Citrus

History

Citrus are members of the Rutaceae family, also known as the rue family, which includes mostly flowering woody trees and shrubs. Trees in this family produce citrus fruits, including popular crops for Louisiana such as satsumas, oranges, and kumquats (see Figure 1). Citrus trees cannot survive in areas that regularly freeze, so production is concentrated along the Gulf Coast, particularly in southern areas of Louisiana and Florida.

Sweet oranges are tropical and subtropical trees likely native to Asia (northeastern India and southern China); they were transported throughout the Mediterranean by Italians and Portuguese from 1450-1500 (see Figure 2). Spanish explorers brought the orange tree to South America and Mexico in the 1500s and then to Florida in 1565 and probably to New Orleans as well. In the 1700s citrus migrated westward to Arizona and California.

Grapefruit is considered a pomelo mutation and is likely native to the West Indies (see Figure 2). It was first recorded in 1750 in Barbados and then in 1814 the name “grapefruit” was coined in Jamaica. Grapefruit trees were transported to Florida in the early 1800s.

Satsumas are likely native to China but were first recorded in Japan more than 700 years ago (see Figure 2). Japan is still the largest producer of satsumas. These citrus trees were not reported in the U.S. until the late 1800s in Florida. Many satsuma trees were imported from Japan in the early 1900s and planted throughout the Gulf Coast.

Lemons are likely native to Asia, appearing in records from 200 A.D. in Italy and from 700 A.D. in Iraq and Egypt (see Figure 2). Lemons were then distributed throughout the Mediterranean region and brought to Hispaniola (modern-day Haiti and Dominican Republic) by Columbus in 1493. These Spanish explorers brought lemons to Florida along with other citrus, and expansion reached California by the mid-1700s.

Citrus trees are perennials and can be generally characterized as either sweet or acidic. Trees that produce sweet citrus include satsumas, oranges, mandarins, tangerines, tangelos, and grapefruit. Acid types of citrus include kumquats, calamondins, lemons, and limes.

Varieties

There are many varieties of citrus trees that vary by fruit size and taste, harvest time, and cold hardiness (see Figure 3). Citrus can be produced in Louisiana and trees are generally easy to grow, though optimal growing area is limited due to potential freezes.

It is important to select citrus types that are suitable to grow in the South, Central, or North region (see the three zones in Figure 4), based on risk of hard freezes. In Zone A (South Louisiana), all citrus varieties can be grown since there is very low risk of hard freezes. Zone B (Central Louisiana) has moderate risk for hard freezes. In this area, cold-hardy types like kumquats and satsumas should be selected, while moderately hardy types like sweet and navel oranges, mandarins, and grapefruits may be planted if protected in freezing weather. Zone C (North Louisiana, or the top half of the state) has regular potential for hard freezes and only cold-hardy types (kumquats and satsumas) should be planted and protected during hard freezes.

Kumquats are one of the most cold-hardy citrus types, tolerating temperatures as low as 15-17 degrees F. Kumquats are small, sweet or acidic, orange, seeded fruits about 1 inch in diameter (see Figure 5) that can be eaten fresh (consumed with the smooth rind) or used in making candies, marmalade, or jellies. These vigorous, attractive, shrub-like trees generally ripen from mid-October to February.

Satsumas are very popular and grow successfully in South Louisiana. Trees produce easy-to-peel fruit ranging in size from small to large (by variety) and maturing throughout the fall. Satsumas tolerate colder temperatures, require less cold protection, and produce a more consistent crop than other types of sweet citrus. Satsuma fruits turn from green to yellow as they ripen and finally to orange at full maturity (see Figure 5). They can be consumed starting when fruits turn yellow, extending the harvest season. Satsumas are within the citrus group called Mandarins, which also include mandarins, tangerines, and tangerine hybrids.

