On indoor bonsai plants:

Tropical plants and similar “houseplants” can successfully be trained for and grown indoors year round. In milder climates, temperate plants should remain outdoors year round. In cold climates, temperate climate plants should be grown outdoors during the warm seasons of the year, but will need winter protection.  It is possible to grow temperate climate plants indoors in winter if they are first given the period of dormancy they require.

The strongest urge for beginners may be to grow their plant indoors. A few traditional species of may be grown indoors year round if they are given a dormant rest period, but you should be aware that this requires skills usually obtained from growing for a few years.

Lighting

Place your indoor plant in the sunniest window of your dwelling, but not too close to the glass or you will have problems with excessive heat buildup. This amount of light may be too intense for some tropicals that are used to growing on the forest floor, but for most woody temperate climate plants it is still insufficient. Couple this with an overhead fluorescent lamp for the woody species. Position the lamp about six inches above the plant. Twin forty watt fixtures are relatively inexpensive to purchase and use. Special bulbs are not needed.  Keep the lamp on 12 hours a day to supplement the amount of sunlight. If you lack a window with sufficient light for even low light tropicals, you can safely use fluorescent lamps as outlined above as the main source of light.

Provide a Dormant Period

The other major problem with an indoor plant is the lack of a cool dormant period. Temperate climate plants, even evergreens, need a dormant period that is activated by cooler temperatures. For most plants, this is a period of at least six to eight weeks at temperatures of 30F to 40F or lower. Most temperate woody can tolerate temperatures down to 20F without any protection. Many plants will of course, lose their leaves at this time. Other species such as Chinese Elm may or may not lose their leaves during this dormant period. At mild temperatures (above freezing) they will remain evergreen, losing all of their leaves during the following season, but not all at once, so it appears evergreen. Temperate evergreen species also need a cold dormant period, but will not lose their foliage.

Without this dormant period, deciduous species will continue to grow for as long as two years, then go dormant no matter what the season or temperature. This can be very stressful for the plant, and in some cases it is fatal.

Watering

Outdoor watering  in sunny weather is easy; the plants dry out every day, so you water them everyday. Indoors it is more difficult. You should water only when the plants need water, not to a schedule. The interval will vary with the light level, temperature, the amount of foliage, and the humidity.

There are three basic methods to determine if the plant needs water. The first is to simply pick the plant up. Dry plants are much lighter than well watered ones. You can easily tell the difference.

The second method is to scratch the soil with your finger and see how dry it is under the surface. It varies somewhat with soils and volume, but if the soil is dry down past a quarter of an inch, it probably needs watering. If the surface is still moist, it definitely does not need watering.

Fertilizing

You can fertilize to a schedule, and that is probably the best way. Most soluble fertilizers recommend that you fertilize full strength every other week. Simply water it in. Begin to fertilize when the plants start actively growing and stop at the beginning of the dormant period. For tropicals, you should continue to fertilize as long as new growth is seen.

Humidity and Air Circulation

Secondary, but important, considerations for growing indoor plants are air circulation, and humidity.

Air circulation during the summer months can be as easy as leaving the window open to get a little breeze. During the winter months you might want to get a very small fan to gently circulate some air around your plant.

Humidity is greatly over emphasized for temperate climate plants kept indoors. Many tropicals need high humidity, while temperate climate plants do not, but it is important not to let levels approach desert aridity, which can happen inside during the winter. Create some humidity for your indoor plant by placing your plant on a bed of small stones in a large flat tray filled with water. Take care not let the pot actually touch the water. The flatter the tray, the better, as this will help keep down algae and other critters because nearly all of water will evaporate each day.

It is not possible to grow every species indoors, so carefully choose only those with at least a moderate chance of success. Ficus is a really good plant for indoor growing, so you may want to try it first. Follow these tips and you should be able to grow indoor plants.

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