Answer: Oxalis, or woodsorrel, is resistant to glyphosate, the active ingredient in Round-Up. But your orchids would be highly susceptible to it. I'd suggest hand-pulling the weeds to preserve the health of your plants. Oxalis can spread through seeds and underground rhizomes, so keep the weeds pulled before they flower and set seed, and before the roots can get too firmly established. If the infestation gets out of hand, you may have to repot your orchids in fresh growing medium to eliminate all roots and seeds. If you do, be sure to place a thick layer of bark chips on the soil to keep weed seeds from getting a foothold.
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