Despite the common misconception that Bonsai Trees belong to dwarfed species, these man-shaped trees grown in pots are just ordinary trees that have been trimmed and forced to grow as a miniature tree.
The key point here is trees. Not plants, not flowers, not plastic sculptures. Trees. And trees do not grow inside houses nor underground caves regardless of what Jules Verne told us about underground trees in Voyage to the Center of Earth.
Now what does a interior lack with respect to woodlands? Fresh air, maybe. Swarms of bees, I hope so. But for sure it lacks direct light shining from the sun all day long.
Even with an open space loft, the amount of sunlight entering the windows is limited by the exposure the bonsai tree has. With a northern exposure giving in the less amount of sunlight.
The simplest solution is to mimic the sun’s behaviour and rotate the tree. By turning it at regular intervals the direct light from the window will shine on your bonsai’s foliage allowing it to develop healthy branches all around.
This of course means you have to take in account yet another aspect of bonsai tree care, in addition to the already rigorous activities such as watering and pruning.
An alternative solution is to try the so called natural daylight lamps. This kind of lamps are quite pricey, as they are employed in phototherapy, literally the treatment of an illness by exposure to sunlight. Phototherapy lamps include all the spectrum of daylight, including some ultraviolet radiation and are popular in the alternative health niche. Using such a light does not have the adverse effects common incandescence light bulbs have -namely radiating only a narrow yellow-red spectrum of light.
However, you should check two important factors when choosing such a light. First, that it indeed is a sunlight-like phototherapy bulb. So called “daylight” fluorescent lamps found at department stores are typically 6400 Kelvin degrees and only resemble the daylight color temperature.
Further, the CRI, or Color Rendition Index, should be around nine to be effective. The CRI measures how precisely the lamp emits light, and is mainly of use in photo studios or printing agencies where proper color reproduction is mandatory. But it is essential for your bonsai’s health as well.
Now, if you go for the artificial daylight route, this does not mean you should not rotate the tree at all. Otherwise there will always be a marked difference between the side hit by direct sunlight and the one artificially lit. But you can reduce the rotation load and take a more relaxed approach, by making sure that, on average, all sides of the tree get an equal share of sunlight and artificial light.
One last tip: light from the sun does not decrease with distance. Or rather, it does but so slightly that on an earthly scale this decrease is considered to be negligible. On the other hand, artificial light decreases with the square of the distance.
Sounds complex? It isn’t: all that this means is that if you place your bonsai tree 1 meter or 2 meters away from the window, the amount of sunlight will be more or less the same. On the other hand, if it is placed two meters away from the artificial lamp, it will get one quarter of the light it would get being just one meter away.
So make sure to have it way closer to the lamps than to the window to level the amount of light exposure.