Fruit and Nut Review

Citrus and Kiwifruit

Part I: Citrus

Citrus fruits are among the most popular fruits produced in tropical and subtropical areas of the world. Most citrus originated in China and southeast Asia; lime probably developed in India.

Members of this group are small trees or shrubs. This group contains orange, grapefruit, lime, lemon, and tangerine. The kumquat is closely related and has been used in breeding programs to produce the limequat, orangequat, and citrangequat.

The actual fruit is a berry made up of 10 to 13 segments called locules that are filled with juice sacs containing sugars and acids. If sugars prevail, the fruit may be very tasty, as are tangerines and most oranges. If acids prevail, the fruit may be quite tart, as are lemons and limes.

Lemons and limes are often used as seasonings in cooking. Their juices may be diluted with water to which sugar has been added to make a refreshing drink. Citrus fruits are high in vitamin C.

Adaptation

Since citrus fruits are tropical or subtropical in origin, winter protection is a must. The lowest temperature at which growth in citrus occurs is 55 °F; the highest is about 100 °F. The best temperature range is 70 to 90 °.

Hardiness differs according to species and sometimes variety. The tree can usually withstand temperatures 3 to 4 degrees cooler than the fruit. Ripe fruit can withstand lower temperatures than green or immature fruit. The following chart indicates the lowest temperature a citrus tree can withstand without damage. Remember, fruit injury occurs at temperatures several degrees warmer.

The duration of the cold period is as important as how low the temperature gets. It usually takes 3 to 4 hours at 27 to 28 °F to injure naval oranges. However, only 30 to 60 minutes at 29 °F will injure small lemons. To prevent cold injury to citrus, a greenhouse conservatory, or "Florida Room" is required. With recent severe winters and late spring freezes, many outdoor citrus plants have been killed back to the graft union. The understock may regrow, producing a seedy, sour, inedible fruit.

When grown outdoors, citrus plants require a well-drained soil rich in organic matter. In containers, most commercial potting soils are adequate. The soil pH should be slightly acid to near neutral. Citrus plants grow best in full sun.

Variety Selection

Citrus plants can be some of the most rewarding plants for the home gardener when you consider qualities of citrus. They produce a deep emerald-green foliage, white, sweet-smelling flowers, and highly colored fruit. Even citrus that is not edible can be grown as an ornamental. Plant sizes range from small shrubs (such as the Meyer lemon) to large trees (such as the grapefruit). Provided you meet the climatic requirements (winter protection, light) and space requirements, you can grow any citrus variety.

Citrus plants are self-fruitful -- only one plant is required for fruit production. However, cross-pollination enhances fruit set and increases production. If space permits, grow at least two varieties.

Orange (Citrus sinensis)

The only orange variety recommended for growing outdoors along the Gulf Coast is the "Washington Naval." This variety requires a protected area such as the south side of your home. The most distinctive fruit feature is the presence of the navel, a small, rudimentary fruit embedded in the blossom end of the orange. Other distinctive features are its lack of seed, thick skin, ease of peeling, ease of separation of segments, and its richness of flavor. The fruit color is deep orange. This variety may be grafted onto the trifoliate orange or Troyer rootstock. Grafting onto the trifoliate orange increases its cold hardiness.

For growing in greenhouses or a Florida room, you may also select Robertson Naval or Summernavel in addition to the Washington variety. For common oranges, consider Hamlin, Marrs, Parson, Pineapple, and Valencia. For sour oranges, consider Bouquet, Chinotto, or Seville. Sour oranges are excellent for marmalades.

Grapefruit (Citrus paradisii)

Recommended varieties of grapefruit include Duncan and Ruby Red, the most widely planted variety. The fruit is medium-sized and has few, if any, seed. It is light yellow with a red blush at maturity. The fruit holds well on the tree. Harvest time ranges from December through May. It may be grafted onto the trifoliate orange understock. Duncan is a seeded fruit and medium in size. For growing in greenhouses or a Florida room, you may also select Marsh.

Lime (Citrus aurantifolia)

Limes do not tolerate cool climates and are not normally planted farther north than Florida. A hybrid between lime and kumquat (limequat) is more cold hardy and may be grown outdoors along the Gulf Coast.

