Mandarin orange trees are ideal for container growing. The plant is small enough for a large container and can be grown outdoors in the summer and taken inside during winter months in colder climates. Though mandarins are cold hardy to approximately 20 degrees Fahrenheit, according to the Alabama Cooperative Extension website, container grown trees are more susceptible to the cold because the roots are exposed and chill much faster. Mandarins need a sunny spot and grow best outdoors on the patio, but can be grown indoors with adequate light.
Choose a large container. Plastic pots are lighter, which is nice if you are moving the tree, but may be unstable in windy weather. Clay is often a better choice, especially if a wheeled dolly is available for moving the plant.
Prepare a light potting mix with plenty of organic matter. Add perlite or pumice to help aerate the soil.
Plant the tree so that it is slightly higher than it was in the nursery container. The bud union must remain above the soil level.
Water the tree regularly. Keep the soil moist but not soggy.
Turn the tree every few days when indoors or if sunlight is not evenly available. Trees that receive sun from only one direction will lean toward the sun as they grow.
Withhold fertilizer after planting until new growth appears, then with a slow-release fertilizer or a citrus formula high in nitrogen. Continue fertilizing four times a year or as recommended on your specific fertilizer. (reference 2)
Move mandarin orange trees indoors before the first freeze. Bring the tree inside for several hours, gradually increasing the time indoors until the tree is fully acclimated to the indoor climate. Reverse the process in the spring, bringing the tree outdoors slowly over the course of two weeks. In warm climates, bring the tree indoors only when a freeze is expected.
Check the tree annually for signs of pot bound roots. Move the tree to a larger container when the roots begin to outgrow the container.