How to Fertilize Cannabis Plants During Flowering

In today’s sophisticated society, cannabis growers have more options than ever concerning cultivation products and methods. Due to widespread legalization efforts, the last two decades have seen amazing advancements in cannabis horticulture. These developments have been impactful on cultivation technology and methodology, as well as fertilization techniques. With a good deal of science behind them, growers today know exactly how to fertilize cannabis plants during flowering.

A trip to the hydroponics store quickly illuminates the fact that there are endless choices for cannabis plant food. The stores are adorned with extravagant display cases featuring nutrient products, feeding schedules, and success stories. A closer look reveals that many of these nutrients are created specifically for the all-important flowering phase.

Whether you are a hobbyist grower or a commercial producer, the process of choosing the right fertilizers for flowering cannabis 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.

Growth Phases & Nutrient Requirements

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

Cannabis is a “photoperiodic” plant species. This means, that changes in daylight hours stimulate different growth phases in cannabis crops. To illustrate, cannabis plants remain in vegetative growth when they have considerably longer days than nights. Because long days (18 hours of light) closely mimic summertime conditions in the natural world. Conversely, the flowering phase is initiated when cannabis plants receive 12 hours of uninterrupted darkness each day. This light schedule resembles the conditions of autumn time in nature.

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, hydroponics product companies have developed complex fertilizers to meet the nutrient demands of cannabis during every stage of growth.

N-P-K Ratio

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.fertilize cannabis plants during flowering

During vegetative growth, cannabis plants demand high amounts of nitrogen (N). By keeping up with nitrogen demands during this phase, you will ensure that the cannabis plants stay green and hardy. This nitrogen must also be slightly counterbalanced with phosphorus (P) and potassium (K).

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 (N) and more phosphorus (P) and potassium (K). 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 Phase: 2-8-4

To help alleviate any potential confusion around the N-P-K ratio, hydroponic 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. As such, they tell you exactly how to fertilize cannabis plants during flowering.

Bloom Boosters

Nutrient companies have also created “bloom boosters” that are designed to further stimulate flower growth in cannabis plants. These bloom boosters feature inflated N-P-K ratios for flowering that utilize exorbitant amounts of phosphorus (P) and potassium (K).

Example N-P-K Ratio for Bloom Boosters: 0-50-30fertilize cannabis plants during flowering

Bloom boosters present a somewhat contentious subject among cannabis growers. Many feel that cannabis plants can only handle certain amounts of phosphorus (P) and potassium (K) – anything beyond that threshold is considered extraneous. It’s tough to say whether bloom boosters are 100% necessary for a good harvest, although certain growers swear by them.


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 hydroponics vertical, 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. To this end, if you are a novice grower, it is recommended that you follow the directions on the feeding calendar. Conversely, experienced horticulturists have the confidence to critically assess nutrients and develop their own methods to fertilize cannabis plants during flowering. 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.


This article was originally published in the June 2021 issue of Maximum Yield Cannabis Magazine.