Limequats are similar in appearance and can be used in the same way as limes. The fruit is not as bitter. It is pale yellow and about 1 inch in diameter when mature. Standard trees may reach 6 to 10 feet tall, with dwarfs reaching 3 to 5 feet. Lakeland and Eustus are good varieties of limequat. For growing in greenhouses or a Florida room, you may also select the lime varieties of Bearss (Tahiti or Persian), Mexican (Key), or Rangpur.

Lemon (Citrus limonia)

Lemons, like limes, are sensitive to cool climates. The variety most often grown along the Gulf Coast is Meyer because it is the most cold hardy of the lemons. Meyer is sweeter and has less acid than other lemons. It does require winter protection. For growing in greenhouses or a Florida room, you may also select Eureka, Improved Meyer, Lisbon, or Ponderosa in addition to Meyer.

Mandarin Orange (Citrus reticulata)

The Mandarin orange is also known as satsuma and tangerine. The fruit is smaller than regular oranges; the skin is a deeper orange and is easily removed from the fruit.

Kimbrough is probably the most cold hardy of the Mandarin oranges. It was selected from seedlings of open-pollinated Owari satsumas that survived freezes.

For growing in greenhouses or a Florida room, you may also select Owari, Armstrong Early, Ponkan, and Satsuma.

Planting

Plant citrus the same as other fruit trees if planting outdoors. If planting in containers, select ones large enough to accommodate the mature size of the citrus plant you choose to grow. Plant as you would other container plants, but be sure to set the plant no deeper than it grew in the nursery.

Fertilizing

You must maintain a regular fertilization program for citrus. For the Gulf Coast, three applications per year between February and September are usually sufficient for older trees.

In the absence of a soil test, for the first application use a complete fertilizer such as 6-12-6, 8-8-8, or 13-13-13. Apply the equivalent of 1/2 pound of actual nitrogen per tree at this time. For the remainder of the fertilizer applications, use ammonium nitrate. Apply about 1/2 pound of actual nitrogen per tree at each application.

For trees less than 3 years old, apply about 0.1 to 0.2 pound of nitrogen per tree at each application. Fertilize young trees four or five times between February and September.

If you are growing your citrus in containers, use houseplant fertilizer. For the application in January or February, select a houseplant fertilizer high in phosphorus (the middle number). At other times, use an even analysis such as 20-20-20. Follow the label instructions for rates and frequencies.

Watering

Water is important for citrus. Drought during flowering causes fruit not to set. A lack of water at other times causes fruit to drop and yields to be lower. Extended droughts can cause leaves to drop and plants to die. Care in selecting the planting site is important, because citrus plants cannot tolerate wet feet and standing water can kill them. Plant in well-drained locations and water often and deeply during dry periods.

Pruning

There are several reasons for pruning citrus trees. The first pruning should be to balance the shoot-growth potential with the root's supportive capacity. This increases the chances for a successful transplanting.

Pruning to create a scaffolding network helps assure maximum fruit yield. Scaffolding branches should be no lower than 18 inches from the ground. Select three or four branches evenly spaced about the main trunk and between 18 inches and 48 inches above the ground. These will be the tree's primary branching structure. Remove all other branches.

Prune to remove any dead, diseased, or damaged limbs. Also, remove any limbs that may touch and rub. Cold-damaged wood may not be noticeable until plants begin to grow in the spring. Do not make any cuts below the graft union.

Propagating

Many citrus plants are started from seed; however, if grown in containers, these seedlings may never form flowers and fruit. The time from seed to fruit in the field may be 7 to 8 years -- a lot of time to devote to trees that may not have quality fruit. For this reason, most citrus plants are started from cuttings or grafted onto a seedling trifoliate orange understock.

Citrus plants may be grafted using the "T" bud, the inverted "'T" bud, and the cleft graft methods. This may be done in the fall or the spring. Budding is best done when the bark is slipping.

Pests and Diseases

Citrus may be attacked by many pests, including the white fly, the orangedog caterpillar, and spider mites.

Disease problems include scab, melanose, and sooty mold. A regular spray program is recommended to reduce the chances of these pests' becoming severe problems.

Harvesting

Citrus fruits mature at various times of the year. Varieties of oranges and mandarins may ripen in October and November of the year in which they flowered. Late varieties may fruit in February and March of the year following flowering. It is not uncommon to have flowers, immature fruit, and ripe fruit on the plant at the same time.