Sweet and navel oranges are moderately cold hardy and are also very popular in South Louisiana, although hard freezes (20 degrees F and lower) can severely damage trees. Some varieties may be planted in the Central region if protected from the cold. Sweet orange trees produce round, sweet, and flavorful orange fruits with varieties that vary from seedless to those having many seeds (see Figure 5). Sweet oranges ripen from October to June, depending on variety. Navel oranges have a navel-like secondary fruit formed within the end of the fruit and are generally larger than other sweet orange varieties.

Grapefruit is also moderately cold hardy and may be grown successfully in South Louisiana and in the Central region with cold protection. Grapefruit trees produce medium to large, round fruit with a tart flavor and few seeds. The skin can be yellow to orange in color, with yellow, pink, or red flesh (see Figure 5). Generally, grapefruit is ready to harvest from November to May, depending on the variety.

Other citrus like mandarin, tangerine, tangelo, and calamondin are only recommended for South Louisiana, as they are fairly tender. Mandarin trees produce medium to large fruit with a deep orange skin and honey flavor. Tangerine trees produce medium to large, slightly flattened fruit with an orange-red, flavorful flesh. Tangelo is a hybrid between grapefruit and tangerine, producing medium-sized, deep orange fruit that is very juicy and flavorful. Fruits for these citrus varieties generally mature from November to February. Calamondin is a small, round fruit that looks similar to a tangerine with very acid pulp and a high pectin content (great for marmalade). Fruits are yellow to orange and are used as a substitute for limes and lemons. Calamondin has good cold hardiness and is attractive as an indoor or container plant. See Figure 5.

Lemons and limes are the most tender citrus varieties, with only a few varieties recommended for South Louisiana, and then only in containers or in protected areas and protected from freezing temperatures. The Meyer lemon, a cross between a pomelo and a mandarin, is the most cold hardy of the lemon/lime group, surviving to mid-20 degrees F. Producing tart yellow (lemon) or green (lime) fruit, these trees set fruit starting in October and often continue to produce throughout the year. See Figure 5.

See the recommended citrus varieties for Louisiana in Table 1.

Table 1. Recommended Citrus Varieties for Louisiana

When and How to Plant

It is recommended to start with a young, containerized citrus tree, which are available year-round. Trees are usually grafted and it is important to obtain healthy plants from a reputable nursery and look for a certificate indicating that the tree has been inspected and is free of disease. It is recommended to select a 2- to 4-foot-tall tree with 3 to 4 evenly distributed, well-developed upward-growing branches.

Transplanting can be done at any time of the year, although late winter to early spring, after danger of freezing temperatures, is ideal. Refer to the Citrus Planting Guide (Table 2) for the recommended months to plant young trees, along with details on spacing. Different types of citrus have different recommended spacings based on the size of the tree at maturity.

It is recommended to remove about an inch of growing medium around the root ball before transplanting for better establishment and growth. The outer roots will be exposed, which will allow them to grow quickly into the soil. At the recommended spacing, dig a hole that is deep enough so the citrus trees can be set at the same depth as they were in the pot. The hole should be twice as wide as the root ball. Fill in the hole around the plant with the native soil dug from the hole, firm the soil around the plant, and water thoroughly (see Figure 6).

After transplanting, it is recommended to remove any grass or weed cover extending out about 3-5 feet. Cover with a thick layer (3-6 inches) of organic mulch and prune some of the low, small branches up to 18 inches from the soil level.

Table 2. CITRUS PLANTING GUIDE

Where to Plant

Citrus trees are most productive when grown in full sun (6 hours/day) but some types will tolerate partial shade. Citrus trees do best in a well-drained sandy loam soil with a pH between 6.0 and 8.0. Citrus doesn’t tolerate excessive moisture but will grow in many soil types if well-draining or if planted in raised beds. Citrus trees prefer soil high in organic matter.

It is recommended to plant trees at least 6-8 feet away from any structures or pavement, depending on the mature tree size for the particular citrus type. Avoid planting near drain fields or septic systems. It is recommended to plant citrus trees in a protected area such as near the south side of a building, especially in Central and North Louisiana. This will aid in cold weather protection from the north.

