There are many retailers, even Bonsai Shops that will sell you “Indoor Trees.” Think about that for a second. How is that truly possible?
Trees were here before us so how did they grow indoors before we came around? But all kidding aside, all trees including all Bonsai trees should live outside. To thrive and survive for a very long time there is no substitute. No quality of equipment or amount of care and money can change that.
The atmosphere, and Nature in general is all a tree needs. And don’t forget water. That is another topic all together. But back to “indoor trees.”
It is true that with some trees, depending on your climate, (mostly tropical trees) you have to take them indoors during winter to protect them from freezing. However, the rest of the year they should be outside.
Keep in mind this is if you are growing them out of their natural climate. Hence having to take them indoors. If you grew tropical Bonsai in their natural climate, then they can stay outside all year. Keep in mind that in Bonsai we battle Mother Nature all the time.
On the same note, keeping a Japanese Maple while living in the tropics will require you to refrigerate the tree for a specific number of chill hours during winter. The tree has to go into dormancy or it will not have enough energy to survive. Trees too must sleep in some cases.
However, I can promise you that a Maple kept in the tropics will not be healthy or thrive. It will make it a few seasons, maybe. Ultimately though, you will lose the tree.
Same thing with keeping any Bonsai indoors all the time. Even if it is tropical. The humidity is not right inside, lighting, air flow, beneficial critters, etc. Tropical trees will last inside for a while but again, they will never be truly healthy or vigorous and ultimately will lose steam.
Many will disagree, but the fact that all trees come from the outdoors, and that is what is best for them, cannot be argued. If you want a healthy tree with a great shot at reaching it maximum potential, keep it outside.
If your tree is happy, you are happy.