Causes of Fungus on a False Christmas Cactus

Irrigation

• One of the main causes of fungal rot is overwatering. Roots left to sit in soggy soil soften, allowing soil borne fungus into the root system where it can spread throughout the plant. According to the Arizona Cooperative Extension, false Christmas cactus should be watered thoroughly and then not watered again until the top half inch of soil is dry. Avoid wetting foliage. Splashing water can spread fungi.

Poor Growing Conditions

• Improper growing conditions also can cause fungal infections. Potting soil that is compacted or containers without drainage holes allow the buildup of salts and fertilizers that can contribute to the spread of fungal growth. Pythium rot is a problem in salty, overfertilized soils. Always use containers with drainage holes. Potting soil for false Christmas cacti should be sandy to allow for proper drainage and to give roots much-needed oxygen.

Overcrowding

• Many houseplant enthusiasts enjoy combining plants for aesthetic effect. Too many plants placed too closely together can be a problem. Some fungal infections, like powdery mildew, thrive in shaded, moist locations. Space plantings so that your false Christmas cactus gets good airflow and so that sunlight reaches all parts of the plant. Large plants can be pruned or moved to allow more space for your cactus.

Sanitation

• Often fungal infections are spread by unwitting gardeners themselves. Reusing old containers without washing them first can spread soil borne fungus. Using watering cans, pruning shears or spades without first sanitizing them also can spread pathogens. Plant debris, like dead leaves or flower petals, can harbor fungus and spread it to your false Christmas cactus and neighboring plants. Insects like fungus gnats can transmit disease as well. Keep your tools and containers clean and allow soil to dry in between waterings to control fungus gnats.