Citrus trees have been a commercial crop in Arizona for more than one hundred years, but are popular in the home garden, too. Our weather produces some of the best-tasting citrus. The warm spring and summers help the sugars in the fruit produce a sweet and tasty crop. Citrus in Arizona are grafted onto the sour orange rootstock, which helps produce a sweet fruit. Left unchecked, the sour orange rootstock found at the base of the tree sometimes begins growing branches. Prune off any rootstock branches that may grow below the grafted area. If left to grow, the rootstock invades the main tree and prevents production of healthy fruit. The rootstock growth is noticeable since it has major thorns on its stems.
A citrus tree is an evergreen that retains its foliage year round. Citrus trees do not go dormant like deciduous trees. However, there is a reduction of foliage growth during the winter months. When the weather warms again in March, a new flush of shiny leaves appear. Citrus trees produce spectacular fragrant, white blossoms in late February or March. The aroma from a mature citrus tree fills the air. A mature citrus tree produces thousands of blossoms, though only about two percent of these result in edible fruit. The fruit develops after blooming, over a period of three to four months. Citrus trees retain their fruit, and the longer the fruit is on the tree, the sweeter it becomes.
Citrus, which include oranges, grapefruits, lemons, limes and specialty varieties, tolerate our hot summer sun, but sometimes they might experience sun-burnt foliage. Some varieties tolerate hot climates better than others. Choose varieties that are best suited to extreme sun and heat. Also, bear in mind that if the foliage is pruned high on the tree, exposing the trunk, sun burning can occur. Allow the plant leaves of a mature citrus tree to grow closer to the ground, protecting the tree from scorching summer sun.
Citrus enjoy warm microclimates, safe from freezing temperatures. Choose a protected area, preferably on the south or west side of your home. If you live in a low-lying area or along a desert wash, avoid growing citrus in your yard, as cold air sinks and can damage trees during a frost. Check your neighborhood for mature, healthy citrus. If you observe healthy trees with ample fruit, you should be safe to plant your own. Most citrus are hardy to temperatures as low as the mid-twenties, Fahrenheit. Kumquats are the hardiest, whiles limes are the most sensitive to frost. When locating a suitable place in your landscape to install a tree, make sure you have enough room for it to mature. If space is an issue, consider planting a dwarf variety.
Dig the planting area at least twice the width of the root ball. Mix desert soil with organic soil amendments such as mulch, manure, or compost. Citrus trees thrive in areas where they are allowed to develop deep roots, so plant them in an area with good drainage. If you find caliche when digging, penetrate the hard surface with a jackhammer or digging tool. Plant the tree in the soil at the same height in the ground as it was planted in its container. Be careful when removing the plant from its container, as citrus roots can be fragile. Backfill mixed soil into the hole and immediately irrigate. If the plant settles a bit, add more soil. Do not fertilize a newly planted citrus tree.
Irrigation and Leaf Drop
Irrigate citrus often to help prevent salt accumulation in the soil near the trees’ roots. Water plants once per week during the winter months and two to three times a week during warmer weather. Always water generously to encourage plants to develop deep, healthy roots and dry out between irrigation cycles. If you notice the leaves turning yellow, then the trees are probably receiving too much water. It the leaves start to droop and curl during the hottest part of the day, this is an indicator that they need more irrigation. Sometimes, leaves start to drop during the winter months—this is normal and occurs prior to new spring growth.
Citrus should be fertilized several times a year. Apply the first application in early March, before blooms appear. Nitrogen, phosphorous, potassium, sulfur, and calcium are needed for optimum growth. Use a slow-release citrus fertilizer purchased at a garden center. Apply fertilizer evenly throughout the tree basin and extend out to the drip line of the tree, and then water it immediately. If fertilizing citrus in their first year, give a light application or no fertilizer at all. If there are blooms on the tree, wait until after blooming before applying fertilizer. Otherwise, you may shock the tree and cause the blooms to drop early without setting fruit. Apply a second application of fertilizer around Memorial Day and a third application near Labor Day. Do not fertilize trees after October. You don’t want to produce new growth and have the foliage freeze if temperatures suddenly drop.
Iron deficiency is a problem with citrus, and is indicated by yellow leaves with green veins. To correct it, add iron chelate fertilizer to the soil. When using a fertilizer high in iron, apply it according to the label and follow all directions thoroughly. Iron needs warm temperatures to be absorbed by plant roots. Also, be aware that citrus growing in sandy soils requires more water and fertilizer than trees grown in soils high in clay content.
