Lettuce Leaf Basil

Basil commonly suffers from downy mildew (often first seen as yellow spots on top leaves with a fuzzy growth underneath), especially in humid, crowded conditions. Remove badly infected leaves, improve airflow (space plants and thin if needed), and water at the soil line in the morning so foliage stays dry; if it keeps spreading, use a labeled downy-mildew fungicide appropriate for edible herbs. Aphids are also frequent—spray them off with a strong jet of water and repeat every few days until the colonies stop returning.

Start harvesting leaf basil at about 50 days when plants are well established with plenty of healthy leaves and can support regular pinching. Pick leaves in the morning, and harvest by removing leaf pairs just above a node (pinch the tops) to encourage bushy regrowth. If leaves become bitter or the plant starts forming flower buds, harvest immediately and expect the flavor to shift sooner.