Citrus trees (Citrus spp.) need warmth, and they can be grown successfully year-round in gardens only in the warmest parts of the southern United States. With protection from cold, however, small citrus trees can be grown elsewhere, even in Tennessee.
In general, citrus trees are too sensitive to cold to be able to survive winters outdoors in Tennessee, where the climate ranges from U.S. Department of Agriculture plant hardiness zone 5b through 8a. Even the most cold-tolerant varieties are likely to struggle in the mildest areas of the state.
A better option for Tennessee gardeners who want to grow citrus is to plant dwarf trees in containers that can be taken indoors when the weather begins to turn cool. Meyer lemon (Citrus x meyeri) is one small cultivar that does well in a pot; although it is hardy in USDA zones 9 through 11, it can thrive in Tennessee when given the proper care.
Pots and Soil
Choose a large container for each citrus tree. Usually, a pot about 12 inches in diameter is suitable for a 2- to 3-year-old citrus tree. Ensure each pot has bottom drainage holes. Use a commercial potting mix that will retain moisture but drain well and thoroughly. Plant each tree in the center of its container, placing it at the same soil depth at which it grew in its nursery container.
When choosing a site in your garden or on your deck or patio for container citrus trees, look for a location that gets direct sun exposure for as much of the day as possible, preferably at least eight hours per day. A sheltered location near a south-facing wall can help to protect the trees from low temperatures and wind, as long as the wall doesn't cast shade on the trees for long periods of time.
Fertilizer and Irrigation
Fertilize container-grown citrus trees with a slow-release, granular, garden fertilizer, sprinkling it on the soil around the base of each tree -- but not touching its trunk -- in early spring just as the trees' new leaf buds are opening. Water the soil after the fertilizer application. The amount of fertilizer to use depends on the fertilizer's nitrogen content and the age of the tree. A 2-year-old citrus tree in a container, for example, needs 1/10 pound of nitrogen per year, but a 5-year-old container tree needs 1/2 pound of nitrogen. A fertilizer with a 30-10-10 nutrient proportion contains 3 pounds of nitrogen in every 10 pounds of fertilizer.
Be careful not to overwater container-grown citrus trees. Wait until the top 1 inch of their soil is dry to the touch, and then water until the water runs out through the pots' drainage holes; do not allow the pots to sit in drained water. Reduce watering frequency in winter when the trees' growth slows.
Move the potted trees indoors in fall. Many citrus species can tolerate short periods of temperatures slightly below freezing, 32 degrees Fahrenheit, but it's a good idea to be prepared to move the trees indoors before the first frost. Choose an indoor location near a window that is exposed to direct sunlight for at least six hours per day. Make the move gradually, taking the plants indoors at night over the course of one month before the first frost.
Move the trees outdoors in spring after the danger of frost has passed. As with the move indoors, make this move outdoors gradually, taking the trees outdoor during the day and bringing them back indoors at night for the first month.