Phalaenopsis orchids are among the easiest orchid species to grow at home, but do need a little special care. Also called moth orchids, these plants naturally grow on the branches of trees, and require special soilless orchid mix and some careful treatment. Like all plants, Phalaenopsis orchids may suffer from diseases and other problems, including brown-spotted foliage.
Several species of fungus cause brown spotting on orchid leaves. These spots often start small, but continue to enlarge over time. In severe cases, the orchid may lose its leaves. To treat this problem, remove all leaves that show spotting and destroy them. Then, treat the problem plant with fungicides. Allowing the damaged leaves to remain increases the risk of reinfection.
Phalaenopsis orchids like bright, indirect sunlight, but may suffer burnt and damaged leaves in strong, direct light. Sunburn causes dark brown or blackened patches on the leaves. Unfortunately, there’s nothing you can do to heal this kind of damage once it’s there, but moving the plant to a shadier location will prevent future burns. If the sunburn seriously affects the look of the plant, remove burnt leaves a few at a time. Don’t overdo it if much of the plant suffers from spotting, however. The leaves are your orchid’s food source, and removing too many could weaken the plant.
Orchids prefer warm temperatures – above 70 degrees during the day. Too much cold can discourage growth and even cause chill damage. This damage appears as yellow or brown sunken spots on the leaf surface. As with sunburn, there’s not much you can do about cold damage after it occurs. Prevent the problem by keeping your orchids in a temperature-controlled environment.
Orchids may also develop brown-spotted foliage from a nutritional imbalance. Brown spots may indicate too little iron, too much manganese, or too much zinc. Iron deficiencies usually occur in high-pH conditions, while excessive manganese usually happens in very acid conditions. Adjusting the pH of the potting medium or supplementing the plant usually fixes these problems.