Why does my moth orchid have brown soft patches on the leaves?

On a moth orchid this is a patch on a leaf that has turned brown to black, soft and wet, usually at the base of a leaf near the crown or where a drop of water has sat. It can spread inwards over a few days and may smell.

The most likely cause, as the entry says, is water left standing on a leaf or in the crown, followed by bacterial rot. The RHS says to take care not to splash the leaves or get water into the crown. Water in the crown has nowhere to go, and a moth orchid watered at a sink on a 7 day rhythm in the growing season gets a chance for this every time.

To confirm it in a minute, tip the plant and see whether water runs out of the crown. Look at where the patch is: a patch at the base of the leaf next to the centre, or a round one where a drop sat, fits this cause. Press gently: soft and wet is rot, and firm and dry is old damage. Check the air as well. Still, damp air makes it worse.

Two other causes are worth ruling out. Cold damage shows as soft patches on the side of the plant nearest the glass after a cold night or from cold water on the leaves. Sun scorch is bleached or papery patches on the leaves facing the window, and a leaf that was wet when the sun reached it burns where the drops sat. The NC State plant toolbox also lists botrytis spot on the flowers, which is a different thing.

Patches that are already there do not heal. What matters is whether new ones stop appearing and whether the rot reaches the growing point. If it does, the plant is lost, and otherwise the new leaves are the proof.

What this plant wants

The fix

Cut out the affected tissue with a clean blade, keep the leaves dry, and improve the air movement around the plant.

Read on

Brown soft patches on the leaves

The same sign on any plant, with the causes in the order they are likely.

Moth orchid care

Light, water, feeding, repotting and the rest of the entry.

Check it in the diagnoser

Opens with the plant, the part and the sign already chosen.