The only sure way to determine maturity is to taste the fruit, because color is a poor indication of maturity, since many citrus fruits become sweet months after the rinds have developed color. Lemons and limes are exceptions. Since these are grown for their acid flavor, harvest any time the fruit reaches a usable size and juice content is adequate.

Once mature, many citrus fruits may be stored on the tree for several weeks and picked when needed. Mandarins are an exception. Mandarin fruit does not store well on the tree. Most citrus can be stored in the refrigerator for several weeks. If left at room temperature, the fruit may develop an off-flavor, wither, and become unattractive after about a week.

Citrus-Related Fruit

The kumquat (Fortunella species) is related to citrus. Some have been used in breeding programs to develop fruit such as the limequat, orangequat, and citrangequat.

Kumquats are more cold hardy than citrus, being able to withstand temperatures as low as 18 degrees Fahrenheit. Kumquats may be used as garnishes or made into marmalade. Those with a high sugar content may be eaten fresh. To eat, roll and squeeze the fruit between your fingers to combine the sweet flavors of the skin with the tart flavors of the pulp. Nagami and Meiwa are varieties of kumquat.

Part II: Kiwifruit

Kiwifruit production in the home vineyard may not be practical or feasible in Mississippi. There is no Mississippi research to support or refute its potential, and growing kiwifruit should be on a trial basis only.

Kiwifruit (Actinidia chinensis Planch) is native to China and southeast Asia. It is a vigorous, deciduous fruiting vine reaching heights of 30 feet or more. There are about 50 other species in this genus, all of Asian origin. Some are grown for their ornamental value, but only a few are grown for their edible fruits (Actinidia chinensis, A. arguta, and A. kolomikta). The best of these edible fruits is undoubtedly Actinidia chinensis, which is also known as Chinese gooseberry, yangtao, kiwifruit, or kiwi.

Horticulturists in New Zealand developed the kiwi as we know it today. The first commercial vineyards in New Zealand were planted around 1930.

"Kiwi" was coined by New Zealand businessmen wishing to have the fruit gain acceptance by their import markets. No doubt it reminds them of their native, flightless bird known for its brown hairlike feathers and oversized eggs.

The fruit of the kiwi is about the size of a small goose egg with a brown, hairy skin. The flesh has a bright green color and a berrylike flavor. When you cut a kiwi in cross-section, you can see a decorative circular pattern of black seed and light-colored rays.

Adaptation

Temperature -- The kiwi may be grown in most areas of the United States where temperatures do not drop below 10 degrees Fahrenheit. The vines and flowers are susceptible to damage from late spring frosts or freezes. The fruit, which requires about 240 frost-free days to become sweet, may be damaged by early frosts in the fall. Recent severe winter freezes and late spring frosts raise questions about the suitability of this fruit for Mississippi.

Kiwi varieties have chilling requirements as do many other fruits. These requirements range from 400 to 800 hours. With mild winters, the vines may retain the foliage all winter and fail to flower the following spring. Incompletely dormant vines do not respond well to pruning.

Wind -- Protect kiwi vines from strong winds that can snap young branches from the vine and injure fruit where it rubs against the vines. For this reason, planting windbreaks is recommended. Planting the vines along walls or solid fences may serve the same purpose as windbreaks.

Site selection -- Kiwi vines grow best in full sun though they may tolerate partial or light shade. The soil should be well-drained and rich in organic matter. The pH should range from 5.5 to 7.0, with 6.5 being ideal. Kiwi vines do not tolerate soils with high soluble salts. Kiwi vines require much water. Salt-free water should be available.

Variety Selection

Kiwi vines produce male flowers on one vine and female flowers on another. Plant at least one male and one female vine. Commercially, one male vine is planted for eight female vines. For the homeowner, if the vines are productive, only two vines will be required, one male and the other female.

Kiwi flowers are pollinated by insects. Because the female flowers have no nectaries, bees and other insects are not attracted to them, but bees enter and pollinate female flowers while searching for the pollen in the male flowers. (Bees apparently are unable to distinguish female flowers from male (kiwi) flowers.)

Since other plants flowering at the same time as the kiwi may offer a better pollen and nectar source, locate a beehive near kiwi vines. Planting the vines away from other flowering plants increases the chance for good pollination.

