Citrus Update
2011 Improved Meyer Lemon
This picture was taken in September 2011. The tree has lost some leaves due to a leaf spot disease which is now under control.

My Citrus Story
My first try at growing citrus indoors was when I purchased a Calamondin orange tree at a local supermarket about 20 years ago. The tree grew reasonably well under my care and this encouraged me to find out more about citrus. So, I went to the local library and read everything I could on the subject. A few years later, I decided to try growing a sweet orange tree. I bought a 1 year old dwarf Trovita orange from California. When my tree arrived, I potted it up and over the next few months, it grew into a very beautiful tree. It bloomed profusely 2 years later and many fruits developed. Unfortunately, I had to move that same year and I wasn't able to take my pride and joy with me. Pictures of my tree can be seen here.


Buying a Citrus Tree
Potted citrus trees can be purchased at some garden centers in non-citrus areas. Trees are sold either as bare-root or in containers. Citrus trees should be purchased at a reputable citrus nursery that certifies its nursery stock free of diseases and insects. Before you purchase a tree, make sure you have the right growing environment for it. It is very important because not all citruses are the same.


Best Varieties for Beginners
There are many varieties of citrus trees that do well under indoor cultivation. The following are the best for beginners because acid fruits have a lower heat requirement for ripeness than sweet fruits.
Calamondin Orange
This plant is not a true orange. It is very productive and cold tolerant. The fruit is about 1.5 inches (3.8cm) in diameter, very juicy, highly acidic, with few seeds. The peel is deep orange, thin, sweet and edible. The fruit can be used to make marmalade and the juice can added to water and sweeten to make a tasty fruit drink. Fruit matures in about 8 months and holds on the tree for months. A varigated form is also available. Highly recommended for its toughness and ornamental beauty..
Improved Meyer Lemon
This plant is a lemon hybrid. The tree is almost thornless, productive, and blooms frequently. Flower buds are tinged with purple. The fruit is small to medium size, mildly acidic, juicy with excellent flavor. Highly recommended.
Pink Varigated Lemon
The tree has beautiful green and yellow varigated leaves. New growth and flower buds are pinkish-purple. The fruit is pink-fleshed with lemon flavor. Highly recommended for its ornamental beauty.
Persian or Bearss Lime
This tree is vigorous, few thorns, and bears fragrant blossoms and fruit all year in cool climates. The fruit is medium-small, acidic, and very juicy. Fruit is usually picked green, but it's yellow when ripe. Mature fruit doesn't hold well on tree. Highly recommended.
Eustis Limequat
This plant is a lime x kumquat hybrid. The tree is very productive and cold-tolerant. The fruit is medium-sized and has the flavor and aroma of a lime. Mature fruit holds on tree for a month or more.
Nippon Orangequat
This plant is a hybrid between a mandarin and kumquat. The tree is productive and very cold tolerant. The fruit is small, few seeds, juicy, acid with a sweet rind.


Planting
Citrus trees do best in soil that is well-drained and moisture retentive with a pH between 5 and 7. Soil-based potting mixes should contain pasteurized soil along with other amendments to improve drainage and aeration. Artificial soil mixes should contain some leaf mold, worm castings, or compost.
If you purchased a citrus tree that came in a pot, carefully slip it out of the container and examine the rootball. If the rootball is densely packed, it will have to be rootpruned and transplanted.
If the tree you purchased is bare root, find a pot that will accomodate the root system. Mound soil up in the center of the pot. Hold tree up with the roots spread out over mound. Add soil to the soil line on trunk then press down to release air pockets and water immediately. Add no fertilizer.


Watering
Knowing when to water is the key to growing potted citrus trees successfully. The soil should be kept moist, not wet. Water only when the top 2 inches (5cm) of soil is moderately dry. When you do water, may sure it is thorough. The water should drain into the saucer and emptied. During hot weather, you may have to water once or twice a day. During cool weather, water sparingly.
Water quality is an important thing to consider when growing citrus. If your tap water is hard (alkaline), it will cause certain elements in your soil to become unavailable to the plant. Add a tablespoon of vinegar to 1 gallon of water to lower pH.


