Damping Off: Why Seedlings Rot at Soil Line

Seedlings brown at base = damping off from: contaminated soil, poor airflow, waterlogged soil.

Prevention: sterile soilless mix (perlite/vermiculite/peat). Sterilize trays (1 tsp bleach/gal water). Remove humidity dome at first sprout. Fan on low, 3 ft away, oscillating. Water sparingly—drainage holes mandatory.

Light: 14 hrs/day (grow lights or cool+warm fluorescent). 8 hrs dark. Lights 3" above plants. Fertilize at 2nd true leaf: half-strength seaweed/fish emulsion.