Louis XIV of 17th century France grew 3,000 orange trees in a greenhouse called an orangerie, and so have others who crave a glass of fresh juice in climates that are too cold for citrus to grow outdoors. If you select a dwarf variety of orange, lemon, lime or tangerine, it will fit nicely into even a small greenhouse. Growing your citrus in a large pot is helpful, because all types of citrus trees love the natural sunlight and will benefit if you move them outdoors, as Louis did, in the summer months.
Plant your citrus tree in a large pot with at least one drainage hole, using a standard potting soil mix. Make sure to leave the root collar above the soil line and the root crown just below. Move it into your greenhouse in fall, before your first frost.
Provide sufficient light for your citrus tree: if your greenhouse does not receive at least eight hours of sun, hang a grow light or a fluorescent shop light above your tree.
Maintain a temperature between 55 and 95 degrees Fahrenheit.
Water your tree when the soil becomes slightly dry.
Fertilize your citrus tree with a plant food designed for citrus or one having an N-P-K ratio of 3-1-1 because they need a good amount of nitrogen. Repeat your fertilizer application every two months during the tree's active growing season (spring through late summer). Don't fertilize during winter.
Prune suckers and water sprouts from the base of your citrus tree when you see them starting to form. You can also prune your citrus tree to keep it a manageable size for your greenhouse.