Fertilizing
No citrus tree, whether in a container or in the ground, can grow and produce well without an adequate fertilizer program. Citrus trees are heavy feeders. Use a balanced fertilizer that contains high nitrogen and moderate amounts of phosphorus and potassium (example: 12-4-4, 21-7-7). It should also contain trace minerals (iron, copper, zinc, manganese, etc) in chelated form for better absorption. Apply fertilizer during spring and summer and feed lightly during fall and winter.
If you're into organic gardening, I recommend blood meal for nitrogen, bone meal for phosphorus, and sulpomag for potassium and magnesium. Greensand is also good for iron, potassium, and many trace elements. Liquid kelp or kelp meal is excellent for improving the soil and supplying trace elements.
Do not use any products that contains alfalfa meal or cottonseed meal. Anthracnose is known to attack alfalfa and cotton, and there is a strong possibility that you can introduce your plants to this fungal disease which causes leaf spots.


Light
Having adequate light indoors is absolutely essential for good growth and fruiting. Citrus trees require a minimum of 5 hours of direct sunlight, though 10 to 12 hours is ideal. Supplementary lighting can be used to make up the difference. There are many different lighting systems available. HID lighting, T5 High Output, and the newer T5 Very High Output lighting offer the best quality light for successful flowering and fruiting of citruses. More information about lighting systems can be accessed at myindoorgreenspot.com menu page under houseplants.


Temperature/Humidity
Citrus trees require a warm, frost-free environment to grow and produce well. They can withstand temperatures over 100F (37.5C), however, growth is sharply reduced below 55F (13C). Indoor growers should provide a subtropical growing environment for their trees if possible. A temperature of 75 to 90F (24-32C) for spring and summer is ideal. During the fall and winter, a temperature range of 60 to 70F (16-21C ) is ideal. In either case, the low temperature should not go below 45F (7C).
Some citrus trees are more cold tolerant than others. Container grown trees are less cold hardy than trees grown in the ground. As a general rule, potted trees shouldn't stay outside below 50F (10C). The most to least hardy citruses are: trifoliate orange, kumquat, mandarin, sour orange, sweet orange, pummelo, grapefruit, lemon, lime, and citron.
The indoor relative humidity should be in the 45% to 50% range during the heating season. A room humidifier should be used to maintain humidity levels and a hygrometer should be used to monitor it.


Acclimating Citrus
When you are ready to move your citrus tree indoors for the winter or outdoors for the summer, it needs to be acclimated to its new environment to avoid a severe shock. The indoor/outdoor temperature should be as close as possible for the transition move. Before moving citrus indoors, it should gradually be shaded over a period of 3 weeks. When tree is moved outdoors, place it under a shade cloth, a lath shade structure, or in an area that receives only the weak morning or evening sun. Over a period of 3 weeks, gradually introduce to more sunlight. After the tree has been properly acclimated, place it in a sunny, southern location sheltered from strong winds. The ideal spot is one that receives sunlight from sunrise to sunset. Before the permanent move outdoors, the temperature should be moderately warm and consistent over a 2 to 3 week period.


Growing Sweet Citrus
It takes resourcefulness and patience to grow sweet citrus in a cold climate, but it can be done quite successfully. Choosing the right variety is an absolute must! Citrus varieties that grow and produce well in the mild coastal regions of California are ideal candidates for indoor citriculture.
Sweet citrus demands a lot from its environment in terms of heat required for growth and ripe fruit. Since a long growing season is required for optimum growth and performance, a greenhouse is needed to provide extra growing heat. A simple greenhouse can be made out of a 4 foot (1.2 meters) tall wire fence-the kind used to make tomato cages. Stake the cage and wrap it with clear plastic. It should be adequately ventilated to prevent overheating, and the pot should be shaded to keep roots cool and reduce water needs. Greenhouse


