How to Use Artificial Light for Bonsai

In areas where outdoor bonsai are in storage from late fall to early spring, growing indoor bonsai has become more common. Artificial lighting can give your trees light during the winter, but taking plants indoors presents special problems. Heating outlets are sometimes located directly under windows, creating drafts of hot air that dry trees out. Incandescent bulbs also give off too much heat, which means you cannot place trees too close to those types of lighting.

What is the Best Artificial Light for Your Bonsai?

Fluorescent tubes, the coolest lighting available, are your best indoor light source. They are readily available and are also the least expensive to operate. Plants utilize the same rays from fluorescent tubes that they do from the sun. In terms of the color spectrum, the blue rays keep plants healthy and compact, and the red and the far red rays promote flowering.

Artificial Light for Bonsai Trees
image source: http://www.bonsaitreegardener.net/

There are several lengths of fluorescent tubes available, with the four-foot and eight-foot models being especially popular. All tubes lose a great deal of light output over time and need to be changed every year. Prices vary greatly. Some fluorescent “plant tubes” are expensive and do little more for plants than cool white (fluorescent) or a combination of cool white and warm white. If space is available, use two four-foot tube fixtures and a reflector.

The Best Intensity with Artificial Light

The light intensity drops off greatly two to three inches from each end of tube, no matter what kind of tube you use. With artificial light, there are no dark, gray days; instead, everyday is the fourth of July and it’s always noon. Artificial light allows you to do the following:

1. Provide strong, consistent light
2. Control the length of the day, and thus the flowering of trees by providing longer days.
3. Set up trays under the lights, thus making watering easier. This is especially true if there is a bed of stones in the bottom of the tray for excess water to drain into. The bottom of the bonsai container must be kept dry.
4. Set the tree on an upturned pot to keep it above the water. This arrangement creates a more humid area, a great benefit to trees.
5. Group trees, thus making them easier to care for.

Place trees so their tops are six to eight inches from the fluorescent tube. If the new growth is overly large or leggy, consider placing the trees closer to the tube or lengthening the hours of light. Ten to twelve hours is a good starting point that should keep your trees healthy and compact. If flowering does not occurs, increase light time by several hours. As consistency of the light is important, consider purchasing a timer to turn lights on and off.



Bonsai growing under artificial light go into dormancy, but in most cases the dormancy is unnoticeable. Remember that for trees growing under lights, every day is a sunny day. Such trees often require more water than trees on a windowsill. Watch for new growth, a sign of an active tree. If plants are actively growing, they may need fertilizer.