Oranges are sub-tropical and tropical fruits. Growing orange trees in Colorado requires keeping the tree in a pot and bringing it inside for the late fall, entire winter and early spring. Orange trees should never be left outdoors when below-freezing temperatures are possible. Although it can grow from seed, an orange tree can take up to seven years to produce fruit. Growing a potted orange tree in Colorado from nursery stock will result in faster, sweeter oranges.
Begin working with your nursery tree in its small container. Transplant the tree every spring into a larger pot until it is in a container about the size of a whiskey barrel.
Keep the orange tree in a south-facing window during the winter or other cold-weather periods. Move the tree and container to a location where it will get sun all day in mid-spring.
Water the orange tree frequently. Soak it as soon as the top 1/4-inch of soil feels dry.
Mist the tree every morning and keep it in a large pan filled with gravel and water to create a humid space around the orange tree.
Fertilize the tree regularly with a balanced fertilizer. Follow the package's fertilization instructions for flowering plants.
Move the potted orange tree indoors in temperatures of less than 45 degrees F.