What Causes Leaves on Houseplants to Turn Black?

Watering

• Improper irrigation practices cause the foliage of houseplants to turn black. While over-watering causes its roots to rot and the leaf tips to turn black, under-watering causes the leaves to appear dry and scorched, especially if placed in a warm spot with full sunlight exposure. Although the irrigation requirements of houseplants differ, water the plant frequently so the soil remains evenly moist at all times, and do not allow more than the top 1 to 2 inches of soil to dry. For each plant, use a pot in proportion to its root ball size, and fill it with nutrient-rich, well-draining mix. Ensure the pot has adequate drainage holes, or drill holes if necessary, before planting.

Fertilizing

• Similar to outdoor plants, houseplants also require fertilizers for their growth and development. Because the roots of potted plants are confined in a container, fertilizer dosage rates are less than those for outdoor plants. Over-fertilizing a houseplant causes excessive salt buildup in the soil that eventually causes the foliage to turn black and appear burnt. Upon inspection, plant containers have a white crusty layer along the sides or on the soil surface. Douse the potted plant with water once a month until excess water seeps out of the drainage holes, along with fertilizer salts. Always follow label directions when feeding your houseplants.

Bacterial Leaf Spot

• Bacterial leaf spot (Pseudomonas spp.) is a disease that causes black leaves on houseplants. Initial symptoms include yellowing marks on the lower leaf surfaces that gradually develop into long red streaks. The streaks deepen in color and gradually turn black, while the leaf tissue around them discolors and turns yellow. Prune infected parts of the plant with sharp, sterilized pruning scissors. Place the plant in a spot that best meets its sunlight requirements, and space multiple houseplants sufficiently apart to prevent overcrowding.

Fungal Leaf Spot

• Fungal leaf spot is also responsible for black leaves on houseplants. Initial symptoms of the disease include tiny black spots on the leaves. Left untreated, the tiny spots gradually merge with surrounding spots to form patches that cover the entire leaf surface. Leaves with large patches fail to perform photosynthesis, eventually turn yellow or brown and fall off. Adopt good cultural practices to reduce chances of your houseplant contracting the disease. Prune infected parts with sharp scissors and apply a registered fungicide over the plant to prevent the disease from spreading.