Growing Citrus

Photo
The tree pictured on the right is a Meiwa Kumquat and has been in the ground for 3 years. It is planted on the East side of the house and therefore receives afternoon shade. Kumquats appear to suffer more from the AZ sun than other varieties of citrus because they are slow growing. Meiwa kumquat fruits are much sweeter and tastier than the more common Nagami kumquat. Meiwa fruit is also different than Nagami in its outward appearance being spherical in shape rather than oblong. Another kumquat, named Marumi, also has round fruit but they are smaller and spicier than the Meiwa. The Marumi tree has thorns whereas the Meiwa does not. Several Marumi trees are present on campus at Arizona State University. Meiwa kumquats are extremely hard if not impossible to find in Arizona nurseries. This is partly due to the fact that Meiwas are unusually hard to graft.

Overview
Citrus grow extremely well in the lower desert and in fact have been a commercial crop here for over 100 years. The most important aspect of growing healthy citrus is proper watering.

Fruit
Surprisingly, the weather in the Arizona desert produces some of the best tasting citrus in the world. Heat produces sugar in citrus fruits making them sweeter and cool weather produces acid making citrus more tart. The hot summers and cool winters in the desert therefore produce a much fuller flavored product than can be grown in either consistently warm climates such as Florida, or in consistently mild climates such as the California coast. California's desert regions produce comparable quality to that of Arizona. Another advantage that Arizona has over other regions is that citrus here can still be grown on Sour Orange root stock (see propagation section below for an explanation of root stocks), which produces some of the best tasting fruit. California and Florida have both had to ban Sour Orange because of its susceptibility to Tristeza, a citrus disease carried by a brown aphid. Fortunately, this aphid cannot survive the lower desert heat.

Citrus are categorized into the following major varieties. Within these major varieties are many cultivars. There are also some varieties that are hybrids of these varieties, such as Tangelos which are a cross between a mandarin (Tangerine) and a pummelo. The varieties below are arranged from least frost tolerant to most frost tolerant.

• Lemons and Limes
• Citrons
• Grapefruits and Pummelos
• Sweet and Sour Oranges
• Mandarins (includes Tangerines)
• Kumquats

Heat Tolerance and Sun Exposure
Citrus tolerate the summer sun well in Phoenix but will always get some sun burned leaves during the hottest weather. Varieties that grow vigorously manage to keep ahead of the sun burn better than varieties that grow more slowly. Kumquats and blood oranges suffer more from the sun than average for this reason.

The trunk and branches of citrus trees when subjected to direct sun can burn badly. In fact, if the trunk of a tree is fully exposed to sun it can kill it. Citrus naturally branch to ground and therefore protect their trunks. However, when a citrus tree is trimmed as a shade tree it exposes the trunk. This is the reason that trimmed up trees have their trunks painted white. Also, young trees should have their trunks wrapped until their branches provide shade. Furthermore, to hasten the establishment of newly planted trees the entire tree should be shaded from afternoon sun the first summer. Newly planted trees do not have a strong root system and can suffer substantially the first summer if subjected to all day sun.

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Cold Tolerance Freezing is generally not a concern in the lower desert unless one lives in an extreme microclimate, such as a low spot that collects cold air. Most citrus will not be damaged until temperatures are as low as the middle twenties Fahrenheit for several hours. Kumquats are the exception and can handle temperatures as low as 15 degrees F. In slightly cooler climates, such as Tucson, measures should be taken to protect citrus on the coolest nights. See the variety list above to learn how citrus varieties compare to one another for frost tolerance.

Planting
Dig a hole at least twice the size of the rootball. At a minimum, make the hole 2 feet in diameter and 2 feet deep. Back fill the whole with the dirt you removed, and maybe sort out any big rocks. Generally citrus do best without any added amendments during planting, even though some nurseries will recommend putting slow release fertilizer in the hole. It also is a good idea to finish with the hole an inch or two recessed so that a watering basin is formed. Citrus trees will establish more quickly if they are planted in a location that has good drainage, although I have found they will tolerate some fairly bad drainage if not overwatered. Caliche is the most common barrier to good drainage in the Phoenix area so this barrier should be penetrated where you plant your tree if possible. Many nurseries will offer to plant your tree for you for an extra fee. If they bring a jack hammer and break a hole through the caliche for you it is generally worth the money.

