Trimming orchid roots is a common dilemma for orchid owners, especially when repotting. While it might seem intuitive to clean up the root ball, the general rule is to be highly conservative with pruning. Orchid roots are specialized organs necessary for the plant’s survival and health. Indiscriminate trimming can cause serious harm, but unhealthy roots must be removed to prevent disease from spreading.
The Role of Healthy Orchid Roots
The roots of epiphytic orchids, like the popular Phalaenopsis, are uniquely adapted to growing on trees. These roots are covered in a spongy, multi-layered tissue called the velamen. The velamen acts like a natural sponge, rapidly absorbing rainwater and temporarily storing moisture and nutrients before passing them into the root’s inner core.
The appearance of a healthy root system indicates the plant’s hydration status. When dry, the velamen is filled with air, giving the roots a firm, silvery-white or pale green appearance. After watering, the roots become plump and turn a vibrant green color as the velamen absorbs water, allowing the chlorophyll-containing cells beneath to show through.
Both roots growing into the potting medium and those growing outside the pot, known as aerial roots, are healthy and functional. Aerial roots should be left intact, as they absorb atmospheric moisture and contribute to photosynthesis. Only visibly compromised roots, regardless of their location, should be considered for removal.
Identifying Roots That Require Pruning
Pruning should only occur when the plant is removed from its pot, typically during repotting, allowing for a thorough inspection of the root ball. Only three categories of roots should be targeted for removal, as they are no longer viable or pose a threat to the plant’s health.
Dead Roots
Dead roots have completely dried out and shriveled. They feel dry, papery, and brittle to the touch. Often, the outer velamen layer peels away, leaving behind the thin, wiry inner core (the central vascular cylinder). These dried-out remnants should be removed completely.
Rotted Roots
The second and most concerning type is the rotted root, usually caused by overwatering or poor drainage. Rotted roots appear dark brown or black, and feel soft, mushy, or slimy when gently squeezed. If the root has lost its turgidity and is flat, it is no longer functioning and must be removed.
Infected Roots
The third category includes roots showing signs of fungal or bacterial infection, often presenting as discolored, deteriorating tissue. Trim these infected roots back until only firm, healthy tissue remains to halt the spread of the pathogen. Removing all non-viable tissue prevents it from becoming a breeding ground for harmful organisms.
Essential Tools and Technique for Trimming
Before beginning pruning, prepare your tools to ensure the health of the plant. Use a sharp, clean cutting instrument, such as a razor blade or bypass pruners, to make clean cuts without crushing delicate root tissue. Sterilization is necessary to avoid transferring pathogens between plants or from an infected root section to a healthy one.
To sterilize the cutting tool, wipe the blade thoroughly with rubbing alcohol or a 10% bleach solution. After each cut into diseased tissue, quickly re-sterilize the blade before making the next cut into the healthy root system.
When trimming, make a precise cut into the root just above the point where the tissue becomes firm and healthy. Do not attempt to save any part of the mushy or dry portion, as it has lost its ability to absorb water and nutrients. After all compromised roots are removed, apply a light dusting of cinnamon powder or horticultural charcoal to the fresh cuts. This acts as a natural antifungal agent and temporarily seals the wound before the orchid is repotted into fresh, well-draining media.