This is my first bonsai. It's a Chinese Elm that I've had for a little under a year. I live in London, UK. It is situated in a bedroom with a roof window and a dedicated LED desk light that is on all day to try compensate for the limited amount of light coming through (see setup below). It's watered with a watering can until the water flows to the bottom plate.
Here's the issue: it goes through repeated cycles where it loses all its leaves, grows them back, only to lose them again after 3 weeks. It started at the end of fall last year and has happened about 4 times now:
I've tried to change the feed regimen, water more often (but then some mould started appearing at the surface). I've also tried an insecticide in this last cycle, it hasn't done anything.
My questions are:
- What problems result in cycles where the plant grows and loses its leaves repeatedly over a 3 week period?
- Before they fall, a lot of leaves are partly discoloured (see March 22 and 24 above). Is that a usable symptom?
- The LED is a normal desk light, does it need UV light?
It would be very appreciated if anyone had any theories that I could try. My setup is below for reference.