Nutrient requirements across the cannabis life cycle

Cannabis's nutrient demand is not constant but follows the physiological shift from vegetative growth to generative bud formation. Each phase requires a different ratio of nitrogen (N), phosphorus (P) and potassium (K).

A nutrient program left unchanged across the entire cycle ignores this shift and is a common cause of nitrogen toxicity in late flowering and of potassium or phosphorus deficiency during active bud formation.

Nitrogen is a building block of chlorophyll, amino acids and structural proteins — demand correlates directly with the increase in leaf mass and is therefore highest during the vegetative stage.

Phosphorus, as a component of ATP and nucleic acids, drives cell division and energy transfer; potassium regulates stomatal opening, osmotic pressure and sugar transport into bud tissue. Both processes dominate from the onset of flowering, which shifts the ratio in favor of P and K.

Seedling (day 0–14): EC 0.4–0.8 mS/cm — seed reserves largely cover initial demand, overfertilization is the bigger risk here than deficiency.

Vegetative (until the light switch): NPK ≈ 3:1:2, EC 1.0–1.6 mS/cm — nitrogen-heavy for leaf mass growth.

Stretch and early flowering (first 1–3 weeks after the switch): transition phase — gradually lower N, gradually raise P and K.

Mid-flowering (main bud formation): NPK ≈ 1:3:3, EC 1.4–2.0 mS/cm — peak K demand for sugar transport into the buds.

Late flowering/ripening (last 1–2 weeks): gradually lower EC toward 0.6–1.0 mS/cm, N down to near zero.

Soil: microbial nitrogen mineralization buffers fluctuations, error tolerance is high, but the response to nutrient adjustments is slower.

Coco coir: high cation exchange capacity binds Ca²⁺ and Mg²⁺ preferentially over K⁺ — routine Cal-Mag supplementation is practically mandatory, but the response to corrections is significantly faster than in soil.

Hydro: no buffering — the nutrient solution IS the root zone. EC and pH drift must be checked daily, replenishment happens via volume changes rather than the watering cycle.

Autoflowering lines have a fixed, short lifespan of around 10 weeks without a clearly separable veg/flowering switch set by the breeder. Nutrient transitions therefore need to be gentler, and EC ceilings should sit around 20–30 % below the values for photoperiod plants.

Overfertilized autoflowers cannot compensate for the stress through an extended vegetative recovery phase the way photoperiod plants can — the yield loss is permanent.

Keep a weekly log of EC/pH at both input and runoff, not just checking the input.

Change the NPK ratio on the calendar day of the phase switch, not reactively after symptoms appear.

Plan a flush with pH-corrected water before every major phase change to remove leftover salts from prior feeding.

Using the same nutrient program for photoperiod and autoflowering plants without adjusting the EC ceiling.

Keeping nitrogen high into late flowering — 'more green = more yield' is not true and costs bud quality as well as flavor.

Lowering EC abruptly instead of gradually during the flush, which acts like additional salt stress.

Strain differences in nutrient uptake speed are real — the target values given are ranges, not fixed values, and should be fine-tuned based on plant response.

In living-soil systems, the microbial community handles part of the phase-based transition itself; the EC phase model applies primarily to liquid feeding in coco coir, hydro, and classic potting soil.