One Leaf Turning Yellow on an Orchid

Characteristics

• Orchids are members of the Orchidaceae family of plants, a group that contains about 25,000 species. Orchids tend to have insignificant foliage and intricate blossoms. Individual varieties have specific requirements, although most orchids grown as houseplants have similar needs. The majority of houseplant orchids require loose, loamy mediums that contain a high concentration of vegetative materials. Most require high levels of humidity, even moisture and adequate lighting. Occasionally, yellow leaves can be a sign of poor growing conditions.

Leaf Renewal

• As with other types of houseplants, orchids renew their leaves at regular intervals. A single yellow leaf is commonly a prelude to new leaf growth. The rate of leaf turnover depends on the cultivar. For instance, moth orchids, or Phalaenopsis, produce one or two new leaves each year. Old leaves turn yellow and gradually wilt, as the new leaves appear. This is the most likely reason for a single leaf that turns yellow while the rest of the plant remains healthy.

Sunlight

• Excess sunlight is another possible cause of yellow leaves in just one area of the plant, especially if you fail to rotate the plant regularly to provide even light exposure to the foliage. Most orchids produce leaves in light shades of yellow-green. High amounts of sunlight initially cause leaf yellowing on the exposed foliage. The yellow leaves later turn white. As the burnt areas of foliage dry out, the damaged leaves turn brown and fall from the plant. Prevent this problem by moving the orchid into an area with less light and rotate the plant one quarter-turn every time you water.

Disease and Pests

• Although diseases that cause orchid leaves to yellow normally affect numerous areas of foliage, a single yellow leaf may signal the beginning of a health problem. Common pests that may infest orchid plants include mealy bugs, aphids, mites and scale. Diseases that can affect orchid plants include fungal, bacterial and viral diseases. If the yellowing spreads to other leaves, examine the plant for signs of insects or areas of rot. Prompt treatment with an insecticide or fungicide can help keep the condition from spreading to areas of healthy foliage.