Fruit Production, Pests, and Related Problems
Citrus take about two years to start producing fruit, regardless of the size of the tree when planted. The fruit production is also related to variety and vigor of the tree. Once citrus fruit is removed from the tree, it does not ripen further. So it is important to pick the fruit at the right time.
It is normal to have some dead wood and twig dieback on citrus trees, observed in the early spring, and particularly after a cold winter. When new leaves appear in March, prune back any frozen branches or twigs. Selectively prune twig dieback in the interior of the tree.
When the weather warms up in June, it is normal for some citrus fruit to drop from the tree. Excessive fruit drop on mature trees is caused by poor drainage or occurs more frequently on trees planted in low-lying areas. The amount of fruit drop depends on specific varieties. Seedless varieties of oranges may drop more fruit than the heavily seeded varieties. Grapefruit and some oranges may drop fruit naturally to increase food supply. Keeping citrus well irrigated during the onset of hot temperatures helps prevent fruit drop.
Fruit splitting occurs on some orange and grapefruit varieties. Tangerines and tangelos have a lower chance of fruit splitting. This happens during periods of high temperatures combined with high humidity and rainfall in August. If the citrus fruit is sunburned, the incidence of fruit splitting is higher. It also occurs if there is a heavy load of fruit on the tree. Proper irrigation and fertilization of the tree reduces the incidence of fruit splitting.
If leaves on the citrus tree suddenly curl up and produce a crinkled, distorted appearance, thrips may be feeding on the foliage. Thrips are very tiny, fast moving insects that are barely seen when they appear on new foliage. Fortunately, this is only cosmetic and thrips eventually disappear when the weather warms up.
Since citrus trees have edible fruit, always use topical insecticides carefully and sparingly, and only when fruit or flowers are visible. Do not use systemic type insecticides on citrus because the chemicals can travel though the plant and be absorbed by the fruit. If insects like aphids, scales, or mites are feeding on the tree, use a household spray of water with mild dish soap to minimize the infestation. If it continues, use a solution of one percent light horticultural oil, sprayed carefully on the leaves.
Citrus Diseases and Related Problems
Fortunately, our desert environment does not attract too many serious citrus diseases. Relatively low humidity stops most diseases in their tracks. However, be aware of a few problems that may affect citrus.
Phytophthora root rot. Root rot is caused by two soil microorganisms. The rot is found at or just below the soil level. Cracking on the side of the bark and gumming around the trunk are signs of this fungus disease, and advanced stages produce yellow, sparse foliage. Trees may eventually die due to the girdling action of the fungus.
Fortunately, most citrus trees are grafted to disease-resistant rootstock. Good planting practices help avoid problems with this disease, so make sure the bud union of the grafted tree is at least four inches above the soil level. Also, provide planting holes in well-draining soil. Do not let irrigated water sit around the crown of the citrus tree. Additionally, avoid planting in soils filled with caliche; break through the caliche barrier at planting time.
If Phytophthora root rot is still a problem, portions of the diseased bark will need to be removed, and fungicide applied. First, scrape off visible fungus on the trunk of the tree. Then, treat it with Subdue fungicide at full strength—paint the fungicide on the visible rotted areas on the trunk. Follow the manufacturer’s label before applying this chemical.
Rio Grande gummosis. Rio Grande gummosis attacks grapefruit and is common in older trees. This disease got its name because it was first discovered on grapefruit in Texas growing near the Rio GrandeRiver. This fungus enters trees through broken or dead branches. Initial symptoms appear as a small drop of gum on the surface of the bark. Then the bark may slightly split apart. Other symptoms include a sap that oozes from a crack in the bark or trunk leaving a large, gummy deposit along its length. There is no fungicidal treatment for this disease except to remove the tree’s infected areas. If infected areas cannot be cut away without removal of the entire tree, then you will have to decide whether you are willing to remove the entire infected tree.
Spiroplasma citri. Spiroplasma citri, more commonly known as stubborn disease, affects oranges, mandarins, and grapefruits. It is more prevalent in younger trees but may appear anytime in the life of a citrus tree with varying degrees of symptoms. In some cases, only a part of the tree shows signs of the disease. Symptoms include stunted growth, misshapen trees, abnormally small fruit or the absence of fruit, twig dieback, and multiple bushy shoots. Stunting is common in younger trees and symptoms are more pronounced in hot weather. The disease is usually spread by a leafhopper insect or by improper grafting or budding of the trees.
