In-Ground Citrus Production

Citrus has been grown in South Carolina for hundreds of years.
Zack Snipes, ©2020, Clemson Extension

Citrus species have been grown in South Carolina for hundreds of years in the coastal plains and sea islands. Cold winter temperatures are the main limiting factors for growing citrus in South Carolina. Most winters along the coast are mild enough, allowing citrus to thrive. However, it only takes a few hours below a specific temperature to severely damage or kill citrus. Researchers at Clemson University have been evaluating citrus species for cold tolerance in recent years.

“Kishu Mandarin in Beaufort County, SC”
Zack Snipes, ©2022, Clemson Extension

Purchasing Citrus

When purchasing young citrus trees, it is essential to note that trees must mature before flowering. Young, grafted oranges, grapefruits, and mandarins must grow for 5 years before they will flower and produce fruit. Lemons require 1 to 3 years to overcome juvenility. Therefore, purchasing larger specimens will often lead to faster fruit production. While more expensive than younger trees, older trees typically have better cold tolerance, thus improving the chances of survival in a cold snap.

Whether grown from seed, cuttings, or purchased- citrus plants cannot be taken outside of Charleston, Beaufort, or Colleton counties in South Carolina due to the Citrus Greening Quarantine. Although not recommended, plants can be moved from other counties in South Carolina if they have not been in or originated in Charleston, Beaufort, or Colleton Counties.

Culture

Keep the root flare at soil level by digging the planting hole at exactly the same depth as the root ball and 2 to 3 times wider.
Barbara H. Smith, ©2018, Clemson Extension

Site Selection: Citrus trees should be planted in a full-sun location to achieve maximum production. Citrus prefers well-drained soil with a pH in the 6.0 to 6.5 range. When planting trees, make sure to plant the tree with the upper-most roots at, or even above, soil level. Often, trees are planted too deep, and soil or mulch will touch the tree trunk, leading to poor tree health over time. Trees near structures such as houses and brick walls may benefit when temperatures plummet during cold snaps. Southern-facing structures will provide more heat sinks than structures facing different directions. Trees may also benefit from being planted near water, such as lakes or ponds. Bodies of water hold heat better than air and can create a warmer microclimate than the surrounding area. Most cold weather that injures or kills citrus will come from the north or west, so structures or trees blocking a northern wind could help protect trees enough to survive a cold event. It is also important to avoid low spots (frost pockets) as cold air sinks to the lowest point during a frost event. For more information on growing citrus in containers, see HGIC 1363, Growing Citrus in Containers.

Irrigation & Fertility: Citrus trees need a consistent water supply for proper growth and production. Trees should be watered multiple times per week during the establishment phase. Incorporating organic matter when planting and using mulches around the base of the tree can help with water retention, thus potentially reducing the number of times water is needed. During hot, dry periods, trees will need to be watered more frequently. Before irrigating, check the top 2 to 3 inches of the soil to see if there is any moisture. The root ball should never completely dry out, nor should it be overly saturated for extended periods of time.

A soil sample is recommended before planting so that corrections can be implemented in advance to make fertilizer or liming decisions and avoid nutritional deficiencies. Once trees are planted, a leaf tissue analysis during the summer months (4- to 6-month-old spring flush leaves) can provide recommendations for nutritional needs for the following season. Often, micronutrients are lacking and are very easily noticed in leaf tissue. Micronutrient deficiencies are easily corrected. The Clemson University Agricultural Service Laboratory can test soil and leaf tissue samples. For more information, please visit the Agricultural Services Laboratory.

Fertilizing after July is not advised as plants will be too succulent going into the winter months, causing them to be more susceptible to winter damage or death.

Table 1. Fertility Recommendations for In-Ground Citrus

Adapted from Rouse, Robert & Zekri, Mongi. University of Florida. Citrus Culture in the Home Landscape. February 5, 2015. https://edis.ifas.ufl.edu/publication/HS132

Pollination: Most Citrus species are self-pollinating. Tangerines are the exception as they require cross-pollination; therefore, it will be necessary to have two or more varieties for proper pollination. Their fragrant flowers attract pollinators, such as honeybees and bumble bees. Typically, citrus flowers in mid to late spring.

Problems: The most concerning disease of citrus is Citrus Greening disease. The Asian citrus psyllid, an insect the size of a gnat, spreads this devastating bacterial disease when feeding on newly developed leaves and flushes. The psyllid was found in Charleston County in 2008. As a result, there is now a ban on citrus being moved or shipped from Charleston, Beaufort, or Colleton Counties. Please see the Clemson Regulatory Services site for more information on the quarantine of this disease.

In poorly drained soils, root rots, such as Pythium or Phytophthora, may lead to poor tree health and eventual death. Other diseases, such as citrus canker, Alternaria brown spot, citrus scab, and greasy spot, can be of significant concern and should be monitored. Sooty mold is a non-parasitic organism that grows on the honeydew of aphids, whiteflies, and soft-scale insects. Sooty mold can cover green plant tissue and inhibit photosynthesis. Proper management and prevention of these pests can minimize the prevalence of this problem.

