Leaftip Burn

Question

I’ve noticed the tips of the leaves of some of my orchids are brown, and guessed it was due to over-fertilizing. This morning, I discovered two small (not tiny) brown spots on a dendrobium leaf. The cane has at least seven to eight leaves, and the spotted one is top-most. By looking at the back of the leaf, I found the center of the brown spots became thinner than the leaf. Are the spots an indication of sunburn or fungus? I have the orchid at an east window, so it shouldn’t be receiving too much sun. —Elizabeth Hsu
 

Answer

The leaf-tip burn you describe is not unusual in orchids grown in the home or under very dry conditions, nor is it necessarily indicative of over-fertilizing, but rather of salt-related damage. This occurs when the salt concentration in the soil solution reaches a certain critical point, either through accumulation by over-dry conditions, or by the excess application of fertilizer. Keeping the plants more evenly moist, and flushing thoroughly with clean water can also help to reduce this sort of injury to orchids. I doubt that the symptom you describe on the top leaf is fungus, and even if it is, it sounds like a type that is the result of a secondary infection that is rarely more than a cosmetic problem. Unusually cold water can bruise the softer tissue of a developing leaf, making it susceptible to infection in the same way that a cut on your hand is liable to be infected. The infection usually stops on its own, leaving the type of lesion you describe. —Ned Nash