Growing Citrus on the Landscape
By Bob Chapman
Citrus can provide the California gardener with delicious, colorful fruits
envied 'round the world. Citrus will grow in any well-drained soil but
prefer a sunny location, such as a south-facing wall or a warm corner of the
yard. They thrive on regular, consistent feedings, deep watering and an
occasional hosing off of the dust on the leaves. Following the few simple
guidelines below will ensure success.
WATERING
It is said that over 50% of the problems with citrus are due to watering. It
is essential for citrus to have adequate moisture during the blossoming
period to alleviate problems with fruit setting.
* Water citrus when the soil six inches deep is barely moist. Then apply
enough water to soak the soil to a depth of 3-4 feet. Test by inserting a
thin probe. When the probe is easily inserted to 3-4 feet, you have applied
enough water. The best way to water citrus is by constructing a
doughnut-shaped basin to the outermost limits of the branches and a little
beyond. The edges of the basin should be 4-6 inches high. Leave a twelve
inch-wide mound of soil around the trunk to prevent collar rot, a serious
disease of citrus. After the rains stop in the spring, check the moisture
levels of the soil every 4-6 weeks or oftener. When the soil is barely moist
six inches deep, fill the basin with water and let it soak in.
* Citrus growing in lawns should be given an additional soaking two or three
times in the summer. Put a set sprinkler under the tree and let it run for a
couple hours to ensure water reaching the 3-4 foot depth.
FERTILIZING CITRUS
Citrus prefer a regular, almost continuous supply of nutrients. Many
gardeners use sulfate of ammonia, spread under the tree immediately before
watering, letting the water carry the plant food down to the roots. A mature
tree will require 3-5 pounds of sulfate of ammonia per year. Trees growing
in lawns or shrubbery borders should be fed when given the extra soaking in
the summer.
Citrus suffer from a lack of the micronutrients iron, manganese and zinc in
the soil. The leaves will tell you if there is a shortage of iron. If the
veins of the leaf are green, but the areas between are pale green or
yellowish, you can suspect an iron deficiency. If the leaf has discoloring
resembling a Christmas tree, suspect that a deficiency of manganese exists.
Correct these deficiencies by spraying the tree with a liquid fertilizer
(such as Miracle-Gro) containing these micronutrients when the leaves are
young, soft and not quite fully formed.
PRUNING
Do most of the pruning in summer, fall or winter.
* Oranges need little pruning, usually to cut off any deadwood inside the
tree. Oranges like to have branches all the way to the ground. This protects
the trunk from sunburn and brings fruit within easy reach. Do not let the
foliage touch the ground, however, as this provides an entrance point for
ants and snails.
* Lemons grow more vigorously, sending up strong, often wayward, shoots.
Unless needed to shape the tree these can be removed. Young suckers, those
not needed for a compact tree, can be simply rubbed off.
KEEP THE FOLIAGE CLEAN
Hosing cleans the leaves, washes off insect colonies, prevents dust (which
harbors mites), helps protect leaves from smog problems and allows natural
insect predators to protect your trees.
HARVESTING
Color can sometimes fool you. The best way to tell if the fruit is ready for
picking is by tasting it. Use pruning shears to cut off the fruit instead of
pulling it off. Harvest what you need, when you need it. Lemons and oranges
can be "stored" on the tree until needed. Oranges will keep this way for
several months after ripening. They lose a little of their sugars, but not
too much.
* "Sweetness" of the fruit
There is no way to increase the sugar content of citrus. Heat is the
governing factor. Citrus grown in coastal environments may never develop
enough sugar to match store-bought fruit. Most citrus, especially
grapefruit, need very hot summers in order to have sweet fruit the next
season. Lemons require the least amount of heat to ripen. If your oranges
aren't sweet, consider making juice from them, adding sugar to taste.
COMMON CITRUS PROBLEMS AND SUGGESTED CURES
-Chlorotic leaves. Yellowing leaves can be a symptom of a deficiency in one
or more micronutrients, iron, manganese or zinc, or poor drainage. To
correct nutrient imbalances, spray the tree with a liquid fertilizer
containing these micronutrients, such as Miracle-Gro, when the leaves are
young, soft, and not fully expanded.
-Insect pests. Hosing off the tree occasionally with a strong jet of water
will help control most insects bothering citrus. The trees natural predators
will help control invasions of aphids, whitefly, mealybug and scale. Ants,
however, "farm" these sucking insects, using excess exudate, called
"honeydew," as a food source. Keep ants out of the trees by banding the
trunk with masking tape and then covering this with Tanglefoot, following
directions on the container. Cut back any branches touching the ground, a
fence, building or other trees or shrubs that might serve as a "bridge",
allowing ants access to citrus trees. Sprinkling permethrin granules around
and under the tree will also help control ants. Severe infestations of
insects can be controlled with horticultural oil, insecticidal soap, or
malathion. Read and follow directions on the container for best results.
-No fruit setting. Excess dropping of small fruits or thin crop. Many
citrus bear heavily in alternate years. Thinning the fruit in the heavy
production years tells the tree to produce fruit the following season.
Citrus will undergo "self-thinning" when the fruits are about pea-sized. The
prodigious amount of flowers will set more fruit than the tree can handle
and it drops the excess. This condition is known as "June drop" and it often
happens during the first heat wave of the season.
-Holes in the leaves. Snails love citrus trees and may stay in a tree for
many weeks, eating merrily away. Prevent snails from climbing by placing a
copper collar around the trunk and by regular baiting or trapping.
-Fruit splitting. When winter rains coincide with the fruit ripening, there
may too much water absorbed, causing the fruit to swell and crack. Also,
cracking can occur if the tree is stressed from a lack of water and then
watered heavily. You can't control the rainfall but you can ensure regular
watering.
-Sooty Mold. This blackish stuff is a fungus that grows on the honeydew
excreted by insects. While not harming the leaves directly, it can prevent
light from reaching the leaf surface, causing the leaf to produce less food
and to turn yellowish. Prevent sooty mold by controlling the insects that
excrete the honeydew and preventing ants from accessing the tree. Sooty mold
can sometimes be hosed off or is washed off by winter rains.