Some bonsai eventually must be brought indoors, if they are tender tropical plants which cannot survive winter outdoors. Also, situations may force hobbyists to keep their trees indoors year-round.

     First, make the right choices for bonsai based on your situation.

     For whatever reason bonsai must be indoors, an attempt must be made to supply an environment to which they are adapted and in which they will thrive --- or at least survive. One can create a "micro-climate" with sufficient light, humidity, and warmth for the bonsai.

     For a few smallish bonsai, a small area can be set up as below:

• The three-sided wall can be of cardboard or as decorative as you like. Its purpose is to partially enclose a volume around the bonsai to hold humidity. A light color is best, for light reflectivity. Remove the wall at night for air circulation, or if near a cold window, reverse the wall at night.
• The pebble tray is a source of moisture for the area, as well as a convenient draining spot after watering. The pots rest on the pebbles, above the water in the tray. Rinse out the pebble tray weekly to keep it fresh.
• Mist foliage frequently during the day to increase humidity, as well.
• Table placement is preferable away from heating/cooling air vents.
• The lighting arrangement is flexible; use what you can. Flourescent lights can be positions very close to the trees for maximum lighting, as they are cool.

     For those with a larger indoor collection, something like below may be necessary:

• Paving blocks are easier to deal with than gravel for cleaning, moving, etc. Area has to be cleaned (shop-vac?) occasionally.
• The plastic tray is constructed from plexiglass sheet and angled, clear "wall corner protectors", cut to length and silicone-cemented to the plexiglass bottom around the edges. All available at large hardware stores.
• Tilt the base with wood pieces toward one corner; a drain tube or fitting is silicone-cemented to a hole in the tray wall.
• Plastic sheeting stapled to and hanging from the wooden T's increase humidity. If it's cut to precise length, it can be attached on the inside of the T's and rested inside the tray, controlling splashover when watering.
• The styrofoam sheet may or may not help pots and roots stay warmer in winter. I had some, so I used it.
• Large flourescent "shop-lights" are set across the T's (or alternatively hanged from the ceiling above). The height of the T's depends on the size of one's trees. Plug lights into a "power strip", and, if desired, a timer. Additionally, a couple of incandescent light bulbs or spotlights (not shown) can be mounted to the top of the T's, but at a safe distance from foliage, for more light, and they act as little heaters during the winter.

     The next larger-sized micro-climate is called a "greenhouse".