Orchid Leaf Damage in Unconventional Potting: Diagnosis

Leaf Underside Damage in Wire Basket with Glass Pebbles

Douglas bought two orchids, repotted in wire baskets with glass pebbles. Theory: wire allows airflow/light to roots; glass pebbles transparent for root photosynthesis. Waters every other day (dry in 6 hours), baskets drain seconds. Roots green/plump. Questions: 1) Underside of leaves on one plant has clustered dents growing in size, no inner flesh, no insects. What is it, how prevent spread? 2) Uses 20-14-13 nitrate nitrogen fertilizer (no urea), diluted weak (1/8 tsp/gal) due to frequent watering. Package says 1 tsp/gal every 14 days. Potential problem? Feed less often?

Expert Response

Douglas, more info helpful. Growing outside? If not, where? Sunlight? Assuming Phalaenopsis. If not, need type. When noticed after purchase? May be pre-existing. No problem with watering/feeding frequency/dilution. Expanding condition on leaf underside: possibilities: mesophyll collapse (sudden temp change from cold water or focused sun)—often first on top surface. Toxic buildup of fertilizer components—unlikely short-term. Fungus infection pre-purchase. If other leaves, cut below affected area with sterile blade to prevent spread. Seal wound with sulfur/powdered fungicide. Water early day.

Follow-Up: Phalaenopsis Indoors, Condition Details

Douglas: Phalaenopsis, purchased 3 months ago flowering. Spike cut. Indoor, well-lit room 6 ft from window. Condition likely post-purchase. Rules out mesophyll collapse (room temp water, no direct sun). Mentions toxic buildup possible but also says unlikely. Asks: if fertilizer toxicity, reversible by stopping fertilizer? If fungus, hates cutting leaves (only 4 affected, newest robust leaves).

Second Response

Douglas, unlikely toxicity (long-term). Some growers rotate fertilizers to reduce chemical toxicity. Doubt damage reversible. Best: prevent spread. Try Dynagrow ProteK in watering/feeding—strengthens leaf tissues; follow directions carefully (too much makes leaves brittle). Also repeated fungicide applications to affected areas. Prefer copper-based (Kocide). If fungus-related, limits spread via sporulation. Try this double approach.