. Temperatures under 17°C may slow the plant’s growth and very low temperatures (under 2°C?) may damage the plant irreversibly. On the other hand, high temperatures also affect the plant negatively. Temperatures over 28° C may cause problems such as stunted growth, burnt leaves, too heavy evaporation of water, excessive dryness, etc.

Humidity

As well as keeping temperatures within those “warm” ranges, taking care of the relative humidity in the growing environment is key. Relative humidity measures how much humidity is present in the air expressed as a percentage.
Humidity must be kept ideally between 40-50% in this stage. Higher levels of humidity may cause problems such as mold and fungi.

Nutrients for Cannabis plants in the flowering stage

The main nutrients that the Cannabis plant needs to develop are Nitrogen (N), Phosphorus (P) and Potassium (K). 

When the plant starts to bloom, the concentrations of P and K must be increased progressively, while the N concentrations are lowered. That is why there are specific fertilizers for vegetative growth and flowering. 

Other secondary nutrients will be necessary for the correct development of the plant. These are Magnesium (Mg), Calcium (Ca) and Sulfur (S). Finally, the micronutrients are necessary but in a minimum concentration. These are Zinc (Zn), Manganese (Mn), Iron, (Fe), Boron (B), Chlorine (Cl), Cobalt (Co), Copper (Cu), Molybdenum (Mb) and Silicon (Si). 

So which is the best feeding plan or nutrient application schedule for my plant? That’s up to each grower, but bear in mind you’ll need to add these nutrients, via foliar, liquid or solid fertilizers. Even when growing organic, usually having your plant in plain soil is just not enough for the plant to produce big fat buds.

Several brands of fertilizers offer fertilizer kits specially formulated for each stage with the necessary nutrients. Start with the dose indicated by the manufacturer or even 1/2 lower to avoid saturation and gradually increase the amounts until the desired results are achieved.

Watering

Water your plant regularly with clean, safe and water. Certainly, using chlorine-free or filtered water leads to better results. Always avoid overwatering and watch for good drainage. How to know when to water a Cannabis plant? A good test might be to stick a finger down a few cms or an inch into the soil and if it’s dry, then you’ll know it is time to water.

Ventilation

Ventilation and airflow are key for Cannabis plants to thrive and grow healthy. In this stage, they need air not only to breathe and grow their bodies but also good ventilation to avoid the formation of mold, fungi, and rot. A good fan moving the air inside your growing environment helps a lot, but beware not to point it directly to the buds. An exhaust fan is great for increased ventilation and air movement, this also helps lowering humidity. If the exhaust fan is not enough, a dehumidifier is definitely the best and easiest solution for keeping humidity at range.

pH levels

pH levels must remain between 6.5 and 7 when growing in soil. Most nutrients are available for the plant in the growing medium only between this range of pH. pH levels out of this range may cause your plant to experience nutrients deficiencies and toxicities because the nutrients may be in the soil but the plant cannot absorb them.

Container size

The size of your container is always related to the plant’s size. Are you growing in your garden soil? In pots with soil? In buckets? Hydro? The bigger the container is, the more chances of getting a bigger plant you have. Remember to transplant your tree before the flowering stage begins to avoid stressing the plant or accidentally damaging it.

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Flowering stage in Cannabis plants week by week

Flowering initiation stage – week 1-3

From week 1-3 plants stretch and grow in size and height. This phase is also known as the transition phase, as plants experiment drastic changes these days. Plants stretch and may double their size in this phase. The female Cannabis plant starts blooming by producing pre-flowers, their pistils look like “white hairs”.

Towards the end of the third week, the plant starts forming its bud sites in the plant nodes (where the main stem and the branches meet). Look for clusters of female preflowers.

All those places where white pistils have been growing are future bud sites. If you accidentally cut the preflowers along with the fan leaves, there’s a chance that that bud stops growing. You may lightly defoliate your plant during this phase, but be careful not to touch or damage the forming bud sites.

