Yes they can be damaging - the really fine roots can infiltrate every last void in the medium, suffocating the otrchid roots.
I do some pulling every time I visit the greenhouse, but got smart about a year ago, and keep a bottle of premixed Round-Up herbicide and a cup full of cotton swabs out there.
Dip the swabs in the herbicide, "paint" the leaves of the oxalis (wihtout touching the orchid), and it will die in fairly short order.
|