Q:

Is waking up a plant or a tree in winter harmful for it?

As it is winter, even by keeping my bonsai Zelkova indoors, it losts most of its leafs. For a week or so, I let it outside during the day for it to take the sun.
Now, it's already producing new leafs.
Is it harmful for the tree to not let it "sleep" in winter and to have it produce leafs all year long? Can it be exhausting for the tree?

A:

Japanese elm is a deciduous tree and, as such, it expects to lose its leaves and become dormant during  winter. It is an outdoor bonsai, but may be susceptible to frost damage when the weather is very cold because of its shallow root system and container, so is best moved to a cold greenhouse or somewhere that isn't warm, but frost free. It's not good to keep it in a heated environment during winter, which it sounds like you're doing. If you can find somewhere unheated but frost free with daylight, move it there instead. Further information here https://www.bonsaiempire.com/tree-species/zelkova