There is no control for this disease. However, trees purchased from reputable garden centers are propagated from disease-free rootstock, minimizing problems. Infected trees should be removed immediately and replanted with healthy trees to avoid spreading the disease.
Types of Citrus
The most common citrus grown in Southwest desert landscapes are Arizona sweet oranges, tangelos, grapefruit, lemons, limes, mandarins and dwarf citrus. Purchase good quality plants from local nurseries. The best times to plant citrus are March and April. However, in warmer areas, citrus can be planted through September.
Oranges. The Arizona sweet varieties include Early Hamlin, Pineapple, Marrs, Diller, and Trovita. These oranges are easy peelers, great juicers, and more tolerant to frost than other varieties. Early Hamlin is an early ripening variety, is very hardy, and doesn’t produce many seeds. The tree is medium to large.
Pineapple is also grown for its juice. It ripens early in the season, is medium in size, and is not as easy to peel as the other varieties. It produces a lot of fruit one year and then tends to produce a lighter crop the following year.
Marrs is an early maturing, semi-dwarf tree. This is a good choice if you have limited space in your landscape. It is a productive fruit producer early in its life, and though its fruit is not easy to peel, its quality is good.
Diller is also an early ripening variety. Its fruit is sweet and juicy and it produces a lot of seeds. This is a good choice if you are interested in a juice orange.
Trovita is one of the hardier varieties, and produces ample fruit. It is also a good juice orange with few seeds and is easy to peel. It produces a heavy crop one year and a light crop the next.
Tangelos. Tangelos are a mixture of the mandarin and grapefruit. They usually have loose skin and are very easy to peel. Known for their sweet, juicy fruit, they are distinguished from the orange by a thick knob at the top of its skin. The tangelo is also one of the hardiest citrus. The two varieties that do well in our climate are the Minneola and Orlando.
Minneola has a distinctive pear shape and is easy to peal. The bright orange fruit matures in January through March and has an extremely tasty flavor. The fruit becomes sweeter the longer it is left on the tree. Since this tree can freeze in cold temperatures, plant it only in warmer locations and protected areas. Minneola is a large tree with big, glossy, green leaves. The fruit has a large neck and bell-shaped appearance. It peels easily and is very juicy. Orlando has fruit that is medium in size without a pear-shaped neck. The fruit ripens from November through January, is mildly sweet and harder to peel, but is one of the best tasting. The foliage has large, deep green, prominent leaves that are slightly cupped. Orlando is hardier than the Minneola.
Grapefruit. The hybrid grapefruits commonly grown in today’s landscapes are actually a cross between the pomelo and a common grapefruit. A pomelo is a large, exotic ancestor of the common grapefruit. It originated in Asia and its fruit resembles a grapefruit. Its flowers are beautiful, fragrant, and ivory-white. The grapefruit develops sweet fruit in areas with warm summer temperatures.
There are two types of grapefruit, one with white inner flesh and one with pink. The demand for pink grapefruit is high, but there are several white varieties that are extremely sweet. Marsh, a seedless grapefruit, is one of the most common white varieties. The fruit is ready to harvest in December, but leaving it on the tree longer produces a sweeter, tastier fruit. The tree bears fruit consistently throughout the season.
Duncan is one of the oldest white varieties on the market, and also one of the best tasting. It has large, round, juicy fruit, and is full of flavor, but it has given way to other varieties with fewer seeds.
Red blush is a seedless variety with large pinkish flesh. The fruit is ready to harvest in December, but becomes sweeter and lighter in color the longer it remains on the tree.
Lemons. In the Southwest desert, the lemon tree is a wonderful specimen, especially when it is covered with bright yellow fruit ready for harvest. A true lemon tree can grow ten to twenty feet tall, and in warm climates, are usually heavy fruit producers. In these warm climates, the fruit is harvested in late winter through early spring.
“When life gives you lemons, make lemonade”. —Unknown
The Eureka variety has a tougher, bright yellow rind and is more sensitive to frost than other varieties. It is one of the more popular lemon varieties commercially sold. The tree is thornless with seedless fruit and bears fruit for most of the year.
