Most lemons (Citrus spp.) are not hardy in North Carolina, but that doesn't mean you can't still enjoy these beautiful trees. The sunny climate of North Carolina, which covers U.S. Department of Agriculture plant hardiness zones 5b through 8b, is good for lemons grown in outdoor containers. Moving the containers indoors during the winter will protect the tender trees from cold damage. In the southern parts of the state, certain lemons can also be grown in-ground.
The only variety of lemon for growing outdoors year-round in parts of North Carolina is the Meyer lemon (Citrus x meyeri "Improved"). It is most likely a cross between a lemon and an orange (Citrus sinensis) or tangerine (Citrus reticulata ), and the fruits are less acidic than true lemons. Oranges and tangerines are hardy in USDA zones 9 through 10.
Meyer lemon is reliably hardy in USDA zones 9 through 10, but the tree can be grown in zone 8 with protection. This means that with proper care, you can grow Meyer lemons in-ground in the southern and coastal regions of North Carolina. In cooler locations, they can be grown in containers just like other lemons. Meyer lemons are compact trees that grow to about 10 feet tall, so space plants 8 feet apart in the garden.
For lemons grown in-ground, choose a sunny location on the south or southeast side of a building. As long as the soil is well-drained, Meyer lemons adapt well to most soil conditions except heavy clay. Water every few days after planting a new lemon tree, then gradually reduce watering to every seven to 10 days for the next couple months. Mature lemons require water every two to three weeks to keep the soil moist but not soggy. If there hasn't been rain for a few weeks, such as in the dry autumn months, water lemon trees deeply.
Use a slow-release citrus fertilizer that contains trace nutrients like magnesium and iron as well as the usual nitrogen, phosphorous and potassium. Apply citrus fertilizer two to three times a year starting in the spring, following label directions for the size of your tree. When using a fertilizer with an N-P-K ratio of 13-7-13, a tree 2 to 3 feet tall needs a total of 3/4 pounds of fertilizer each year spread out over three applications, while a tree 6 to 8 feet tall needs 2 1/2 pounds of fertilizer divided into two applications.
True lemons (Citrus limon) are the citrus species most sensitive to cold. They are hardy in USDA zones 9 through 11 and require frost protection even in these zones. In North Carolina, they can only be grown as container plants, which are moved to a frost-free location during the winter months.
When growing lemons in containers, commercial potting mixes work well as long as they are well-drained. If you want to mix your own potting soil, combine 1 part each clean sand, peat and pinebark. Water container-grown lemons when the top 1 to 2 inches of soil is dry to the touch.
Start lemon trees in containers 15 inches wide and 15 inches deep with drainage holes. When the lemon trees start to outgrow their containers, you can either move the tree to pot 25 percent larger than the old container or lift the tree and prune off about one-quarter of the root mass. Repot trimmed trees with new potting soil, then prune off about one-third of the foliage. Disinfect pruning tools by soaking them for five minutes in a mixture of 1 part bleach to 3 parts water. Rinse with clean water and allow to dry before use.
Like other citrus, lemons grown in containers need a fertilizer that contains micronutrients like iron, zinc, manganese, boron and copper. Follow instructions on the fertilizer packaging for potted citrus trees. For a dry fertilizer with an N-P-K ratio of 6-4-6, apply 2 tablespoons for a 15-inch pot or 2 1/2 tablespoons for an 18-inch pot. Sprinkle fertilizer evenly over the potting soil three times a year. Make the first application when new growth begins, and the next two applications at 90-day intervals.
If a light frost is expected, bring container plants into a sheltered location and cover in-ground plants with a blanket or burlap. Another trick for protecting in-ground Meyer lemons is to string Christmas lights through the branches before covering the tree. The heat from the light bulbs will help keep the leaves and branches from freezing. Without this type of protection, Meyer lemons suffer damage in temperatures that fall below 20 degrees Fahrenheit.
In the late fall, plan to move container plants indoors gradually. Drastic changes in light levels stress the trees. About three weeks before you expect the first frost in your area, start moving the tree to shadier and shadier locations to acclimate it to lower winter light-levels indoors. Make sure you move container plants indoors before true lemons are damaged by temperatures dipping below 25 degrees Fahrenheit.