Why are my orchid leaves turning yellow?

Phalaenopsis orchids most often get yellow leaves from overwatering. Constantly wet bark suffocates the roots, they rot, and the starved plant yellows its leaves from the bottom up. The next most likely reasons are natural shedding of the oldest lower leaf, then too much direct sun, with underwatering and cold shock less common. Check the roots through the pot first, then ease off watering.

Most likely cause

Overwatering is the top cause of yellow orchid leaves. Phalaenopsis are epiphytes that cling to tree bark in the wild, so their thick roots need air and a dry-out between waterings; sitting in soggy media starves them of oxygen and they quickly rot and stop feeding the plant.

You can confirm it by looking at the roots and the pattern. Healthy roots are plump and silvery-green or white; rotted ones are brown, soft and stringy, and the lower leaves yellow and feel limp rather than crisp. If the bark is still wet days after watering, or the pot has no drainage, this is almost certainly the driver. Repot into fresh dry bark, trim mushy roots, and let it dry properly between waterings.

Other causes

These rank below overwatering but can overlap with it.

Natural aging. A single oldest bottom leaf slowly yellows while the rest of the plant looks healthy and the roots are firm; this is normal and needs no action.
Too much direct sun. Harsh light scorches the foliage; look for yellow or bleached patches, sometimes with brown sunburn spots, on the side facing the window.
Underwatering. Dehydration shrivels the roots; they look grey and flat, the leaves go limp and leathery, and the bark is bone dry well past a normal watering gap.
Cold draught or shock. A sudden chill near a window or air-conditioning vent can yellow leaves; the change follows a cold snap or a recent move.

How to fix it

Inspect the roots. Slip the plant from its clear pot and check for firm, green roots; brown, soft, hollow roots confirm rot.
Trim and repot. Cut away mushy roots with a sterilised blade and repot into fresh, dry orchid bark in a pot with drainage holes.
Water correctly. Water only when the roots turn silvery and the bark is nearly dry, usually every 7 to 10 days, then let it drain fully.
Empty the saucer. Never let the pot stand in collected water, which keeps the roots wet and rotting.
Fix the light. Move it to bright indirect light, out of direct midday sun that scorches leaves.
Shelter from draughts. Keep it away from cold windows, doors and air vents, ideally between 18 and 27 degrees Celsius.
Leave aging leaves alone. Let a naturally yellowing lower leaf detach on its own instead of cutting it.

Cause	Tell-tale sign	Fix
Overwatering	Soft yellow leaves, brown mushy roots	Repot in dry bark, water less
Natural aging	Single oldest bottom leaf only	Let it drop on its own
Direct sun	Bleached patches facing window	Move to bright indirect light
Underwatering	Limp leaves, grey shrivelled roots	Water thoroughly, then keep cycle
Cold shock	Yellowing after a chill or move	Keep warm, away from draughts

Frequently asked questions

Do yellow orchid leaves turn green again?

No. Once a Phalaenopsis leaf turns yellow the chlorophyll is gone and it will not recover its colour. Focus on fixing the cause, and let a fully yellow lower leaf drop on its own rather than forcing it.

Is it normal for the bottom orchid leaf to turn yellow?

Yes. A Phalaenopsis sheds its oldest lower leaf from time to time as it pushes new growth from the top, which is normal aging. Several leaves yellowing at once, or an upper leaf going yellow, points to overwatering or sun instead.

Should I cut off a yellow orchid leaf?

Usually no. A naturally aging lower leaf will yellow, soften and detach cleanly by itself, which protects the plant from open wounds. Only remove a leaf if it is mushy and clearly rotting, using a sterilised blade.

Can overwatering turn orchid leaves yellow?

Yes, and it is the most common cause. Soggy bark suffocates and rots the roots, so they can no longer feed the plant and the leaves yellow, often turning soft. Check that the roots are firm and green, not brown and mushy.

Why is my orchid leaf yellow but the roots look fine?

Yellowing with healthy silvery-green roots is usually natural aging of the oldest leaf, or too much direct sun. Check whether only the bottom leaf is affected, and whether the plant sits in harsh midday light, then adjust its position.

How do I stop my orchid leaves from turning yellow?

Water only when the roots turn silvery and the bark is nearly dry, usually every 7 to 10 days, and never leave water in the pot or saucer. Keep the orchid in bright indirect light and away from cold draughts.