Basil is known as the easiest herb for beginners, but even small mistakes can ruin your harvest. In this episode of Window Sill Botany, we explain why your fragrant plant suddenly looks sick, how to tell the difference between mildew, bacteria, pests, and simple cold damage, and what immediate steps will save your plant. You will learn a clear treatment plan for black spots on basil leaves, from pruning and root checks to proper base watering and airflow, plus simple prevention rules to keep your harvest fresh and edible.