Lemon balm is a perennial herb in the mint family, grown for its lemon-scented leaves used in teas, cooking, and as a mild calming herb. It forms a bushy clump 18–24 inches tall and attracts bees and other pollinators when allowed to flower. In Zone 6b it dies back in winter and returns reliably from the roots each spring.
Like other mints, lemon balm spreads and self-seeds aggressively. Cut plants back before they flower to limit seeding and to encourage fresh leaf growth. It tolerates partial shade and poor soil, but the best leaf flavor comes from regular harvesting and a hard midseason cut.
Powdery mildew
White or grey powdery coating on leaves — usually starting on older growth in humid conditions or when nights cool.
Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.
Mint Rust
Small orange or rust-colored pustules on the undersides of leaves, followed by yellowing, distortion, and leaf drop. Stems may show swelling.
Remove and destroy infected foliage. Avoid overhead watering and improve air circulation. Cut plants to the ground and dispose of debris in severe cases. Do not compost infected material.
Septoria Leaf Spot
Small tan to brown spots with dark borders on leaves, often with tiny black specks at the center. Spots merge and lower leaves yellow and die.
Remove infected leaves and avoid overhead watering. Space plants for airflow and rotate planting location each year. Apply a copper-based fungicide if spread continues.