What's wrong with my begonia (with photos)

[kitchenplanner]

I've had an indoors begonia plant for a few months now, and it grows well. However, it sheds leaves all the time. I water it when the soil is dry, and it's next to a big north-facing window. But every week, the plant without fail sheds leaves.

I attach a photo of the plant, and what the leaves look like when they drop. What am I doing wrong?

Yellow leaves can indicate lack of nutrients or excess of water.

Do you feed/repot it ever? It looks like it's in a small pot so maybe has used up all the soil nutrients?

Do you not let it dry out enough between water and let the excess drain off rather than sit in the out pot?

I only water when the soil is dry. And when I say dry I mean bone dry. Maybe time to repot then - I got it a few months ago and haven't repotted yet.

Could it be they are too dry then?

I water a little bit more when it’s very hot or I get leaves dropping from my various plants.

How dry should the soil be then when I water it?

I’m not an expert. I just reckon that if I stick my finger down inside the soil it should be just dry by the skin of its teeth or almost dry. Not bone dry.

They can shed leaves to preserve the rest of the plant if they think water is scarce.

Is it having a net loss of leaves? Evergreen plants shed the oldest leaves as new ones are grown.

If it were winter I’d suggest the air was too dry next to that radiator, but presumably the radiator’s not on at the moment. Has it got red spider mite? - a pepper like dusting under the leaves made-up of hundreds of tiny yellowish brown mites

I’d report in a larger pot and with new compost. It’s probably drying out too quickly because the small amount of compost isn’t holding moisture for long enough. I’d also move it away from the radiator, won’t be good for it when it’s on.

That radiator is never on, and there's no sign of pests. I'll repot