The Lisbon produces fruit somewhat comparable to Eureka, but the tree is hardier and more heat tolerant. The fruit is borne inside the canopy of the tree, which helps shelter it from cold temperatures. This variety is a fast grower with dense, lush foliage, which means that it needs regular pruning to help it keep its shape.
Ponderosa is an ornamental hybrid of the lemon and citron fruit. It is an ever-bearing tree that produces large, almost grapefruit-sized, juicy fruit with thick rinds. The fruit is full of seeds and hard to peel. Watch out for the tree’s thorns, and before planting, consider that it is more sensitive to cold than other lemon varieties.
Limes. The lime is the smallest member of the true citrus family and is native to Southeast Asia. It is one of the most varied groups of all citrus species. The lime is a delight among gourmet chefs, although it is rarely used on its own. Limes are second to lemons as flavoring agents for food—think of the famous key lime pie. Limes are not as hardy as lemon trees and require some protection from frosts. In colder climates, the lime can be grown as a container plant in protected areas. Limes develop their flavor during the hot summer. Fruit is harvested from trees beginning in December when the outer skins turn green.
There are three basic types of limes. The Persian lime is grown mostly in Florida, and has glossy, green leaves. It is considered hardier to cold than some of the other limes. The Bearss lime is grown mostly in California, is fast-growing, has a broader canopy and is also hardy. A third lime, the Mexican lime, is grown in Mexico and other tropical climates. It is also called the bartender lime, and in Florida, is sometimes referred to as the key lime. This lime is fast-growing and thornier, produces aromatic fruit, and has smaller leaves. It is more sensitive to cold than the Persian or Bearss limes.
Mandarins. Mandarins are one of the most popular fruits sold today. They are smaller in size, easy to peel, and their inner segments separate with ease. They are juicy, and while some varieties have seeds, others are seedless. Cold nights and warm days produce the beautiful orange color in the fruit. The vitamin A found in the fruit produces a compound known as carotenoid, which also gives the fruit its orange color. Mandarins and tangerines are basically the same fruit, but while a tangerine is a mandarin orange, not all mandarins are tangerines.
Mandarins are one of the hardiest citrus; however the fruit is still sensitive to frost damage. The fruit ripens beginning in early fall and most fruit should be harvested before frosts occur. The Clementine variety ripens between November and January. It has lots of seeds, a deep, orange color, and an appetizing flavor. As the tree ages, it loses its susceptibility to frost damage. Clementine is an alternate bearing tree—one year it produces a heavy crop, and the next season a lighter crop. Clementine should be planted with other tangerine or tangelo varieties, or the sour orange tree to ensure cross-pollination and production of fruit. The fruit needs to be picked as soon as it ripens.
Dancy is harvested early, usually before Christmas. The fruit is medium in size and very sweet. This variety is a quick grower, is also an alternate bearing tree and produces some thorns and a lot of seeds.
Fairchild is a medium-sized tree with almost no thorns. It produces flavorful fruit in November and is a heavy cross-pollinator. This mandarin variety is also an alternate bearing tree.
Kinnow is a hardy variety and easy to peel. It has a high sugar content and sweet fruit that matures late in January. And like all other mandarins, this variety is an alternate bearing tree.
Dwarf citrus. Dwarf citrus are smaller-sized citrus trees that produce delicious fruit. These trees are grafted on specific dwarfing rootstocks. They are excellent to use in areas that lack adequate space for a larger citrus tree to grow. They are also good to use in larger containers. Some trees that are marked as dwarfs are actually semi-dwarfs. The dwarf size is anywhere from 25 to 75 percent smaller than a common citrus tree at maturity, and can be stunted further if grown in containers. Some dwarf citrus, however, can reach heights of five to seven feet tall or more, depending on the variety. They require full sun with a warm, southern exposure. Make sure the soil has good drainage. Keep the soil moist and don’t let the tree dry out. Dwarf citrus like to be fertilized. Apply a citrus food about three times per year, scheduling feedings around Valentine’s Day, Memorial Day, and Labor Day.
Citrus trees create an amazing landscape element that has beautiful, dark, evergreen foliage, fragrant spring blossoms, and colorful, delicious fruit. You have the choice of so many varieties of citrus, so research them all and purchase citrus trees that will make the most pleasing and practical addition to your landscape.