Why are the leaves on my orchid plant turning yellow?

On indoor orchids, one oldest lower leaf turning yellow can be normal, but several yellow leaves usually mean the roots, light, temperature, pests, or a recent product have stressed the plant.

Answer what you can see

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Push a finger two inches into the soil. What does it feel like?

Which leaves are affected?

Where does it live?

How fast did this happen?

Several causes can share the same answers: an old lower leaf, dry roots, pests, and salt damage can all fit yellowing over weeks, while even yellowing can fit wet roots, pests, or fertiliser damage; use the confirm checks to separate them.

The causes in full

Wet roots from frequent watering, poor drainage, or old bark mixMOST COMMON

How to tell
Check whether the bark is still soggy or wet in the middle of the pot several days after watering, and whether the visible roots are still green rather than silvery-white, the pot has no open drain holes, or the bark has broken down into dense, sour-smelling crumbs.

What to do
If the bark is soggy or wet in the middle of the pot, empty any outer pot or saucer, keep the orchid warm in bright indirect light, and do not water again until the bark has dried through and the visible roots have turned silvery-white rather than green -- the rule for Phalaenopsis and other orchids in coarse bark, while slipper orchids (Paphiopedilum) and thin-rooted types in finer mix should stay lightly moist and must not dry through. If the bark is collapsed or the roots you can see are brown and hollow, repot into fresh orchid bark in a pot with open drainage holes.

Normal ageing of one oldest lower leafCOMMON

How to tell
It is likely normal if just one lowest leaf yellows evenly while the rest of the plant is firm and new roots or a new leaf are still growing.

What to do
Leave the yellowing leaf until it loosens, or remove it only when it comes away easily. Keep normal care, and water only when the bark has dried through and the roots look silvery-white, using the medium-and-roots rule above.

Roots kept too dry for too longCOMMON

How to tell
The pot feels very light, the bark is dry right through, and the roots look silvery-white and wrinkled or flat rather than plump and green.

What to do
If the bark has dried through and the roots look silvery-white, using the medium-and-roots rule above and the pot is very light, water thoroughly until water runs out of the drain holes; if bark has become hard to re-wet, soak the inner pot for 10 to 15 minutes, then drain completely. Do not repeat this until the bark has dried through and the roots look silvery-white, using the medium-and-roots rule above again.

Window stress from direct sun, heat, cold glass, or draughtsCOMMON

How to tell
Suspect this when the yellowing is mainly on the side facing the window, especially if that leaf gets hot in sun, touches cold glass, or sits in a cold draught.

What to do
Move the orchid out of direct sun through glass and away from cold glass or draughts, but keep it in bright indirect light. If the bark has dried through and the roots look silvery-white, using the medium-and-roots rule above, water normally; if the bark is still damp inside or the roots are still green, do not add water just because the leaf is yellow.

Fertiliser salt burn or recent spray damageLESS COMMON

How to tell
Look for yellow or tan tips, patches on the newest growth, a white crust on the bark or pot, or yellowing that began soon after feeding, leaf shine, cleaner, or another spray was used.

What to do
Stop using the product that preceded the damage. If the bark has dried through and the roots look silvery-white, using the medium-and-roots rule above, flush the pot with plain room-temperature water and let it drain fully; after that, use only a weak orchid fertiliser on an already-watered plant.

Pests: spider mites, mealybugs, or scale insectsLESS COMMON

How to tell
Use a magnifier to check leaf undersides, leaf joints, and flower stems for fine webbing, cottony white clumps, or small brown raised shells that can be scraped off.

What to do
Move the orchid away from other plants, remove visible insects with a cotton swab, and use a pest treatment labelled for orchids and for the pest you found, following the label timing. Do not change watering unless the bark has dried through and the roots look silvery-white, using the medium-and-roots rule above.

Will it recover?

Yellow orchid leaves usually will not turn green again, so recovery means the yellowing stops and new leaves and roots grow healthy.

Stopping it happening again

Grow the orchid in a pot with open drainage and fresh orchid bark, keep it in bright indirect light away from hot sun and cold draughts, inspect for pests, fertilise weakly, and water only when the bark has dried through and the visible roots have turned silvery-white rather than green -- the rule for Phalaenopsis and other orchids in coarse bark, while slipper orchids (Paphiopedilum) and thin-rooted types in finer mix should stay lightly moist and must not dry through.