How to Care for Indoor Bonsai Plants

Growing miniature, sculpted trees -- the art and practice of bonsai -- can be traced to the 1300s in China. Today, bonsai plants add a touch of nature and an element of sculptural aesthetics to any home's decor. For years of enjoyment from your indoor bonsai trees, provide them with everything they need to be lush and healthy.

Indoor bonsai trees are kept in potting soil in small containers and dry out very quickly because all sides of the plants are exposed to air movement and heat. The frequency that each tree needs watering depends on the size of its pot and where it's set up. In fact, some gardeners need to water their bonsai trees twice each day or more often.

In general, always let the top surface of a bonsai tree's potting soil dry out before watering. Then irrigate the pot's soil until water drips out of the container's bottom drainage holes. Each bonsai's pot must have bottom drainage holes.

If you have bonsai trees' pots set on trays to collect excess water, then empty the trays as needed. Don't let a tree's pot sit in a tray of water for longer than one day.

Due to their container settings, bonsai trees quickly deplete the nutrients in their pots. Fertilize your bonsai trees once each month during the trees' active spring and summer growing season.

Use any houseplant fertilizer, but dilute the label's recommended amount to 1/4 or 1/2 strength. If, for example, you use a granular 10-10-10 fertilizer formulated for small houseplants and its label recommends using 1/2 teaspoon of that fertilizer per plant pot, then use 1/8 or 1/4 teaspoon of the fertilizer per pot instead. Sprinkle the granular fertilizer on the soil surface around the base of each bonsai tree, but don't let the fertilizer touch the plant. Water the soil to dissolve the fertilizer, using enough water so that moisture drips out of the pot's bottom drainage holes.

Over the centuries, multiple styles of bonsai trees have evolved. The simplest, easiest option is to allow each tree to grow upright, pinching off its branches as necessary to create a symmetrical, natural-looking shape. For inspiration, observe a mature version of the tree species to see the shape the tree naturally takes in the wild.

If you have a specific shape that you'd like to train a bonsai tree to grow into, then wrap one of its young, flexible branches in copper wire, and bend the wire in the direction you want the branch to grow. Over the course of a couple months, the branch will take on this growth direction and maintain the growth pattern after you've taken off the copper wire.

Bonsai trees need little pruning other than occasionally pinching off their new growth that is outside of the shapes and forms that you want for the plants. If you notice a branch or leaf growing in a wrong direction, simply pinch it off with your thumb or forefinger.

You can wrap bonsai trees in copper wire to train their growth any time of the year. If, however, you grow deciduous trees, which lose their leaves for winter, then the winter season may be the easiest time to train the trees because leafless branches are easier to handle than leafy branches.

Forest trees raised as compact bonsai plants do best when grown outdoors, but they can be taken indoors for viewing. When brought indoors, these bonsai trees should be kept in a very well-ventilated area and kept indoors for no longer than three hours. Example forest trees traditionally used in bonsai include:

Willow oak (Quercus phellos), which is hardy outdoors all year in U.S. Department of Agriculture plant hardiness zones 5 through 9.

Japanese maple (Acer palmatum, USDA zones 5 through 8). This tree can become invasive when grown in the ground outdoors. Growing it in a pot prevents that problem. 

English hawthorn (Crataegus laevigata, USDA zones 4 through 7).

If you hope to keep bonsai trees indoors most of the time, then use woody tropical or subtropical varieties, which do better as bonsai than traditional forest trees. Options include:

Common camellia (Camellia japonica, USDA zones 7 through 9).

Ming aralia (Polyscias fruticosa, USDA zones 11 through 12).

Singapore holly (Malpighia coccigera, USDA zones 11 through 12).

Regardless of the type of bonsai trees you grow, the symmetrical plants will look their best when set against a very plain, simple and non-cluttered background. For example, an indoor bonsai tree looks best when placed against a blank wall while an outdoor bonsai looks best when placed on a neutral-colored gravel bed.

When choosing a location for your bonsai trees, keep in mind that most bonsai need full-sun exposure. That's at least six hours of direct sunlight daily.