As long as you have windows in your house that receive full sun, you can grow orange trees with no trouble indoors. The key lies in choosing dwarf orange varieties, since these have been bred to grow only to about 6 feet in height, much smaller than standard orange trees. Both spiny and spineless varieties are available. With well-drained soil, full sun daily and appropriate care, your orange trees will grow well inside your house.
Choose among a variety of dwarf orange trees. Buy from a local nursery or online from a reputable grower. Some dwarf orange trees include: Calamondin, sweet orange, and Otaheite (a cross between a mandarin orange and a lemon).
Plant the young tree in a well-drained all-purpose potting soil mixture with lots of organic matter in it. Orange trees, like all citrus, like a slightly acidic soil. Ample organic matter in the soil, such as peat moss, ensures acidity. Choose a pot that is twice as big as the root ball.
Stick a moisture meter in the soil with each tree. Orange trees are not very picky plants, but they don't like too little or too much water. A moisture meter is an easy way to make sure you only give your orange trees the water they need.
Fertilize on a regular basis with a citrus-specific fertilizer. The nitrogen-phosphorus-potassium (NPK) level should be about 20-20-20. During the growing season, fertilize once every two weeks. Follow the manufacturer's instructions for proper application.
Mist orange tree foliage daily, especially during the dry months of winter. A humidifier can also be helpful in the winter. Orange trees prefer a humid climate.
Hand-pollinate the flowers when they bloom in order to ensure good crops. Rub a small round paintbrush across the top of the stamens (the long stalks in the middles of the flowers) to collect pollen. Then rub the brush inside the pistil (the base of the flower). Birds and bees would do this if the tree was planted outside. Since you are growing your oranges inside, you will have to be both birds and bees if you want oranges. How soon you can expect flowers and oranges on your trees varies by species.
Repot your orange trees whenever they become rootbound, approximately every two years. If you notice that a tree seems unhealthy, no matter how well you have been taking care of it, check the roots. If there is no more room in the pot for them to grow, it is time for a larger pot. Simply use potting soil in a larger pot and carefully move the tree from the smaller pot to the larger one. Make sure to cover all the roots with soil.