Short answer
Leaves falling off a Moth Orchid (Phalaenopsis) are usually caused by advanced crown rot resulting from overwatering or water trapped in the leaf crevices. The most common fix is to stop all watering, remove the plant from its pot to inspect for rotted roots, and ensure the crown remains dry at all times.
When a Phalaenopsis begins dropping leaves, it is often a sign of significant stress at the plant's core. While the loss of a single, older leaf at the very base is often a natural part of the orchid's aging process, the loss of multiple or younger leaves indicates a serious issue with root health or environmental management.
Crown rot occurs when water accumulates in the center of the leaf rosette, creating a breeding ground for bacteria or fungi. This causes the stem to turn mushy and leaves to detach easily at the base.
Check: Check if the center of the plant or the base of the fallen leaves feels soft, mushy, or smells foul.
Fix: Remove all mushy, black, or decaying tissue with a sterile blade, sprinkle cinnamon on the wound as a natural fungicide, and keep the foliage completely dry.
Orchids are epiphytes that need air around their roots; when the potting medium decomposes or stays perpetually wet, the roots drown and die. Without functional roots to uptake moisture, the plant will shed leaves to conserve energy.
Check: Unpot the orchid and check for dark, mushy, or hollow roots rather than the firm, green, or silvery-grey roots of a healthy plant.
Fix: Repot the orchid in fresh, chunky orchid bark, trimming away all dead, brown roots with sterilized shears.
If the orchid is kept in a drafty area or receives too much direct sun, it can lose water faster than the roots can supply it, causing leaves to limp and eventually abscise. This is more likely to happen if the roots have already been compromised by underwatering.
Check: Observe if the aerial roots are thin, shriveled, and light grey or brown instead of plump and green.
Fix: Ensure the plant is in bright, indirect light and maintain a consistent watering schedule where you soak the roots thoroughly before letting the medium dry out.
When to worry
If you notice the main stem turning dark brown or black, or if multiple leaves are falling off within a few days, the plant is likely in a terminal state of rot and requires immediate emergency repotting.
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Diagnose my Moth OrchidYes, it is perfectly natural for Phalaenopsis to shed their oldest, bottom-most leaf occasionally. This is only a concern if the leaf turns yellow or mushy very rapidly or if multiple leaves begin to drop.
Do not remove yellowing leaves until they are completely shriveled and detached, as the plant may still be reabsorbing nutrients from them. Cutting into healthy green tissue provides a new entry point for infection.
You can use a specialized orchid fungicide if you suspect fungal crown rot, but physical removal of the decayed tissue and ensuring proper airflow is significantly more effective.
Consistent with guidance from: American Orchid Society, Royal Horticultural Society.