Flowering for Yield and Quality

The final stage

Once a plant has completed enough vegetative growth and is of a desirable size for the grow space, your plants are ready to begin flowering.

Congrats on making it to this stage!

For most growers, a cannabis plant’s flowers are its only valuable part. Because the flowers are the reason for growing, special attention must be paid to the plant during this critical time.

The goal during flowering is for the plants to grow very large, dense, and resinous flower clusters (many times called “buds”).

This can be accomplished even by new growers that pay attention to the following:

  • Genetics
  • Stretching/shoot competition
  • Bud-site access to light and airflow
  • CO2 levels
  • Humidity
  • Nutrition

Flowering and photoperiods

Cannabis is an annual plant that has evolved to respond to daily day/night photoperiods. As days grow shorter and winter nears, the plant begins to mature (photoperiodism).
When cannabis receives 12 uninterrupted of darkness per day, it will begin to flower. This photo period must be maintained throughout flowering.

  • This is achieved with a timer-controlled light, and a lightproof grow space.
  • Any light during scheduled “dark period” greatly stresses the plant.
  • This may result in the plant reverting back to vegetative growth without producing buds.
  • It may also result in the expression of stress-related hermaphroditism and the pollination of a crop.

Flowering Timeline for Cannabis L. Sativa

  • Week 1-3 – Transition to flowering (elongation)
  • Week 3-4 – Budlets form (aroma)
  • Week 4-6 – Buds develop in size and density
  • Week 6-8 – Buds ripen, styles darken, – some strains may spend more time in this stage
  • Week 8+ – Flowering ends, final flush, harvest

This Fruity Pebbles plant is about 30 days into flowering

The Flowering Stretch

During the first two weeks of flower,
when the plants are exposed to their
longest period of darkness for the first
time, the shoots will elongate rapidly.Many strains of cannabis double in
height during flowering.Knowing this grants the grower some
control over the plant’s final size.As a general rule, you should begin
flowering when your plant is half the
final desired height.

During this time, it is the grower’s job to
control shoots that stretch too far beyond the others.Growers can can use plants ties to bend
and secure these outliers or a trellis to
tuck the canopy. Either or both will help
control the flowering stretch.

Canopy control: Outliers

  • Outliers: Shoots that grow tall and stretch beyond the others. These overly-dominant shoots will end up hogging the light, shading many other bud sites, and hindering their development.
  • Growers can employ plant ties to help control outliers. Start by very gently bending these outliers over and bringing them closer to the rest of the canopy.
  • Small adjustments should be made, especially to more “woody” shoots. When bending a shoot over, stop when you start to feel resistance. Ignoring resistance can result in broken shoots, which should be avoided during flowering.
  • Once the shoot is in an acceptable new position, secure it using a plant tie.
  • This should be done throughout flowering.

Canopy control: Underliers

  • Underliers: Lower axillary/lateral shoots that are not exposed to canopy-light will begin to stretch very rapidly during flowering. These shoots will be thin and spindly with comparatively few bud sites due to stretched internodes. The buds that do develop here are very small, poorly-developed, and sparse. These shoots consume nutrients and energy that could be used by more dominant bud sites.
  • Underlying shoots also become a major nuisance when they grow up close to, and in-between larger more dominant shoots. This over-crowded canopy scenario limits the light and airflow and contributes excess humidity, slowing transpiration and growth. To avoid an overall reduction in bud development and yield, most lower spindly branches should be removed, especially when they directly compete with a major shoot.
  • This should be done 1 – 2 times during flowering.

Internodal Spacing

  • Internodal spacing should be controlled throughout a grow, but special consideration should be given during flowering.
  • The amount, and spectrum of light received at the branch determines how much it stretches.
  • Phytochromes detect red and blue light intensities and ratios compared to FR & UV to determine how much to stretch.
  • Fan leaf shade reduces amount and ratio of lights.
  • Defoliation reduces internodal stretching.
  • Starting with a good commercial light helps tremendously.

Canopy control: Defoliation


This should be done 2 – 4 times during flowering.

