Why are my tomato leaves turning purple?

Purple tomato leaves usually indicate phosphorus deficiency — most common when soil is too cold (below 15°C) or pH is outside 6.0–6.8, blocking nutrient uptake. Apply a phosphorus-rich fertiliser (12:61:0) diluted in water. Cold November–January nights in North India frequently trigger this symptom even in healthy plants. The colour self-corrects as temperatures rise. If purpling is on upper leaves only, check for thrips.