The miniature orange tree, Citrofortunella microcarpa, is the most cold-tolerant of the subtropical mandarin group of citrus plants. While it can endure short bouts of temperatures as low as 25 degrees F, the calamondin does have its limits and will die if subjected to frost. The good news for cold-climate gardeners is that the miniature orange can thrive well as an indoor container specimen. Its small, manageable size of around 3 feet and relatively low maintenance requirements make it a good choice for enthusiasts with limited growing space. The miniature orange tree typically sets bright orange fruits during the winter, so treat yourself to a welcome splash of lively indoor color during the dreary months.
Place the miniature orange tree in the brightest spot of your home. This sun worshiper requires at least four hours of exposure daily to bloom and set fruit. If it's not possible to provide sunlight, set the plant in the brightest light available. The happy miniature orange tree can be expected to bloom and fruit about twice annually with adequate light.
Provide your calamondin with a warm spot. It will perform satisfactorily with temperatures above 55 degrees F, but thrives best in a 70- to 80-degree environment.
Poke a finger into the top 1 inch of the newly acquired miniature orange tree's potting medium. If it feels dry, set the plant in the sink and soak it slowly until you see water running from the holes in the pot. Allow it to drain for a couple of hours. Let the top one-fourth of the soil dry out before watering just enough to evenly moisten the soil surface during the winter. Increase frequency throughout the growing season to evenly moisten the soil surface when the top 1 inch dries out.
Scatter some pebbles or gravel in the bottom of a drip tray. Set the plant on the pebbles. Check the drip tray 24 hours later and empty the excess water. Keep enough water in the tray to cover the pebbles about halfway to provide the plant with humidity, but don't allow the pot to rest in the water.
Feed the miniature orange tree a good all-purpose citrus or high-acid fertilizer. Follow the packaging instructions carefully. Fertilize once every two months during the winter, and monthly throughout the growing season.
Use a moistened soft cloth or sponge to wipe dust from the tree's leaves. This will go a long way in preventing scale infections.
Prune the calamondin in early spring before buds are set, if necessary. Remove any dead, damaged or diseased stems with clean, sharp shears. Make your cuts all the way back to the point where the stem grows from a larger branch, and don't leave any stubs. Prune some of the interior stems out if foliage becomes very thick. This will open it up to circulate more light and air throughout all areas of the crown. Your miniature orange tree will maintain an attractive habit on its own, so no further shaping is needed.
Set the calamondin outside in bright sunshine when sustained temperatures remain above 55 degrees F. Do this gradually, beginning with morning sun exposure only for the first several days. Increase the plant's sunny time over a couple of weeks to acclimate the plant to all-day exposure. Bring it back indoors for the winter when temperatures begin dipping below 50 degrees F, no matter how briefly. The temperature drop would cause the plant to enter winter dormancy.