My Basil Has Black Leaves Under Lights

Nutrient Deficiency

• When brown and/or black spots appear on mature basil leaves, it is a signal of potassium deficiency in the soil. Areas of the leaves may also turn yellow when potassium deficiency occurs. Treat the soil with potassium-rich fertilizer to replenish these nutrients and keep the basil plant healthy.

Bacterial Leaf Spot

• Bacterial leaf spot creates black and brown streaks on stems and spots on the leaves of basil plants. Bacterial leaf spot is a fungal growth that thrives in water. Moist leaves and standing puddles foster the growth of the fungus that creates leaf spot. Space basil plants far enough apart to allow air circulation between plants and around leaves of the plant. Ventilation will keep the foliage of the plant dry and prevent bacterial growth.

Watering

• Improper watering practices may lead to brown or blackened leaves on basil plants. Water droplets standing on leaves may burn in the sun. The light shines onto the water, magnifying the light. The hot water and sunshine may burn these wet areas of the plant. Do not water the leaves of your basil plants. Hold the water low, and aim the stream at the soil and at the base of the plants.

Treatment

• When brown or black discoloration damages the leaves, it's an indication of problem such as a lack of nutrients due to soil deficiency, burning or disease. The treatment for these problems is always the same: prune away all damaged areas of the plant. Use proper watering practices and regular fertilization to prevent future problems.