Feeding Your Cannabis Plants During the Flowering Stage

By Kent Gruetzmacher
Published: June 15, 2021 | Last updated: July 21, 2022 05:50:46
Key Takeaways

As a photoperiod plant, indoor cannabis growers must be aware of what their plants need at specific times during the lifecycle. Kent Gruetzmacher provides insight on what your plants crave during the bloom phase.

Source: Kyle LeGrow / LeGrow Creative

Whether you are a hobbyist grower or a commercial producer, the process of choosing the right fertilizers for the flowering stage can be quite daunting. To help alleviate some anxiety with the selection process, we put together the following criteria to consider for feeding cannabis plants during flowering.


Cannabis Growth Phases & Nutrient Requirements

When you look at various growth phases of the cannabis plant, you will see different periods demand specific fertilizers. These nutrient requirements are intimately tied to essential processes that occur throughout a cannabis plant’s life, from propagation to harvest.

Cannabis is a photoperiodic plant species. This means changes in daylight hours stimulate different growth phases in the plant. To illustrate, cannabis plants remain in vegetative growth when they have considerably longer days than nights (summertime). Conversely, the flowering phase begins when cannabis plants receive 12 hours of uninterrupted darkness each day. This light schedule resembles the conditions of autumn in nature. (Read also: From Seed to Harvest: The Life Cycle of Cannabis)

When light periods change, cannabis is genetically wired to respond with specific growth phases. For cannabis plants to thrive in each of these growth periods, they require very specific nutrients. As such, hydroponic product companies have developed complex fertilizers to meet the nutrient demands of cannabis during every stage of growth.

N-P-K Ratios During Veg & Flowering Stage

cannabis plant in the beginning of the flowering stage


Anyone who has read the label of a nutrient bottle has doubtlessly seen the “N-P-K” ratio. This ratio represents the amount of nitrogen (N), phosphorus (P), and potassium (K) found in different fertilizer products. When it comes to feeding cannabis plants, the N-P-K ratio of appropriate macronutrients will change with the different growth phases.

During vegetative growth, cannabis plants demand high amounts of nitrogen. By keeping up with nitrogen demands during this phase, you will ensure the cannabis plants stay green and hardy. This nitrogen must also be slightly counterbalanced with phosphorus and potassium. (Read also: Starting Off Right: Feeding Cannabis in the Vegetative Stage)

Example N-P-K Ratio for Vegetative Growth: 24-14-11

As cannabis plants shift their nutrient demands during the flowering phase, they require less nitrogen and more phosphorus and potassium. If you look at any flowering nutrients for cannabis, you will see this shift represented in the N-P-K ratio on the bottle.

Example N-P-K Ratio for Flowering Stage: 2-8-4

To help alleviate any potential confusion around the N-P-K ratio, nutrient companies have developed feeding calendars to accompany their products. These calendars easily direct you on when to change nutrient regimes throughout a cannabis plant’s lifecycle. Importantly, calendars give you the ability to witness the N-P-K ratio changing from vegetative growth to flowering on specific dates. (Read also: 5 Flowering Stage Tips for Cannabis)


Bloom Booster

Nutrient companies have also created bloom boosters that are designed to further stimulate flower growth. These bloom boosters feature inflated N-P-K ratios for flowering that utilize much higher amounts of phosphorus and potassium.

Example N-P-K Ratio for Bloom Boosters: 0-50-30

Bloom boosters present a somewhat divided subject among cannabis growers. Many feel cannabis plants can only handle certain amounts of phosphorus and potassium — anything beyond that threshold is considered extraneous. Some growers swear by bloom boosters, stating they are necessary for a big harvest, while others take a more passive approach during flowering. (Read also: Critical Perspectives on Bloom Boosters for Flowering)


In the modern cannabis industry, growers have more options than ever when it comes to feeding their plants. While it’s great to see such growth in the industry, choosing the right products can be quite daunting. All things considered, for both flowering and vegetative growth, it takes a discerning eye to understand what’s best for your plants.

It’s always a good idea to let your skill set and knowledge base dictate your approach to fertilization. If you are a novice grower, it is recommended you follow the directions on the feeding calendar. Conversely, experienced horticulturists have the confidence to critically assess nutrients and develop their own fertilization regimes. Either way, cannabis plants will always demand different variations of the N-P-K ratio, and we will continue to match our products against these requirements from mother nature.


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Written by Kent Gruetzmacher | Writer, Owner of KCG Content

Profile Picture of Kent Gruetzmacher

Kent Gruetzmacher MFA is a Colorado-based writer and owner of the writing and marketing firm KCG Content. Kent has been working in the cannabis and hydroponics space for over a decade. Beginning in California in 2009, he has held positions in cultivation, operations, marketing, and business development. Looking specifically to writing, Kent has worked with many of the leading publications and marketing agencies in the cannabis space. His writing has been recognized by such icons as Steve D’Angelo and Rick Simpson.

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