pH

pH is the most critical and most frequently mismanaged parameter in cannabis cultivation. The pH scale measures hydrogen ion concentration logarithmically, meaning each whole number represents a 10x change — pH 5 is 10x more acidic than pH 6 and 100x more acidic than pH 7. Cannabis evolved in soils with slightly acidic pH (6.0-6.8), and its root system can only absorb specific nutrients within narrow pH windows. When pH drifts outside the optimal range, individual nutrients become "locked out" — chemically present in the soil or solution but biologically unavailable to the plant. Specific lockout patterns: low pH (under 5.5) locks out calcium, magnesium, and phosphorus while making iron and manganese toxically available; high pH (over 6.8) locks out iron, manganese, boron, copper, and zinc while making calcium and magnesium less available. Optimal pH ranges by growing medium: Hydroponics/DWC — 5.5 to 6.0; Coco coir — 5.8 to 6.3; Peat-based soilless — 5.8 to 6.5; Living soil — 6.2 to 6.8 (the soil microbiome buffers pH naturally). pH must be tested at three points: source water before mixing nutrients, finished nutrient solution before feeding, and runoff drainage after feeding. Significant runoff vs feed-in pH drift indicates the growing medium is shifting and may need flushing. Adjustment is performed with phosphoric acid (pH down) or potassium hydroxide / silica (pH up). Growers should invest in a quality calibrated pH meter (Bluelab, Apera, or Hanna) and recalibrate weekly with pH 4.0 and pH 7.0 reference solutions.