Orchids, with their exotic blooms and incredible diversity, are captivating plants for the home. Many growers find them difficult because they are mostly epiphytes, or “air plants,” naturally growing attached to trees or rocks rather than in soil. This unique lifestyle requires a fundamentally different approach to care. Their anatomy is designed for rapid water absorption and constant air circulation, making them vulnerable to standard houseplant practices.
The Unique Demands of Orchid Roots
The challenge in orchid care centers on the root system. Unlike terrestrial plants, epiphytic orchid roots primarily anchor the plant and absorb moisture and minerals from the air and intermittent rainfall. These roots are covered in the velamen, a spongy, white layer of dead cells that rapidly soaks up water.
This specialized structure means traditional potting soil is fatal to most orchids. The velamen requires constant exposure to air; when planted in dense soil or saturated media, the roots quickly succumb to rot because they cannot breathe.
To mimic their natural environment, orchids must be potted in coarse, chunky, and fast-draining media like fir bark, sphagnum moss, or lightweight expanded clay aggregate (LECA). The goal of this medium is to provide pockets of air around the roots. Watering involves thoroughly drenching the medium and then allowing it to dry almost completely before watering again.
Specific Atmospheric Requirements
Successfully growing orchids indoors requires replicating their native environment. A major requirement is high humidity, typically between 40% and 70%. Low home humidity, especially during winter, causes the velamen root layer to dry out too quickly, leading to desiccation and wrinkled leaves.
Strategies to increase moisture include grouping plants together or placing the pot on a humidity tray filled with pebbles and water. Air movement is also necessary, as high humidity without circulation creates a stagnant environment where fungal and bacterial diseases thrive, leading to spotting and rot.
Light is another sensitive factor, with most orchids, such as Phalaenopsis, preferring bright, indirect light. Direct sunlight can scorch leaves, while insufficient light is the most common reason a healthy plant fails to bloom. Many orchids also need a temperature differential, requiring a drop of approximately 5 to 10 degrees Celsius between day and night temperatures to trigger flowering.
Specialized Nutritional and Repotting Needs
Orchids have nutritional requirements different from standard houseplants. Since their roots are not in nutrient-rich soil, they require frequent, diluted feedings that mimic the low-nutrient wash received from rainfall in the wild. This philosophy is summarized as “weekly, weakly,” applying a highly diluted fertilizer solution with nearly every watering during active growth.
Standard houseplant fertilizers are often too concentrated and can cause salt buildup that burns sensitive orchid roots. Growers typically use a balanced fertilizer diluted to one-quarter or one-eighth strength. Monthly flushing with plain water is necessary to prevent the accumulation of mineral salts within the porous potting medium.
Routine repotting is another specialized maintenance factor. Orchid potting media, particularly bark, is organic and decomposes over one to two years. As the medium breaks down, it loses its chunky structure and holds too much moisture, leading to root rot. Repotting is a preemptive necessity.
The best time to repot is when the plant is actively growing new roots. During repotting, any dead or rotting roots must be carefully trimmed away. Aerial roots should be handled gently and either tucked into the new medium or left to continue growing outside the pot.