Chinese Elm bonsai growing and losing its leaves every 3 to 4 weeks

Question

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.

Research if the plant can handle constant light. Locally, some trees have died due to strong 24hr lighting. I would limit to 20 hours per day. — Polypipe Wrangler, Mar 27 '21 at 09:59
Thanks @PolypipeWrangler, I didn't mean to say the light was on 24/7, just during daytime. — Cyril Le Roux, Mar 28 '21 at 11:18

score 1 · Answer 1 · answered Mar 26 '21 at 16:39

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I think your problem is the indoor climate. Maintaining bonsai indoors is very difficult and only some species (tropical) will work out. A Chinese Elm is from a temperate climate, so it is very hard to keep it alive indoors. If it is not too cold outside, I would advice to put it outdoors, and see if the leaves stay on. Good luck.

answered Mar 26 '21 at 16:39

benn

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It is quite normal for a deciduous tree to drop its leaves in winter and start to grow again in spring. The problem is that indoors it is too warm, so it immediately starts to grow more leaves, but also too dark, so they don't develop properly. In London it should be perfectly OK outside all the year round, unless you have some abnormally cold weather (i.e. temperatures below freezing all day, not just at night). – alephzero Mar 27 '21 at 03:34

Chinese Elm bonsai growing and losing its leaves every 3 to 4 weeks

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