Originally, Bonsai were always kept outdoors, and the early gardeners grew only the types of trees that would be able to live in their climate. Thus, people in southern China or Japan would only be growing tropical or temperate trees, whereas gardeners in the northern areas would grow trees that could take frost, and even heavy snowfall.
We in America are, in a sense, pioneers of a new art form, that of growing Bonsai indoors. Our growing conditions shouldn’t discourage us, but rather allow us to find new and innovative ways of keeping the trees healthy indoors.
Indoor conditions are very different from outdoor ones, of course: light, temperature, moisture of air, air circulation, and day-to-night temperature changes are all quite different from "natural" ones.
Q: How much light do Bonsai need?
A: Light is essential for keeping plants healthy.
Bonsai need full sunlight and good ventilation. Most varieties require at least two hours of direct sun each day. Never place them in a poorly lit area!
Universally, Bonsai like good amounts of direct sunlight. That’s a starting point for deciding on proper placement for your trees.
When the trees are inside, make sure they get good, strong sun for at least a couple of hours every day. Light intensity is reduced considerably by window glass, and if the tree is in a poorly lit area, it will not do well.
If light is not adequate, over watering becomes a danger as well, because the tree will dry out a lot more slowly.
Since plants photosynthesize nutrients from sunlight, strong sun will result in smaller leaf size as well, since the foliage does not need to expose as much of it’s surface area to the light for adequate nourishment. And of course, small, compact foliage is what we want to produce! Consider getting a good grow lamp such as an OTT light which will simulate the natural spectrum of the sun.
Q: Are there any trees that can be grown in low light?
A: There are some, but it’s certainly important to get your trees as much light as you can. Some of the plants that are grown in low light tend to be larger-leafed varieties; such as the arboracola they will never have the compact growth that they would have in good light.