Orchids that produce aerial roots are called epiphytes. In nature, these roots help the plant anchor itself to trees. Often, epiphytic orchids produce aerial roots simply because it's what they do in nature. However, if the orchid has been in its container for very long, the plant may produce aerial roots because it is pot-bound. Aerial roots do no harm to the orchid. Orchids generally tolerate cramped conditions in containers, but under some conditions, the plant may need repotting.
Aerial roots contribute to the orchid's survival by gathering water and nutrients from the air. Aerial roots may be thick or thin. These white tendrils usually grow from the base of the plant, along the surface of the pot, but may emerge from between the leaves. The roots can lengthen enough to spill over the sides of the pot. As long as the roots are white or pale green, they are living tissue that helps the plant grow and thrive. Aerial roots contain chlorophyll and perform some photosynthesis duties as well.
Growing Medium Failure
Check the growing medium. If the mixture is old, it may have deteriorated to the point where it no longer supports the orchid properly. When the growing medium fails, it can become compacted around the orchid's roots, reducing the roots' ability to absorb moisture and nutrients. The plant puts out aerial roots as a survival mechanism. Try repotting the orchid in a slightly larger pot with fresh growing medium formulated especially for orchids. Do not cover the aerial roots in the growing medium, as they will probably rot. A study at the University of Michigan found that Phalaenopsis planted in a bark-based medium produced significantly more aerial roots than those planted in a mixture of peat and perlite.
Light and Water
Orchids need light to thrive, and their roots seem to need it too. Try repotting the orchid into a clear container to encourage the roots to stay put rather than escaping the pot to sunbathe. The University of Michigan study also found that Phalaenopsis and Doritaenopsis orchids produced fewer aerial roots when planted in clear containers. Mist the aerial roots whenever you mist the foliage, or place the pot in a shallow container filled with pebbles and water to increase humidity.
If any of the aerial roots become dry or are obviously dead, use sharp, sanitized cutters to clip off the root. Avoid injuring the plant when you prune away the dead material; cut close to but not even with the stem. Never cut living aerial roots off the plant, as this may shock the plant and cause wounds that allow diseases to invade the orchid.