If you have a sunny, warm room in your house, you can grow indoor orange trees. Many different dwarf or miniature orange tree varieties are available for indoor growing, particularly cultivated varieties of calamondin or mandarin orange trees grown on dwarf rootstock. Orange trees require lots of sunlight, warmth and fertile soil, but they can easily adapt to a wide range of indoor environments. Although outdoors orange trees can grow up to 20 feet tall or more, indoor orange tree varieties often stay at just 4 to 5 feet tall.
Position your orange trees in a sunny spot, such as beside a south-facing window where the trees can receive five to six hours of full, direct sunlight each day. Don't expose the orange trees to direct, scorching sun during the hottest part of summer, however.
Keep air temperatures around your orange trees warm from spring through fall, generally between 70 to 85 degrees F. In winter, keep temperatures cooler to allow the orange trees to rest.
Water your orange trees when the top 1 inch of soil feels dry to the touch. Water the potting soil until the water drains from the bottom of the pot.
Fertilize your orange trees once each week from March through September, when the trees are actively growing. Apply a citrus tree fertilizer that contains trace elements, or micronutrients, following the directions on the label. Fertilize the orange trees once every two weeks from October through February.
Leach out any buildup of fertilizer salts from the potting soil twice each year in summer and in autumn. Pour water through the potting soil and allow it to drain through the bottom of the container, and then repeat this process two or three additional times.
Keep the relative humidity around your indoor orange trees at about 50 percent. During hot, dry weather or when the air is drier in winter, mist the orange trees daily to increase humidity levels. You may also set the orange tree's container on top of a drainage dish filled with gravel and some water.
Pinch back the growing branch tips when the new branch is 4 to 6 inches long, to induce a bushier growth form. Prune away any whole branches that are damaged or dead in February, right before new growth begins.