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.
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
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
- Grapefruits and Pummelos
- Sweet and Sour Oranges
- Mandarins (includes Tangerines)
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.
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.
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.
Citrus trees do well on a citrus watering schedule.
Proper watering is the most critical factor in the health of a citrus tree.
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.
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.
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