Sweet Citrus Varieties
I recommend the following varieties for advanced indoor citrus growers who enjoy a challenge. I selected these varieties based on their heat requirements: 75F to 90F (24C to 32C), fruit quality, and adaptability. All varieties are available on dwarfing rootstock.
Valencia Orange
This variety is the standard among juice oranges in the world. It is widely adaptable from cool coastal to hot desert areas. The tree has a vigorous growth habit, and the fruit is medium-large, very juicy, sweet, with few or no seeds. It takes 14 to 18 months to ripen with an orange or greenish-orange rind. Mature fruit can be held on the tree for a few months.
Washington Navel Orange
This variety is the standard among fresh eating oranges. The tree is moderately vigorous, productive, and sensitive to changes in temperature. The fruit is large, richly flavored, sweet, juicy, and seedless. It takes 10 to 13 months to ripen with a deep orange rind. Mature fruit holds on tree a few weeks after ripening. Best grown in a cool greenhouse. Highly recommended for its fruit.
Trovita Orange
This California orange variety is definitely worth mentioning. I have experience growing this variety, and it makes an excellent houseplant. The tree is vigorous and productive! The fruit is medium-large, sweet, and juicy with an excellent orange flavor. It takes 12 to 14 months to ripen with an orange rind. Mature fruit holds on tree a few weeks. Highly recommended for its adaptability and fruit.
Owari Satsuma Mandarin
The tree is slow growing, very cold tolerant, and capable of tolerating unfavorable conditions. The fruit is medium-small, seedless, juicy with a mild, sweet flavor. It ripens in 10 months with a bright orange rind. Mature fruit holds on tree about a week before deteriorating on tree, however, it stores well in the refrigerator. Highly recommended for its tolerance to adverse conditions and fruit.
Kinnow Mandarin
The tree is vigorous and productive with an upright growth habit. When I tasted the fruit from this tree, it was richly-flavored, very juicy, seedy, and sweet! The fruit ripens in 12 to 15 months with a yellow-orange rind. Mature fruit holds on tree a few weeks. Best grown in a cool greenhouse. Highly recommended for its fruit.
Clementine Mandarin
The tree is slow growing with an attractive weeping habit. The fruit is about 2 inches in diameter, juicy, and sweet with few or no seeds. Fruit ripens in 9 to 12 months with a bright orange rind. Mature fruit holds on tree a few weeks.
Oroblanco Grapefruit
This patented, white-fleshed grapefruit variety is actually a cross between a grapefruit and a pummelo. I have tasted the fruit, and it is superb! The fruit is large, very juicy, seedless, pleasantly flavored, low acid, and sweet like an orange. It ripens in 10 to 13 months with a pale yellow, thick rind. Mature fruit doesn't hold well on tree. Highly recommended for its fruit.
Moro Blood Orange
The tree is very productive and nearly thornless. The fruit is small to medium size, juicy, sweet, rich, with an exotic flavor. Flesh color is a deep red at maturity. Fruit ripens in 12 to 15 months with a reddish-orange rind. Best grown in a cool greenhouse.


Growth Habit
Citruses make beautiful evergreen trees. They grow with an upright, spreading, or weeping habit and some have thorns adjacent to the leaf axils. They have 4 to 5 growth cycles or flushes a year and root growth tends to alternate with top growth. Trees grow most vigorously when it is warm and humid. They go into a dormant-like state when the temperature is around 55F (13C) or when there isn't enough water available for growth.


Flowering and Fruiting
Most citrus varieties are self-pollinating, however, a few do require cross pollination from another variety. Under indoor cultivation, citrus trees tend to bloom somewhat on a regular basis. A winter rest period is recommended especially for fruit bearing sweet citrus trees. Vigorous growth and flowering during the winter will divert energy away from developing fruits. To rest trees cut back on fertilizer and watering and/or lower room temperature.


Pruning
Citrus trees store their food in their leaves; therefore, the amount of leaves removed will have a direct impact on the tree's fruit-bearing capacity. Prune only to remove dead, broken, diseased, or crossed branches. Remove all growth coming from below the graft union. For size containment, use thinning to control desired height and spread. Use heading to fill in gaps within the tree.


Rootpruning
Potted citrus trees can thrive for many years if they are rootpruned regularly. Only new roots are able absorb water and needed elements. Roots that are pruned respond in very much the same way as branches do when they are pruned. Without rootpruning, trees will stagnate. Fertilizer will not help! Here are some rootpruning guidelines:
  • Faster growing citruses, like lemons, require more root maintenance than slower growing trees.
  • Prune about 1/3 of the foliage to counterbalance roots removed.
  • Never rootprune an actively growing plant. Wait until the tree shows no sign of growth. If you're going to prune your tree outdoors, do it in the shade and wait until the weather is cool.
  • Don't allow exposed roots to dry out. Keep a spray bottle handy.
  • Remove large, circling roots with a clean pair of pruning shears. After that, take a sharp, clean knife and shave to 1" around the rootball. Repot immediately and water.
  • If you're repotting your tree to the same pot, replenish as much as the old soil as possible. Use the same type of potting mix it was growing in.