Fruit size is related to good growing conditions and to the number of seed developing in the fruit.

Male Varieties

Male varieties are used only as a pollen source and do not produce fruit. Four varieties of male vines may be used as pollinators: Manteau, Tomuri, Chico Male, and California Male. Manteau is used most often because it has a long blooming period. Although it blooms earlier than the female Monty and Hayward varieties, there is usually enough overlap for good fruit set.

Tomuri flowers late and can also be used to pollinate Monty and either of the Hayward varieties.

Chico Male is sometimes preferred as a pollinator for Chico Hayward. California Male may also be used as a pollinator for Chico Hayward.

Female Varieties

For homeowners, usually one or two female vines and one male vine are sufficient.

Abbott -- Vigorous vine bearing many small, early, round fruit with long, soft, dense hairs. Fruit is small unless thinned; medium chilling requirement.

Bruno -- Vigorous vine bearing many oblong fruit with dark, bristly hairs. Fruit must be thinned for good size; not for areas with a short growing season; medium chilling requirement.

Chico Hayward -- Fruit is large, late, oblong, pale greenish brown with fine, silky hairs; though of excellent quality, some fruit odd-shaped; light crop; does not need as much thinning as other varieties; indistinguishable from Hayward; preferred commercial variety; high chilling requirement.

Hayward -- Identical to Chico Hayward; originated in New Zealand; high chilling requirement.

Monty -- Vigorous vine bearing small to medium-sized, oblong fruit early; fruit must be thinned; generally lower quality fruit; flowers early; medium chilling requirement.

Tewi -- Moderately vigorous vine producing medium-sized, oblong fruit; early; low chilling requirement.

Vincent -- Vigorous vine-bearing fruit similar to Chico Hayward; flowers and ripens early; fruit must be thinned; low chilling requirement; may flower with as few as 100 hours of chilling temperatures; may be susceptible to damage from late frosts.

Planting

Kiwi vines are purchased as bareroot or container-grown plants. Since they are somewhat shallow-rooted, the planting hole need not be as deep as would be required for other fruiting vines.

Kiwi vines require a trellis or other support at planting time. If you are planting only two vines, one male and the other female, do not let them intertwine because it makes pruning more difficult. Space plants 20 feet apart within the row. Rows are often 12-15 feet apart.

Watering

The vigorous growth and abundant foliage of the kiwi vine demand lots of water. Water deeply and often in a basin that extends 5 to 6 feet around the vine. Water-stressed plants drop their foliage, exposing the fruit to sunburn and may not flower the following season.

Mulching is an excellent means to help reduce water stress. Keep the soil moist until harvest time and then reduce watering to help induce dormancy.

Fertilizing

Mature kiwi vines need about 1 pound of actual nitrogen per year. Apply the fertilizer evenly under the entire canopy of the vines. Since late fertilization may delay dormancy, do not fertilize after midsummer. Soil analyses may show a need for chelated micronutrients in some areas. Young vines are sensitive to overfertilization and require only 1/8 to 1/4 pound of actual nitrogen per year.

A suggested fertilization program is 1/8 to 1/4 pound of actual nitrogen the first growing season, 1/4 to 1/2 pound of actual nitrogen the second season, and 1 pound of actual nitrogen for the third and succeeding years. If you choose, split the annual nitrogen requirement into two or three applications and apply them evenly over the growing season. Be sure to make the last application no later than midsummer.

Pruning

Prune and train kiwi vines carefully. Without pruning, the vines quickly become a tangled, fruitless mass. There are two pruning methods for female vines: the fruiting lateral and the spur methods. The one to choose depends on how much room you have and how many plants you plan to grow.

Male vines are pruned differently; just remove about one half the growth after the male vine has flowered.

Fruiting -- Lateral Method

Most commercial growers prefer this method. The vines are trained to a five-wire trellis supported about 6 feet above the ground. Since the vines are vigorous, the posts should be at least 4 inches by 4 inches or the equivalent in a round post. Place a cross-arm on which to run the wires on top of the post. This crossarm should have a brace to the post to provide support. Set posts 16 feet apart, with vines planted 4 feet from each post.

Begin training by topping the main vine at a point 6 inches below the wires. Train the two most vigorous shoots that develop out the center wire, one in each direction. These vines are called cordons. The "V" formed by this first cut is stronger than the "T" that would be formed if the original cut were made even with the top wire.

