Grow an indoor lemon tree like any other indoor plant that needs as much sun and humidity as you can give it. Indoor lemon trees will even produce lemons for you, particularly if you give it a little assistance by pollinating the blossoms.
Choose a clay or ceramic container that is large enough to support the tree. A lemon tree growing in a pot indoors needs a pot that is at least 16 inches in diameter. Make sure there are adequate drainage holes in the bottom.
Use regular indoor potting soil. Mix 4 parts indoor potting soil, 1 part perlite and 1 part regular garden compost. Use this mix to pot up and grow your lemon tree.
Place your lemon tree in a south-facing window or under grow lights. They will also grow adequately in a west-facing window, but south-facing is preferred. They need as much sun indoors as you can give them.
Water regularly. Lemon trees growing indoors need to be watered regularly to compensate for dry indoor air. When the surface of the soil feels dry, water until it drains out of the bottom of the pot. Do not allow the soil to dry out completely as this will be fatal to the tree.
Provide your indoor lemon tree with extra humidity. Fill its drainage saucer with small pebbles. Excess water that drains out when you water it will collect in the saucer and the rocks will keep the bottom of the pot from sitting in water. If the water level rises above the level of the rocks, remove the excess. You can also run a humidifier in the room where it is growing. Grouping a number of other indoor plants in the room near your lemon tree will also increase the humidity of the room.
Fertilize regularly. Feed your indoor lemon tree monthly with either a fertilizer specially formulated for indoor citrus trees or with a general all purpose fertilizer. Follow the manufacturer's instructions as to the correct amounts of fertilizer to apply.
Move your lemon tree outdoors during the summer months. Place it in the shade for 7 to 10 days before moving it into full sunlight. It needs this adjustment so the leaves do not become sunburned from the intense rays of the sun. Indoor winter sun is not as powerful as outdoor summer sun.
Inspect regularly for insects. Look in the crooks of the branches and the undersides of leaves for a white powdery looking substance. This is most likely the web of spider mites, the most common pest of lemon trees. Spray with horticultural oil to smother the mites, following the manufacturer's instructions. Be sure to spray the undersides of the leaves, the trunk and the soil.