My Purple Moth Orchid Has Black Stem Leaves

Disease Issues

• Fungal issues, particularly root rots, can cause black stem leaves in Phalaenopsis orchids. Verticillium rot and armicillia rot are the most common root rots and are encouraged by an overly moist environment. Leaf spot is a bacterial disease that can, cause the stem leaves to blacken over time. The most important factors that cause purple moth orchids to be vulnerable to infection are open wounds, infected soil, and overly moist growing medium.

Watering Issues

• Purple moth orchids are extraordinarily sensitive to excessive watering. This is because, unlike most orchids, purple moth orchids do not possess a bulb at their base that functions to store water. This means that when provided with too much water, the purple moth orchid does not have a biological mechanism to cope with this problem. The result is black stem leaves, if this condition continues over time.

Treatment of Black Stem Leaves

• If you suspect that your moth orchid has been overwatered, check the moisture level of the growing medium. If it seems too high, place the plant under a heat lamp for a short period of time, checking periodically to ensure that not too much water is being lost. The growing medium should not be bone dry. Do not water more than once weekly following this treatment. Prune leaves that show signs of leaf spot infection. If fungal disease is the issue, treat with the application of a fungicide.

Prevention of Black Stem Leaves

• The single best way to prevent most issues that cause black stem leaves in Phalaenopsis orchids is to refrain from overwatering. Spray regularly with a fungicide as additional insurance against rots and molds. To prevent bacterial infection, plant your purple moth orchids from sterile cuttings and use a sterile growth medium.