Nutrition for Flowering Cannabis

  • In flowering, the cannabis plant can benefit from elevated nutrient levels. As the flowers mature, the plant can especially begin to utilize an increasing amount of Phosphorous.
  • This is due to the plant’s increased demand for phosphorous dependent energy including the formation and storage of sugars – which are particularly needed for processes during the long 12-hour nights when it isn’t receiving energy from light.
  • Many well-known nutrient schedules account for this by including a “Bloom” supplement that the grower increases in dose as the plant matures through flowering. This is also evident in the CCS nutrient schedule.
Week #: Veg 1 Veg 2 Veg 3 Veg 4 Flower 1 Flower 2 Flower 3 Flower 4 Flower 5 Flower 6 Flower 7 Flower 8
Stage Seedling Early Growth Late Growth Transition Early Bloom Early Bloom Mid Bloom Mid Bloom Mid Bloom Late Bloom Ripen Flush
Base Nutrient FloraMicro 0 2 3 3 4 4 4 4 4 4 2.5 0
Base Nutrient FloraGro 1 2 3 3 4 3 0 0 0 0 0 0
Base Nutrient FloraBloom 1 2 3 3 4 5 6 6 6 6 5 0
Resiliency Armor Si 0 0 0 1 1 1 2 2 2 2 0 0
Weight Liquid KoolBloom 0 0 0 0 0 0 2 2 3 3 0 0
Aroma Floralicious Plus 0 0 0 0 1 1 1 1 1 1 1 0
Flush FloraKleen 0 0 0 0 0 0 0 0 0 0 0 10
Vigor CaliMagic 1 2 2 2 3 3 3 3 3 3 3 0
Flavor FloraNectar 0 0 0 0 0 0 5 5 5 5 5 0
Ripening Dry KoolBloom 0 0 0 0 0 0 5 5 5 5 ¼ tsp 0
Root Health Hydroguard 2 2 2 2 3 3 3 3 3 3 3 0

This is the GH-based nutrient schedule written and used by Colorado Cannabis School.

Note: This was designed for use with Fox Farm soil, Hydroponics, or Coconut Husk, 750-1000w HPS, 700-900 ppms of CO2.
Nutrient levels may need to be adjusted for alternative applications, week 4 & 7 may need to be repeated for certain strains.

Special Attention to Humidity & Airflow

  • Humidity and Airflow become a special focus during flowering.
  • Large and dense buds can harbor a lot of excess moisture and limit airflow. This greatly limits transpiration and growth, and can lead to the development of mold, mildew and as a result: significant crop loss.
  • The first sign of an overly-humid environment is shriveling at the tips of the flower’s styles, and condensation on the grow space surfaces.
  • If this is evident, take action to remove the humidity right away. This includes increasing fresh air exchange, and/or the addition of a dehumidifier.
  • In closed-loop systems, dehumidifiers are required in flowering areas. Ideally, the humidity should be kept between 40-50% at around 80F.

Ripening

  • During the last couple weeks of flowering, the buds will reach their final size and trichome density.
  • When a plant is near ready, the styles will have turned mostly orange/brown.
  • When the plant is near ready, take a jeweler’s loupe and closely examine the trichomes. Look for them to become mostly cloudy with a few turned amber.
  • Once this occurs, the plant is ready to be harvested.

The Harvest

Trimming/Manicuring

  • Trimming your flower is important for achieving a
  • pleasant end product. The goal is to increase the
  • trichome to plant matter ratio.

Trimming

  • Soon after harvesting, remove the fan leaves, and less productive sugar leaves close to the bud. When removing, cut the stem as close to the stalk as possible.
  • Hang the plant upside down. This will allow the bud structure to tighten a little more as it dries.


Trim may be saved for used in cannabutter.


Drying

    • Drying is critical to removing a lot of the excess moisture from the harvest.
    • Preferred Drying Atmosphere:

Temperature: 70°F
Humidity: 45%

  • Your harvest should dry for about a week, or until the stems snap cleanly instead of bending.
  • You’re ready to begin curing your buds!

Curing

Preferred Curing Atmosphere:

  • Temperature: 70°F
  • Humidity: 60%

  • Curing is an important step to a top shelf product.
  • Jars must be burped regularly with fresh air for the first couple weeks of curing.
  • During curing, chlorophyll continues to degrade and off gas. This is the unpleasant “fresh cut grass“ smell/flavor of newly harvest buds.
  • Curing enhances the pleasant terpene profile of your flower.
  • Reduces “harshness,” which generally results in less coughing.