A tree will do best that is grown on rootstock suited to Arizona soils (see propagation section below for an explanation of root stocks). For this reason, plants grown locally are generally better than those imported from other states where rootstocks are chosen to suite a different type of soil. Sour Orange is the best rootstock for the lower desert.

The best time of year to plant a citrus tree is in late September. At that time the hottest part of the year is over and the tree will have the maximum amount of time to get established before next summer.

Watering frequency
Citrus trees do well on a citrus watering schedule. Proper watering is the most critical factor in the health of a citrus tree.

Watering method
Basin or flood irrigation is recommended because it helps keep the salt in our salty water from accumulating around the roots. Furthermore, deep watering will encourage the plant to develop deeper roots, making the plant tougher when the weather gets hot and dry.

Fertilizing and Growth Rate
Citrus are normally recommended to be fertilized three times a year for maximum growth in early March, late May, and middle September. Slower growing citrus need less fertilizer than more vigorous varieties. Newly planted trees should not be fertilized the first year because they are too easily burned. The recommendations on chemical citrus fertilizers bags are generally too high. To be safe one should half the rates recommended.

Slow release chemical fertilizers, and organic fertilizers such as fish emulsion can also be used, and are less likely to burn. Slow release fertilizer can be applied at the beginning of the growing season in March and once again in the middle of the growing season in early June, assuming it has an approximately 4 month release period. Organic fertilizers such as fish emulsion should be applied monthly during the growing season for maximum growth.

Any one of these fertilizers can be applied less often and at lower rates. A tree is very unlikely to starve to death. Trees can go for years without fertilizers and be relatively healthy as long as they are correctly watered. Fertilizers will just help a citrus tree grow better and produce more. On the other hand, over fertilizing a tree can cripple and kill a tree rather quickly.

I found that after my citrus trees are in the ground for many years, they eventually become chlorotic and growth slows. My theory is that they slowly use up all the Iron and Zinc within their root zone. I have used Liquinox Iron and Zinc diluted in a gallon of water and had fairly dramatic improvement when nothing else seemed to help.

Propagation
Citrus trees are typically propagated vegetatively by growing a select variety on top of a rootstock variety. There are two reasons for doing this. The first reason is that a tree grown from a seed will not produce fruit that tastes like that of its mother or father tree. It is possible that a seeds fruit could be superior to that of its parents but more than likely it will be inferior since select varieties are products of thousands of years of breeding. Also, a seedling tree would take much longer to start producing fruit. The second reason is that certain trees are better adapted to growing in certain types of soils.

For example, a sweet orange tree would grow poorly in Arizona soil. So, rather than grow a sweet orange tree directly in the soil a grower takes a sour orange variety, which does well in this soil, and attaches a sweet orange variety to the top of it. Since the lower part of the tree ends up being the roots it is called a "rootstock".

Rootstocks are not always content to stay as roots and will periodically attempt to grow branches. It is important to always prune off any rootstock branches that grow out below the graft line. If allowed to grow the rootstock will send branches into the canopy of the sweet orange tree and choke it out.

Pests
Citrus trees have no significant pests in Arizona.

Common Citrus Care Questions and Answers

Why are the leaves turning yellow?
This is usually caused by watering too frequently. Citrus do best when they are allowed to dry out between deep waterings. See above for a recommended watering schedule.

How can I tell when my citrus trees are thirsty?
When citrus trees are thirsty they noticeably droop and their leaves will start to curl. They will also do this somewhat during the hottest part of the day even if sufficiently watered, so it is most accurate to check them for hydration in the morning.

How can I tell the difference between fertilizer burn and sun burn?
Sun burn is most severe on parts of the tree that get the most sunshine and will occur on any part of a leaf. Fertilizer/salt burn starts at the tips of the leaves and will be more severe on the side of the tree that gets more sun, but will also be present on parts of the tree that receive less exposure.

I have leafhoppers on my tree. Should I poison them?
In Arizona leaf hoppers never seem to do significant damage. Furthermore, they are very stubborn and will be back on the tree in a matter of weeks after poisoning. Poisoning will also kill the leaf hoppers' insect predators so the insects you are trying to kill often come back even worse. Generally speaking, there are no citrus pests in Arizona that justify using pesticides.

How long after planting will a tree start producing fruit.
Citrus trees typically take 2 years after planting to start producing regardless of the size of the tree when planted. The amount of time is also dependant on the variety as well as how healthy the tree is.

Links to more citrus information

Greenfield Citrus