Orchids that grow on trees, known as epiphytic orchids, are distinct from their soil-dwelling counterparts. In their natural habitats, these orchids thrive by attaching themselves to tree bark, absorbing moisture and nutrients from rain, dew, and decaying organic matter collecting around them. While this environment provides some sustenance, it often falls short of what cultivated tree-mounted orchids require for optimal growth and flowering. Supplementing their diet through fertilization becomes an important practice to ensure their health.
Understanding Tree-Mounted Orchid Nutrition
Epiphytic orchids have evolved unique root systems, characterized by a spongy outer layer called velamen, which efficiently absorbs water and dissolved nutrients. In the wild, these plants obtain minerals and organic compounds from rainfall, dust particles washed from the air, and the slow decomposition of organic debris such as fallen leaves and bark accumulating in tree crevices or on branches. This natural nutrient supply is dilute and inconsistent. When cultivated on trees, their access to these sources is limited, making supplemental feeding necessary. Unlike soil-rooted plants, tree-mounted orchids rely on what they extract from the air and water, necessitating controlled nutrient delivery.
Choosing the Right Fertilizer
Selecting fertilizer for tree-mounted orchids involves considering nutrient composition and form. Water-soluble formulations are preferred for easy dilution and application to the orchid’s roots and mounting material. A balanced NPK (Nitrogen-Phosphorus-Potassium) ratio, such as 20-20-20 or 15-5-15, is recommended for general growth.
For orchids grown on bark, a higher nitrogen fertilizer, like a 30-10-10 ratio, is beneficial because bark decomposition by microbes consumes nitrogen, making less available for the plant. As the orchid approaches its blooming phase, switching to a fertilizer with a higher phosphorus content, such as 10-30-20, encourages flower spike development. Beyond NPK, the inclusion of trace elements like calcium and magnesium is important for orchid health. Urea-free fertilizers are suggested for epiphytic orchids, as urea nitrogen may not be as readily available in soilless media as nitrate nitrogen.
Application Techniques for Tree-Mounted Orchids
Proper fertilizer application is important to prevent damage to tree-mounted orchids. Dilution is a consideration, as orchids are sensitive to strong fertilizer concentrations. A common guideline is “weakly, weekly,” which means frequent application of diluted solution. Dilute liquid fertilizer to 25% to 50% of the recommended strength on the product label. If the label suggests one teaspoon per gallon, use one-quarter teaspoon per gallon.
Before applying fertilizer, thoroughly water the orchid. This pre-watering hydrates the roots, especially the velamen, and helps prevent root burn from concentrated fertilizer salts. The goal is to ensure the roots are receptive and protected.
Application methods for tree-mounted orchids involve spraying or drenching. Using a pump sprayer or hose-end sprayer enables even distribution over the entire root system and mounting material. When spraying, ensure the solution saturates the roots until it drips off. For drenching, the orchid can be gently soaked in a bucket of diluted fertilizer solution, ensuring all exposed roots are submerged for a short period.
This method is practical for smaller, easily accessible mounts. Target the roots directly, rather than just the leaves, as the roots are the primary uptake organs for nutrients. Avoid fertilizing during the hottest part of the day to minimize evaporation and leaf burn.
Slow-release fertilizer pellets can also be used, placed in small sachets or bags tied near the orchid’s root system. Each time the orchid is watered, a small amount of nutrients is released. This method is convenient for larger collections or those who prefer less frequent liquid applications. However, monitoring the release and ensuring even distribution is challenging.
Fertilization Schedule and Best Practices
The frequency of fertilization for tree-mounted orchids aligns with their growth cycle. During periods of active growth, spring and summer, fertilize every one to two weeks. As the orchid enters its dormancy phase, fall and winter, reduce fertilization to once a month or pause altogether if no new growth is observed. This adjustment prevents nutrient buildup when the plant’s metabolic rate slows.
Regular flushing of the orchid’s roots and mounting material with plain water prevents fertilizer salt accumulation. Salt buildup appears as a whitish or brownish crust and leads to root burn, inhibiting water and nutrient absorption. Flushing involves running plain water through the roots until it drains freely, or soaking the mount in clean water for 5 to 10 minutes. Flushing is recommended monthly, or every fourth watering, especially if using a “weakly, weekly” schedule.
Observing the orchid for signs of over-fertilization or under-fertilization is key. Symptoms of over-fertilization include poor root growth, dead root tips, brown or black roots, yellowing leaves, or a crust of fertilizer salts on the mounting surface. If these signs appear, cease fertilization and flush the roots thoroughly with plain water to remove excess salts. Conversely, slow growth or a lack of vigor indicates under-fertilization, requiring an increase in frequency or slight adjustment to dilution. Avoid fertilizing orchids that are dry, stressed, or newly repotted, due to increased root susceptibility to damage.