Citrus trees are self-pollinating, as flowers have both male and female parts. Some tangerine and tangelo varieties, however, will have better fruit set when cross-pollinated with another variety of tangerine, tangelo, or orange tree. Most citrus trees flower during the spring and summer to produce fruit in the fall and winter, depending on the citrus type. Trees usually start bearing fruit in the fourth season, and productivity and fruit yield increase until about the 10^th year when it levels off. Under good management and care, fruit trees can produce for decades.

Plant Care

Watering

It is critical to provide adequate irrigation for young plants and also during fruit bud formation in the fall. Drip irrigation is very helpful to ensure consistent, adequate water for the long production season. On average, plants that are 1 year old require about 3.5 gallons of water per week. Each year of growth doubles the weekly water demand (e.g., 2-year plants require about 7 gallons of water per week), up to a maximum of 35 gallons of water per week. Weekly watering is recommended over daily watering. As trees increase their root systems each year, the need for hand-watering decreases, depending on the season. In dry years, watering is still required for older trees.

Fertilization

Unlike most trees and shrubs, young citrus trees may be fertilized during their planting year, when new growth starts. Avoid fertilization after June, which would cause new growth that may be damaged by winter cold. Nitrogen is the most import nutrient; the number of flowers formed is proportional to the nitrogen status of the tree. Commonly seen nutrient deficiencies are zinc, magnesium and iron chlorosis, often associated with growing citrus on high pH soils.

Organic fertilizers such as compost, fish emulsion, composted poultry litter or manure, worm castings, and blood or bone meal originate from living organisms. They are far more environmentally sustainable and safe than traditional synthetic fertilizers. They naturally release nutrients more slowly and over a longer period of time. When applying organic fertilizer, it is important to use in unison with compost, cover crops, and crop rotation, which all work together to build soil health. Learn how to convert inorganic fertilizer recommendations to organic fertilizers here.

Alternatively, a synthetic fertilizer may be used. For newly set trees, about 6 weeks after planting, apply ½ pound 13-13-13 per tree. Beginning in mid-March of the following year, apply 1.5 pounds of 13-13-13 per year of tree age (i.e., 3 pounds for a 2-year-old tree, 4.5 pounds for a 4-year-old tree), scattered over the root system and watered in. Increase the amount by 1.5 pounds every year until the tree reaches maturity at 10-12 years. Mature trees should receive about 15 pounds of fertilizer every year in early spring. If an organic fertilizer is preferred, compost, aged manures and blood meal are good slow-release nitrogen sources. Rake back the mulch, scatter fertilizer material evenly over the root system, and reapply mulch.

Weeds

Organic mulch will control most of the weeds; hand-pull weeds close to the plant and reapply mulch as needed, not allowing the mulch to touch the trunk. It is important to keep a 3- to 5-foot weed-free area around each tree to prevent competition for nutrients and moisture.

Freeze Protection

Temperatures between 20-30 degrees F for more than 5 hours will cause fruit damage, while temperatures below 20 degrees F for more than 5 hours can kill some trees. Reduce freeze damage by controlling pests and diseases to keep trees healthy; by clearing the ground around the tree from mulch, grass, and weeds; and by covering the tree with a plastic tent during freezes. As daytime temperatures moderate, it is essential to remove plastic coverings before the sun can overheat and damage the tree. Bare ground under trees allows for greater absorption of the sun’s heat. Young trees (4 years or younger) can also be banked with soil up to 15 inches up the trunk, or wrap the trunk heavily with cloth to insulate. Remove soil banks or wrappings after the last freeze date.

Pruning

The purpose of pruning young, nonbearing trees is to shape the tree and develop main supporting branches that are distributed around the tree before growth starts in the spring. If possible, select a tree 2-4 feet tall with a branching framework already in place. If nursery-pruned citrus trees are not available, trees should be pruned at planting time. After pruning, the top of the tree should have 3-4 evenly spaced branches in an upward growing pattern starting at 18-24 inches above the ground. Growth below these inverted umbrella-shaped branches should be removed. After creating this branching framework, some pruning is needed during the first three years for citrus trees. See Figure 7.