First growing season -- Permit the cordons to grow the length of the wire. Fruiting laterals may be permitted to grow every 24 to 30 inches along the main cordons. Remove all other side canes. About midsummer, head the fruiting laterals back to 4 feet or prune them just to the outside of the last wire. During the first dormant season, count eight to 10 buds from the cordon and cut off the remainder of the vine. If you cut laterals to this length during the summer, you reduce the number of leaves that manufacture food for next season's flowers.

Second growing season -- After flowering, count out eight to 10 buds past the last flower and cut the vine. During the winter, cut the primary laterals just past the cane that fruited the previous year.

Third growing season -- Prune the second year laterals as you did the first year: all laterals that have fruited twice. Cut the newly formed fruiting lateral back to eight to 10 buds from the cordon. This begins the process all over again.

Spur Method

Where space is limited, the spur method is preferred. With this method, fruiting spurs develop from the main trunk or cordon.

First growing season -- Begin training by cutting the main stem to a height of 5 to 6 feet. Permit four cordons to develop, two at the uppermost level and two about halfway from the ground. Remove all other vines growing from the main stem.

As the cordons grow, tie them loosely to a trellis, wall, or fence. Permit vines to grow from the cordons. During the first dormant season, remove some of these secondary vines. Leave others spaced about 12 to 15 inches apart. Count out three buds from the cordon and prune off the remaining vine; these will be the fruiting spurs.

Second growing season -- Permit the spurs to flower and fruit. Also permit replacement spurs to begin to develop along the cordon. During the second dormant season, cut the one-year-old spurs to two buds past the last fruit cluster. Head the newly developed fruiting spur to three buds as was done to the one-year-old spurs the previous dormant season.

Third growing season -- Permit all spurs to flower and fruit. Permit the growth of replacement spurs. During the third dormant season, remove all spurs that have fruited twice. Leave two buds on last year's spurs. Develop replacement spurs.

Pests and Diseases

Kiwi vines are susceptible to root-knot nematodes that limit yields. However, vigorous vines show little damage from nematodes.

Oak root fungus has been reported to attack kiwi vines in southern California, and it could also be a problem in Mississippi. Other soil-borne diseases may be a problem in poorly drained soils.

Harvesting and Storing

Harvesting

Kiwifruit usually ripens in late October or November in hot areas, December in cooler ones. It should be picked hard and ripened off the vine much as a pear. The key is to know when the fruit is ready to pick. A change in color from greenish brown to brown usually is a good sign that it's time to pick. Another sign is when a few fruit begin to soften.

Kiwifruit are normally harvested twice. The first harvest removes the largest fruit, leaving the smaller ones to grow larger and sweeten. Fruit left on the vine too long soften and decay. They may attract birds.

A light frost (31 °F) will not damage the fruit and may even improve its quality. Temperatures lower than 31 ° ruin the fruit and make it inedible.

Storing

Kiwi ripen in a few days at room temperature. If you want to shorten the ripening time, store the fruit in sealed plastic bags with ethylene-producing fruit such as apples or bananas.

Unbruised kiwifruit may be stored for up to 6 months in the refrigerator if the air circulation is good and no ethylene-producing fruits are stored with them. Check often and remove fruit that begin to soften or decay.

Kiwifruit Relatives

Several close kiwi relatives produce delicious fruit and are very hardy. The tara vine or hardy kiwi (Actinidia arguta) may withstand temperatures to -20 °F. This vine is similar to the regular kiwi except the leaves are longer and more pointed.

As with the regular kiwi, male and female vines are required for pollination. The flavor is similar to the regular kiwi, but it is smaller and may be eaten, skin and all. It ripens on the vine in areas with 200 or more frost-free days.

Another relative, Actinidia kolomikta, is a slender deciduous vine with pink and white foliage. It is reported to withstand temperatures down to -20 to -30 °F. The flowers are fragrant. The fruit is small (3/4 to 1 inch long) and ripens over a long period (making it desirable for home vine yards).

By John Davis, Area Horticulture Specialist, John Braswell, Area Horticulture Specialist, and Freddie Rasberry, Extension Horticulturist

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Publication 1779
Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture. Published in furtherance of Acts of Congress, May 8 and June 30, 1914. Ronald A. Brown, Director