Look at the color of the fan leaves and the general look of each plant to have a better idea of their health and needs. The fan leaves should be vibrant green, not too light nor dark. For example, yellow and discolored leaves may indicate a deficiency, while dark and clawing leaves may indicate nutrient burn. Track these changes as soon as you notice them for a better chance of diagnosing your plants correctly and in time to heal them!

It’s also important to check for pests, mold, and fungi before our plants start making their buds. Most importantly, to eliminate these at this point is usually easier than doing it later into the flowering stage.

Mid-Flowering stage –  week 4-5

From week 4-5 plants stop growing in size and start growing, fattening their buds and darkening their pistils.

  • Humidity levels need to be lowered to 40-50%
  • It’s best to slightly lower temperatures in flowering
  • Temperatures with lights on 18-26 ° C (avoid high temperatures)

At this stage, you should continue to train your plant if you started some weeks earlier and you should be seeing some changes. In addition, if you need to tie or move your plants, bear in mind that now they are putting all their efforts into growing buds, so any stress or damage may slow that process. 

Remember to continue to move your lamp or plants so they maintain their adequate distance. Now your plants are growing at a fast rate and they need their feeding and watering schedule to be followed for optimal results.

It’s normal at this phase to see some old leaves yellowing and finally turning brown and falling. That’s because some nutrients are “mobile”, meaning that once the plant has absorbed them, they can be stored and distributed inside the plant as needed. So an old leave may “send” nutrients to the newer ones and once the plant doesn’t need that leave anymore, it lets it die and fall. If you notice lots of leaves yellowing or any changes in color or texture in the new or old leaves, check for nutrient deficiencies or burn!

Late flowering / Ripening stage – week 6 to harvest

In the last few weeks, buds gain the most weight. They are sticky to the touch and can be very smelly. You are very close to reaching your goal = harvesting!

  • Bring down humidity levels: 35-45% if possible
  • Increase the temperature difference (day/night)
  • Temperatures with lights on 18-24 °C 
  • Start checking trichomes for signals or ripening to know when to harvest 
  • Remember to flush your plants 1-2 weeks before harvest

Most importantly, buds are now covered in trichomes, which are rich glandules for secreting THC and other cannabinoids. These are responsible for the stickiness in the colas. Depending on the strain and the breeding, these buds may have strong aromas, reminding of fruits, flowers, and spices for example. 

In this stage of the Cannabis plant, pistils may show white, cream and brown colors. They also start curling inwards and they get covered in trichomes. Similarly, trichomes also change colors and you should pay close attention to these changes because they are one of the best clues for knowing when is the best time for harvesting.

Remember you’ll need to do flushing prior to harvesting, so calculate your times in advance! 

Flushing your plants (week 8-10)

Flushing a Cannabis plant is basically to run a lot of water through its growing medium (soil, for example) to get rid of the excess of salt and mineral nutrients. This action forces your plant to use up any amount of nutrients previously absorbed. The result will be buds with better flavor and aroma. The excess of fertilizer in your Cannabis plant may result in buds which are harsh to the throat when smoked and

Flushing with clean, room temperature water will help to get rid of fertilizer excess in the soil.

Two weeks before harvesting is usually a good moment to start flushing your plants and watering with water only and no fertilizers until the harvesting moment.

Regarding the amount of water needed, a good rule is to calculate 3 times the volume of the pot. For example, if your pot is 5 liters, you can flush with 15 liters of water per pot. An easy way of doing this is carefully placing each plant in a shower or bathtub and add the water gradually to the soil, without drowning the plant. The excess of water will slowly drain from the bottom of the pot.

A good visual sign is that, in the beginning, the water coming from the bottom of the pot will be dark and will gradually turn to a lighter color. If you don’t have a bathtub, you can do it inside the tent. Place a container under the pot for collecting the excess water, be careful or this may result in a bit of a mess. By running this process once in each plant, most of the salt buildup should flush away from the substrate.

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