What changes in your feeding when the plant flips to flower?
The photoperiod shift triggers an internal resource redistribution: nitrogen used to build vegetative tissue is dialed back, while potassium — which regulates stomatal opening, sugar transport, and turgor in reproductive tissue — goes up. This transition isn't abrupt; it happens over the first two to three weeks of bloom during the stretch.
Bevan et al. (2021) measured cannabis nutrient demand across growth stages under controlled conditions and found that optimal N during flowering sits at 100–150 ppm, lower than typical veg-stage values. Cutting N at the right time isn't neglect — it's what the plant is actually asking for.
What are the verified N, P, and K ranges for full bloom?
The most-cited peer-reviewed studies on cannabis nutrition converge on similar ranges for mid-to-late flower:
- N (nitrogen): 100–150 ppm (Bevan et al. 2021).
- P (phosphorus): 30–60 ppm. Westmoreland & Bugbee (2022) found that above this range there was no improvement in floral biomass and clear antagonism with micronutrients.
- K (potassium): 150–250 ppm. Saloner & Bernstein (2023) identified K as the macro with the highest relative demand during the flowering stage.
These aren't numbers from a single trial or a manufacturer's feeding chart — they come from replicated, controlled-environment studies with cannabis measured at each growth stage.
Why doesn't excess phosphorus build bigger buds?
The "PK booster" myth originated in the early days of hydroponic cannabis, when growers — working without crop-specific data — borrowed feeding charts from tomatoes and peppers, which have higher P demands than cannabis. The result is that many products on the market push P well above what the plant actually needs.
The problem isn't just wasted nutrient: excess phosphorus directly competes with iron and zinc uptake in the root zone. Westmoreland & Bugbee (2022) documented that above 60 ppm P, availability of Fe and Zn begins to decline — both micronutrients are critical for chlorophyll synthesis and bloom-stage enzymes. The practical outcome: buds with interveinal chlorosis, not bigger buds.
What about potassium — does more K actually help?
Potassium genuinely is the macro that rises in flower, but it also has a ceiling. Saloner & Bernstein (2023) found that peak K demand occurs in mid-to-late bloom and optimal values sit at 150–250 ppm. Above that, antagonism with calcium and magnesium kicks in: excess K blocks Ca²⁺ and Mg²⁺ absorption through competition at root ion channels.
The key is that K rises relative to N, not in disproportionate absolute terms. The K:N ratio in full bloom typically runs 1.5:1 to 2:1 (more K than N), but never with K through the roof while Ca/Mg collapse.
How do you apply this in practice if you're not measuring in ppm?
Most home growers don't have photometers or solution analysis kits. The practical way to hit these ranges is to use a fertilizer formulated within the correct windows and follow the manufacturer's dosage — the nutrient curve is already built in — rather than stacking boosters on top.
- In flower, reduce the high-N component and increase the bloom formula (high K, moderate P).
- Don't stack multiple PK boosters: each one you add pushes P or K above the range without the rest of the solution knowing.
- Keep feeding pH in range (5.8–6.2 in hydro; 6.0–6.5 in soil/coco): outside that window P will precipitate even at the correct dose.
- Use the dose calculator at /calculadoras/dosis to dial in mL per part based on your system volume — don't eyeball it.
How does the feeding curve shift from week 1 to week 8 of flower?
Flowering isn't a single uniform block. It's typically broken into three phases: early flower (weeks 1–3, stretch + first pistils), mid flower (weeks 4–6, bud fattening), and late flower (weeks 7+, ripening and resin accumulation). Nutrient demand shifts across those phases:
- Early flower: N still moderate (~150 ppm), P and K rising gradually.
- Mid flower: N low (~100 ppm), K at its peak (200–250 ppm), P in range (40–60 ppm).
- Late flower: some growers run a flush or drop all macros; the evidence on whether this improves final flavor is debated and depends more on substrate and cure than on nutrition in the final days.