For information on Citrus Insect Pests, please see HGIC 2221, Citrus Insects & Related Pests.

Recommended Varieties for South Carolina

Commercially available citrus are grafted, meaning they have the rootstock of one species and the scion or top of another species. Most rootstocks are chosen for their cold hardiness, vigor, and disease resistance. There are many rootstocks available for nurseries to use. However, many times, the buyer has fewer options when purchasing grafted trees. Some standard rootstocks include Carrizo, Roubidoux, US-942, sour orange, and Swingle. Rootstock selection can have an impact on the cold hardiness of citrus scions.

The recommended varieties were tested at Clemson’s Coastal Research and Education Center in Charleston, SC. This is not an exhaustive list of all cold-hardy citrus.

A selection of citrus harvested in Charleston, SC in 2022.
Zack Snipes, ©2022, Clemson Extension

Kumquat varieties (Citrus japonica) are extremely cold-hardy and performed best in lab studies. Calamondin (citrus x macrocarpa) is another species of citrus that does well in South Carolina and has survived in research trials.

Satsuma (Citrus unshiu) and Mandarin (Citrus reticulata) citrus generally have more cold tolerance than most other citrus. Satsuma varieties, such as Owari, Brown’s Select, Tango, and Gold Nugget, have performed well in lab and in-field studies. These varieties endured temperatures of 16.5 °F during the Christmas freeze of 2022. Mandarin varieties, such as Miho, Ponkan, Shiranui, Sugar Belle, Keraji, Kishu, Ugli, and Xie Shan have performed well in the field.

Ichang lemon (Citrus ichangensis) is extremely cold-hardy, but, it has a very unpleasant taste. Many species are bred with Ichang for its cold tolerance. Meyer lemon (Citrus x meyeri) is the most cold-hardy lemon variety that has palatable fruit. Once established, Meyer can be fairly cold-hardy, but juvenile trees are susceptible to cold events. The 16.5 °F event in Christmas 2022 killed all Meyer trees in the experiment.

Established grapefruit trees (Citrus X paradisi) are common on the sea islands of South Carolina and can produce abundant yields of five hundred fruit or more per tree. However, neither Marsh Pink nor Flame varieties survived the 16.5 °F cold event in research trials.

Cara Cara (Citrus sinensis ‘Cara Cara’) and Dream (Citrus x aurantium ‘Dream’) are two species of oranges that have fared well in research trials, but more time and data need to be collected to see how they will do over time.

Managing Cold Events

Young mandarin-type citrus is relatively unphased by 16.5 F temperatures.
Zack Snipes, ©2023, Clemson Extension

Managing cold events is both a function of temperature and time. Trees have a minimum temperature that they can withstand and survive. The duration of that temperature is what ultimately injures or kills trees. Trees become cold-hardy as they mature. Trees develop cold hardiness during the season as well. For example, chilly nights, weeks or days before a frost, may increase cold hardiness. Also, trees exposed to a cold event in February (after many chilly nights during winter) are more cold-hardy than those exposed to the same event in November, without previous cold acclimation.

Protecting the graft union is the key to keeping trees alive during cold events. If the graft union survives a cold event, the entire scion can die and appear lifeless, but the tree is still alive at the union and can regrow.

Soil banking is a technique that can be used to protect the graft union during the winter. In November, soil is mounded up around the tree covering the graft union. The soil serves as a bank for heat during the cold months. The soil can be carefully removed in March of the following year.

Some citrus growers will opt to cover their citrus during cold events. Often, burlap, blankets, pipe insulation, or even pool noodles can cover the graft union. Covering young trees with blankets can conserve enough heat to keep trees alive. Weed management is critical during cold events as bare soil can radiate heat up into the canopy of the tree. Soaking the soil via irrigation a few days before a cold event can also help bank heat in the soil.

Citrus leaves will turn brown and sometimes fall off after a cold event. It may be tempting to cut the tree down, as damaged trees can be unsightly, but resist that urge and wait until late summer. Rootstocks used are extremely cold-hardy and can survive cold events, allowing the entire plant to survive. It is common to see new growth in August from the scion after a previous winter’s cold event.

References:

1. Rouse, Robert & Zekri, Mongi. University of Florida. Citrus Culture in the Home Landscape. February 5, 2015. https://edis.ifas.ufl.edu/publication/HS132
2. Zekri, Mongi & Rouse, Robert. University of Florida. Citrus Problems in the Home Landscape. September 19, 2019. https://edis.ifas.ufl.edu/publication/HS141

The authors thank SC Department of Agriculture for providing funding for this project (Evaluating and Promoting Cold-Hardy Citrus Species for South Carolina; AM200100XXXXG073).

Originally published 05/24