Cold Damage on Tropical Orchids

Symptoms of Cold Damage

• Symptoms of injury from plummeting temperatures include slowed growth, discoloration, fungal disease, lesions on leaves and water-soaked, wilting foliage. Because these problems can also be the result of other culprits, such as root rot, light stress and dehydration, it can be tricky to diagnose your orchid when it presents these symptoms. They typically appear a few days or more after freezing temperatures hit -- not during the cold spell. Some orchids don't even show signs of cold damage until spring, when the heat injures them after their adjustment to the long-term cold period.

Treating Injury

• Some cold damage is untreatable once it appears. For instance, if growth fails to initiate after winter injury, you'll have to wait until the next growing season to see improvement in your orchid's appearance. However, you can aid the healing process and minimize damage by moving your injured orchids to a slightly shadier spot when heat hits; this also prevents water stress as your orchids regain their health. Wait until new growth emerges to water and fertilize your orchids, encouraging them to grow and put down new roots to replace injured or dead ones.

Winter Temperatures

• Knowing the temperatures that damage tropical orchids can help you diagnose winter injury and ideally prevent it. Warm-growing orchids, such as the Phalaenopsis orchid, prefer temperatures no lower than 65 degrees at night, with higher temperatures by day. Meanwhile, intermediate orchids such as the Cattleya need temperatures between 55 and 65 degrees at night, and cool-growing orchids can tolerate temperatures as low as 50 degrees; Cymbidiums can even tolerate temperatures that drop to 28 degrees for brief periods of time. However, orchids can usually handle a few hours at lower temperatures without major damage, as long as they're not subjected to freezing temperatures for long.

Orchid Protection

• To protect your orchid from future cold damage, avoid watering it the day before you anticipate freezing temperatures. Dry roots and potting materials can help your orchid tolerate the cold. When the freezing temperatures arrive, water your orchids to keep them warmer than the outside temperature because groundwater is typically about 63 degrees. . You can also cover orchids to insulate them or move them indoors for the duration of the cold snap.