Pruning of older trees should be done in mid-winter (January and February) to thin out thick growth and to remove dead or crossing branches; branches touching the ground; and long, vigorously growing shoots (especially those growing from the soil line). Additional pruning may be required to remove branches damaged by disease or freeze. When pruning, cut flush with the trunk to avoid leaving a stub. Unnecessary pruning may reduce fruit production.

Insect Pests and Diseases

Some citrus varieties are more susceptible to certain diseases and insects. When planting few citrus trees, they may not require insect pest management measures as they may be naturally controlled. The key citrus insect pests are aphids, scales, Asian citrus psyllid, mites, root weevils, leaf miners, and leaf-footed bugs. Citrus trees are also susceptible to fungal diseases (e.g., anthracnose and citrus scab) and bacterial diseases (e.g., citrus canker and citrus greening). Prevention and regular monitoring can help identify symptoms of these insect pests and diseases to allow for early diagnosis and management. Generally, recommended tools for disease prevention are using mulches; avoiding overhead irrigation; adequate pruning and plant spacing; and weed control. See Table 3 to aid in diagnosis and management of some common citrus insect pests and diseases.

Table 3. Organic and Natural Management for Common Citrus Insect Pests and Diseases

Harvest and Storage

In general, citrus is ready for harvest in the fall and winter when the fruit has turned from green to the optimal ripeness color. To harvest citrus without damaging the plant, gently pull the fruit off the stems by hand or cut the stem of the fruit with shears. During fruit production, citrus may be harvested every week for 3-5 months, varying by variety. Be sure to harvest citrus fruits before they are exposed to freezing temperatures. Citrus fruits left on the tree develop more color and improve quality with exposure to low temperatures, but extended freezing temperatures may freeze the fruit. Harvest fruit before the end of February so as not to reduce blooms and fruit set for the next year’s crop.

Citrus can be stored for a few days at room temperature, or in the refrigerator for several weeks. Preserve citrus by juicing the fruit and freezing peels or zest. Some citrus can be used to make marmalades or curd, which can then be canned.

Citrus are Nutritious and Good for You

Rich in Vitamin C

Important for bones, skin, blood vessels

Good source of dietary fiber

Important for bowel health, lowering cholesterol, controlling blood sugar, and maintaining a healthy weight

Excellent source of folate

Helps to maintain healthy cell growth and function

Recipes

Taste-testing ideas: citrus slices, citrus juice, lemonade or limeade, citrus salad, citrus popsicles, citrus smoothie, dehydrated citrus slices and rind

Other websites with many citrus recipes:

USDA MyPlate Kitchen: Oranges, Lemons, Limes

Produce for Better Health Foundation: Oranges, Grapefruits, Lemons, Limes

SNAP-Ed Oregon: Oranges

Sources

• LSU AgCenter, Louisiana Home Citrus Production
• LSU AgCenter, The Louisiana Home Orchard
• University of Florida IFAS Extension, Citrus Culture in the Home Landscape
• University of Florida IFAS Extension, The Satsuma Mandarin
• Texas A&M AgriLife Extension, Fruit & Nut Resources: Citrus
• Texas A&M AgriLife Extension, Texas Citrus and Subtropical Fruits: Home Fruit Production-Grapefruit
• University of Georgia Extension, Citrus Fruit for Southern and Coastal Georgia
• University of California Agriculture and Natural Resources, Agriculture: Pest Management Guidelines for Citrus
• Morton, J. 1987. Orange. p. 134–142. In: Fruits of warm climates. Julia F. Morton, Miami, FL.
• Morton, J. 1987. Lemon. p. 160–168. In: Fruits of warm climates. Julia F. Morton, Miami, FL.
• UMass Extension Vegetable Program: Disease, Insect, and Mites Fact Sheets
• Alabama A&M & Auburn Universities Extension, Crop Production
• University of Georgia Extension, How to Convert an Inorganic Fertilizer Recommendation to an Organic One, Circular 853