Propagation
Citrus can be propagated by seeds or leaf cuttings. It's fun to watch a seed sprout and develop, through care and training, into an attractive evergreen tree. Take seeds from a fruit and rinse them removing the adhering flesh. Plant seeds in a small pot with a professional soil mix. They should be planted an inch deep. Keep the pot in a warm, bright location. Don't let the soil dry out. About 3 to 4 weeks later, there should be signs of growth.
Propagating citrus from a cutting insures varietial integrity. Take a four inch cutting from a recently matured growth flush. Cut just below a leaf bud and remove half the leaves. Dip cutting in a rooting hormone solution and plant in a sterile rooting medium. Keep soil moist and humidity high and cutting will root in about 4 weeks. Bottom heat is recommended. If you take a cutting from a dwarf tree, it will not develop into a dwarf. Dwarfing occurs if you graft a selected variety onto a dwarfing rootstock.


Grafting
If you want to grow two or more citrus varieties on one tree, then grafting is your answer. The simpliest grafting technique is T- budding. Check out grafting techniques at your local cooperative extension office or horticultural websites.


Pests and Diseases
Indoor citrus growers have far fewer pests and diseases to deal with than commercial citrus growers. Spider mites, aphids, mealybugs, and scales do occasionally attack citrus while indoors and outdoors. For small infestations, use a spray bottle filled with mild, soapy water. Thoroughly wash down tree and repeat once a week. For medium to heavy infestations, use neem oil solution.
Indoor citrus growers need to create their own pest management program. As a start, check the leaves, especially the undersides, at least once a week. Any new plant arrival should be quarantined and monitored for pests.
Diseases that show up on indoor citruses are sometimes due to incorrect cultural practices. Overwatering can lead to root rot. Fungal leaf problems can develop when leaves stay wet without adequate air circulation to dry them quickly.


Troubleshooting Potted Citrus Trees
Symptoms Probable Causes Solutions
Leaves change color and drop, flower buds drop Too much light or not enough, underwatering, overwatering, low humidity, sudden temperature change Gradually move plant to brighter location, water only when the top 2" (5cm) of soil is moderately dry, increase humidity, keep growing environment stable
Leaves turn pale with green veins Interveinal chlorosis caused by a micronutrient deficiency Use fertilizers that contain chelated trace elements
Fruit drops off before maturing Low humidity, water stress, sudden temperature change, natural thinning of fruit Buy a humidifier to increase humidity, water soil thoroughly especially during warm temperature.
Leaves pucker, distort, or turn pale before dropping Environmental shock, insect infestation Keep environmental conditions stable, check for insects on leaves and stems with a magnifying glass.
No flowers on healthy plant Plant was grown from seed, not of fruit-bearing age, a rootstock sucker has taken over, pruning reduces fruitfulness Seed grown plants can be unpreditable, grafted dwarf trees take 2 to 3 years to start bearing fruit, prune lightly
Fruit doesn't ripen Inadequate heat Increase temperature
Leaf veins turn a lighter color than surrounding tissue followed by a slow bleaching away of green over the entire leaf to a mottled irregular green and yellow pattern. Eventually the entire leaf turns yellow and drop. Vein chlorosis caused by a nitrogen deficiency, cramped roots, or root rot Use a high nitrogen fertilizer, check rootball
Leaves start to fade in color, develop spots, and eventually drop. New growth becomes stunted. Leaf spot disease Cool temps combined with water sprayed on leaves will rapidly spread disease. Use copper fungicide soap or 70% neem oil.


Harvesting
The ultimate goal of growing citrus trees is to enjoy the fruits of your labor. Knowing when to harvest can be difficult. Here are some facts to help determine when the best time to pick.
  • Generally speaking, acid citrus fruits take 7 to 9 months to ripen and sweet citrus fruits take about 12 to 18 months to ripen depending upon growing conditions.
  • Know the variety of citrus you are growing and what the size, shape, and color of the fruit should be when ripe.
  • Know the season in which the fruit is harvested. Does the fruit ripen in the fall or winter, or does it ripen in the following spring or summer?
  • Keep fruit on tree as long as possible because once harvested it will not improve in quality.
  • Sampling the fruit to determine sweet ripeness is a foolproof method.


Nursery Links
Four Winds Growers
Box 3538, Mission San Jose District
Fremont, CA 94539
http://www.fourwindsgrowers.com
This citrus nursery offers a wide selection citrus varieties on dwarfing rootstock.
Edible Landscaping
P.O. Box 77
Afton, Virginia 22920
http://www.eat-it.com
This nursery has an assortment of decidious and subtropical fruit trees. It offers a few citrus varieties on dwarfing rootstock.
Raintree Nursery
391 Butts Road
Morton, Washington 98356
http://www.raintreenursery.com
This nursery has an assortment of decidious fruit trees. It offers a limited selection of dwarf citrus.



Last Updated November 19, 2011
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