pH值是在0到14的刻度上衡量溶液酸碱度的指标，7为中性。在水培和土壤种植中，pH值直接控制哪些营养素对植物根系具有化学可用性。大多数作物在水培系统中pH 5.5–6.5时生长最佳。
关键事实
- Scale runs 0–14: below 7 is acidic, above 7 is alkaline, 7 is neutral
- Hydroponic target range: 5.5–6.5 (slightly acidic) for most crops
- Soil target range: 6.0–7.0 depending on crop
- Out-of-range pH causes nutrient lockout — plants cannot absorb minerals even if present
- pH drifts over time as plants absorb nutrients and water evaporates
- Adjust with pH Up (potassium hydroxide) or pH Down (phosphoric acid)