What Causes Plant Leaves to Turn Black?

Over-watering

• Excess water around the base of a plant prevents its roots from absorbing oxygen from the soil and carrying it to different parts. Roots that are left standing in water for prolonged periods develop root rot, a condition that causes them to turn black, slimy and emit an unpleasant odor. Lack of oxygen in the leaves increases plant stress, causing the foliage to gradually turn black. The problem is exacerbated when the plant grows in poorly-draining soils that retain moisture. To overcome the problem, water the plant until evenly moist instead of flooding it. If possible, transplant the plant to a spot with well-draining soil that prevents root rot and other problems associated with overly-moist soils.

Under-watering

• Similar to over-watering, under-watering a plant causes its foliage to turn black and dry. A plant that is not watered frequently dehydrates and begins to wilt and discolor. In some cases it drops its older foliage in an attempt to preserve moisture for its younger leaves. The problem exacerbates in the summer, when prolonged sunlight exposure causes its foliage to appear scorched. Maintain regular irrigation practices to keep the soil from drying. Inspect the soil frequently to allow more than the top 1 to 2 inches to become dry.

Fertilizer

• Improper fertilizer practices are also responsible for black plant leaves. While nutrients promote healthy growth and development, feeding a plant more fertilizer than it needs causes excess salts to accumulate around its base. Salt buildup in the soil causes root and leaf burn and prevents roots from absorbing and carrying soil moisture and nutrients to the foliage, thereby increasing plant stress. Upon inspection, the soil around an over-fertilized plant is covered in a white, crusty layer. Always follow label directions for fertilizing your plant. If possible, use a fertilizer specifically formulated for the type of plant you are feeding.

Leaf Spots

• A number of fungal and bacterial leaf spots cause the foliage of indoor and outdoor plants to turn black. Although initial symptoms of the diseases differ, infected foliage turns completely or partially black over time. Prune infected parts of the plant with sharp, sterilized scissors and adopt good cultural practices to help the plant regain its natural vigor. Treat fungal diseases with a registered fungicide.