Nutrients for the flowering of cannabis: beyond NPK

The transition from the vegetative to the flowering phase represents one of the most critical moments in the life cycle of cannabis, as plants undergo a deep metamorphosis that requires the adaptation of nutrients to the flowering stage in a precise and calculated way. The success of your grow largely depends on how you manage this transition, providing your plants with exactly what they need, when they need it. This includes both traditional macronutrients and those often forgotten elements that can make all the difference between a mediocre harvest and an extraordinary one.

When a cannabis plant faces the transition from the vegetative to the flowering phase, its metabolic priorities change radically. During the vegetative stage, the undisputed protagonist is nitrogen (N), which is responsible for leaf development and structural expansion, as well as being an essential nutrient for chlorophyll synthesis and green tissue development.

However, when plants enter the flowering phase, their demand for nitrogen decreases significantly, whereas their need for phosphorus (P) and potassium (K) increases. Phosphorus plays a key role in flower formation and energy transfer within the plant, which is vital for the development of dense and resinous buds. For its part, potassium regulates water balance, activates enzymes, and contributes to the synthesis of proteins and carbohydrates, which are all essential processes during flowering.

Changes in the nutrient requirements of the flowering phase

To adapt to the change in the cycle, growers must switch to fertilisers specifically formulated for the flowering stage. While a fertiliser with a 3-1-2 NPK ratio could be used in the vegetative stage (for example, 9-5-8), a 1-3-4 ratio is preferable for the flowering (for example, 5-9-9, or the classic PK 13-14).

This change should be made gradually to avoid stressing the plants. Instead of suddenly switching from a vegetative to a flowering fertiliser, making a gradual transition that allows the plants to adapt to the new nutritional ratios is always more effective. For instance, growth and flowering fertilisers can be mixed during the last two weeks of the vegetative cycle, so that nitrogen is progressively reduced whilst phosphorus and potassium are gradually increased.

During the first two weeks after the cycle change, most growers use nutrients for the flowering with a 5-7-10 NPK ratio. This trend becomes more pronounced as the flowering progresses, reaching ratios of approximately 6-10-15 in the middle stage, and always maintaining potassium as the predominant element.

In the final stages, it’s advisable to gradually reduce the nutrient intensity, returning to softer ratios such as 4-7-10 so the plants are prepared for the final flushing of the roots before harvesting. This progressive reduction prevents excessive accumulation of nutrients in the plant tissues, improving the taste and final quality of the product.

Skunk+ x Auto Skunk+

Pure Skunk Go Fast: rapid growth and high yield

Pure Skunk Go Fast is known for its rapid growth and high yield. It boasts a short 6-week flowering period indoors and a September harvest outdoors, making it ideal for maximizing yearly harvests. This strain offers a sweet and earthy aroma, over 18% THC, and delivers a calming effect, suitable for both beginners and experienced growers seeking efficiency and robust yields.

Secondary macronutrients: the great forgotten

While NPK is the basis of any nutrient plan, focusing exclusively on these three elements would be a huge mistake. Secondary macronutrients, particularly calcium and magnesium, perform equally critical functions during the flowering that should not be underestimated.

Calcium functions as a true cellular architect, as it’s fundamental for the development of robust cell walls that provide the structural support required during the flowering. In this phase, when buds gain weight quickly, calcium also strengthens the plants’ defences against pathogens. Moreover, it facilitates the absorption of other essential nutrients for the flowering and activates key enzymes involved in various metabolic processes.

Furthermore, magnesium (i.e., the central component of the chlorophyll molecule) is essential for maintaining efficient photosynthesis. During the flowering, when plants need to generate large amounts of energy for bud development, magnesium also contributes significantly to cell division and regulates the energy balance of the plant. This helps facilitate the formation of bridges between enzymes and ATP (adenosine triphosphate), which is the main energy carrier molecule in cells.

The deficiency of these secondary macronutrients can manifest itself in various ways and is often confused with other problems. A calcium deficiency is usually evident in new leaves with deformed edges or curled tips, while the lack of magnesium usually appears as interveinal yellowing that begins on older leaves and progresses to younger ones.

To prevent these deficiencies, many growers resort to specific Cal-Mag supplements, which are particularly important in hydroponic systems or when using reverse osmosis water or water that’s too soft, as these are naturally poor in these minerals.

Micronutrients: small quantities, big results

Micronutrients represent the third level of plant nutrition. Although they are required in much smaller quantities than those mentioned above, they perform equally vital functions.

