Repotting orchids often raises questions about the thick, silvery-green structures growing outside the pot. These are known as “air roots” or aerial roots, and they differ significantly from the roots of traditional houseplants. An aerial root is a structure that develops above the potting medium. Understanding the biology of these specialized roots provides the definitive answer to whether they should be buried during repotting.
Why Orchids Grow Aerial Roots
The majority of common orchids, such as the popular Phalaenopsis or moth orchid, are epiphytes. This means they naturally grow on trees or other plants for support rather than rooting in the soil. In their native tropical habitats, orchids use aerial roots primarily to anchor themselves to bark high above the forest floor. These roots are naturally adapted to life exposed to the open air.
The specialized, spongy outer layer of the aerial root is called the velamen, a multi-layered sheath of dead cells. This structure functions much like a sponge, allowing the root to rapidly absorb rain, dew, and atmospheric moisture. The velamen also acts as a protective barrier, shielding the inner, living root tissues from excessive light and dehydration during dry periods. This unique adaptation allows the plant to efficiently capture resources available in its canopy environment.
The Risks of Burying Aerial Roots
Aerial roots should not be treated like the roots of a typical terrestrial houseplant due to their fundamental difference in function. Forcing them into a dense potting mixture introduces significant risks. Aerial roots are biologically adapted for high air circulation, requiring constant and rapid gaseous exchange to remain healthy.
Burying these specialized roots in a moisture-retaining medium essentially suffocates them. The velamen is designed to quickly absorb water and then dry out, so it cannot survive prolonged contact with moisture. This lack of ventilation quickly leads to the breakdown of the velamen and the development of bacterial or fungal infections, commonly known as root rot. The loss of these functional roots severely stresses the plant, hindering its ability to absorb water and nutrients.
Proper Handling of Aerial Roots During Repotting
When preparing to repot, carefully inspect the existing root mass, both inside and outside the pot. Only roots that are clearly dead, mushy, or completely shriveled should be trimmed away using a sterilized cutting tool. Healthy, firm aerial roots, regardless of their length or direction, must be left intact.
When settling the orchid into its new container, the goal is to leave the healthy aerial roots exposed. If flexible, newer aerial roots naturally align with the fresh potting medium, they may be gently guided into the pot. Never sharply bend, force, or compress any rigid or stubborn aerial roots into the pot opening.
Roots that resist being placed into the pot must be left exposed outside the container, as they are still functioning organs. After repotting, attention should turn to the environment surrounding these exposed roots to ensure they continue to thrive. Increasing the ambient humidity around the orchid, perhaps with a humidity tray, is beneficial. Lightly misting the exposed roots can also provide the brief hydration they are adapted to absorb.