Iron (Fe) is actively involved in the synthesis of chlorophyll and acts as an essential component of numerous enzymes involved in cellular respiration. Iron deficiency is typically manifested as an interveinal yellowing in young leaves, unlike magnesium deficiency, which first affects mature leaves.

Zinc (Zn) is essential for the synthesis of auxins, which are hormones that regulate flower development. A deficiency of this element can result in short internodes, small leaves, and malformed flowers, seriously compromising the yielding capacity of the plant.

Manganese (Mn) acts as a catalyst in photosynthetic processes and is actively involved in the formation of oxygen from water. Its absence can manifest as chlorotic mottling on the leaves while the veins remain green, which reduces the energy efficiency of the plant just when it needs it the most.

Boron (B), an element that’s often undervalued, facilitates the transport of sugars within the plant ― a crucial process that occurs during the flowering, when carbohydrates need to be transported towards the developing buds. Boron deficiency can cause stunted growth and malformed buds.

Although required in even smaller quantities, copper (Cu), molybdenum (Mo), and chlorine (Cl) participate in fundamental metabolic processes that intensify during the flowering. And silicon (Si), although technically not considered essential, provides structural resistance to plant cells and increases stress tolerance ― two qualities that are particularly valuable during the formation of heavy buds.

Determining the appropriate dosage of these micronutrients requires precision and observation, as needs may vary depending on substrate, type of strain, and growing conditions. It is best to follow the directions of the fertiliser manufacturer, as commercial products are usually formulated to meet the general needs of the plant and avoid any toxicity.

((Platinum Cookies x GDP) x Blue Power) x Gelatti

Apple & Bananas

Descended from a noble lineage, Apple & Bananas stems from a fusion of giants: First, Platinum Cookies was crossed with Grandaddy Purple and then intertwined with Blue Power; with this triad culminating in a warm embrace with Gelatti. Like stars in a cannabis sky, each ancestor brings a spark of genius, forging a legacy of balance and strength that can meet the needs of many users, especially of those seeking potency, thanks to her THC levels of up to 27%.

Common mistakes that compromise flowering

Despite the wealth of information available, certain nutritional errors remain extremely common among growers of all experience levels.

Overfertilisation is likely the most frequent mistake, especially among beginners. There’s a misguided belief that more nutrients for flowering will always yield better results, when in reality, excess can cause root and leaf “burn,” severely impacting plant health and final harvest quality. To avoid this, start with conservative doses and increase gradually only if necessary.

Nutritional imbalance is another typical issue. Providing the right quantities isn’t enough—the ratio between elements is equally critical. During flowering, alongside the NPK adjustments mentioned earlier, maintaining balance with secondary macronutrients and micronutrients is essential. An excess of certain elements can trigger antagonisms, hindering the absorption of others just as vital.

Neglecting pH levels in the growing medium and irrigation water is another fundamental error that locks out nutrients for flowering availability. pH directly determines which flowering nutrients roots can absorb. During this phase, maintaining a pH of 6.0–6.5 for soil and 5.5–6.0 for hydroponics is crucial to ensure optimal uptake, especially for pH-sensitive micronutrients like iron and zinc.

Nutrients for flowering adaptation based on genetics

Another often-overlooked factor is that different cannabis strains have distinct nutritional needs. Indica-dominant varieties generally respond better to higher phosphorus and potassium concentrations compared to sativas, which typically prefer more balanced formulations.

Long-flowering strains like tropical sativas also require sustained micronutrient levels that might be excessive for other genetics. Magnesium, for instance, often depletes in prolonged flowering cycles, manifesting as progressive yellowing that many growers mistakenly interpret as natural maturation.

Autoflowering strains, due to their rapid life cycle, need gentler formulations at all stages and are particularly sensitive to overfertilisation during the transition to flowering. For these plants, maintain moderate, stable concentrations and avoid drastic nutrient changes that could stunt their accelerated growth.

The art of personalised nutrition

The use of nutrients for flowering throughout this crucial phase goes beyond the simple adjustment of standard NPK ratios. This is a dynamic and highly customised process that must consider multiple variables, including genetics, the growing medium, water quality, and environmental conditions.

An experienced grower knows that the true mastery of fertilisation doesn’t consist of applying universal formulas, but of developing the ability to “listen” to each plant and providing it with exactly what it needs at each specific point of its development. This individualised approach, combined with solid technical knowledge, enables us to maximise the genetic potential of our strains, obtaining exceptional harvests in terms of both quantity and quality.

In short, the key to success lies in meticulous observation, flexible adaptation of nutritional regimes, and a deep respect for complex biological processes that transform simple mineral elements into lush flowers full of aromas, flavours, and potency.