Citrus Trees

By Annette Truong

Love Apple Farms

Agenda

• 9-10 Lecture

• 10-10:30 Planting outside

• 10:30-11 Tasting

• 11-12 Budding

Background

• Volunteering at Gene Lester’s citrus orchard for 1.5 years.

• Gene grows over 200 varieties of citrus and provides his citrus to Manresa restaurant

Citrus Basics

For Northern California

Classification (Wikipedia)

• Citrus is a common term and genus (Citrus) of flowering plants in the rue family, Rutaceae. Citrus is believed to have originated in the part of Southeast Asia bordered by Northeastern India, Myanmar (Burma) and the Yunnan province of China

Characteristics

• Citrus trees are evergreen. The leaves look like those of deciduous trees but they don’t fall off in the same way and the tree doesn’t go dormant.

Thorns!

• Citrus trees are thorny!

• Australian citrus have smaller leaves and more bristly thorns

Fruiting times

• They bear fruit all year long, favoring late winter

• I don’t really understand charts like this: most orange trees will have some ripe fruit present all year long

Climate• Citrus grow well in subtropical climates

• They can even grow in deserts (Arizona)

• Drought tolerant (similar needs to cactus)

• Somewhat cold tolerant (can withstand some freezing)

Fruit variability by location• Variability among flavor and other fruit

characteristics varies widely by climate• The same tree will produce fruit that tastes

different if grown in hotter or colder regions.• San Jose vs Santa Cruz vs San Joaquin valley

– regional differences

Basic conditions

• In general, citrus are heat-loving

• Southern exposure, full sun

• Well drained (sandy) soil

• Soil pH: low (high acid) 6 or lower

Nutrition• Monthly feeding• Acid-loving fertilizer: 30-10-10

– Gene recommends “Miracid” but you can choose organic as long as it is high nitrogen

• Foliar as well as ground feeding

• Container-grown need special care with nutrition. Nitrogen deficiency is easy to get

Micronutrients

Probably in your soil

Potassium deficiency results in smaller fruit

There are a myriad of reasons why citrus leaves yellow!

Fertilizing (con’t)

• Container fertilizing– Much more important

than in-ground– The pot soil leeches

out more quickly– Once per month is ok,

just never forget (more important)

Soil pH & nutrition uptake

• Lowering the pH of your soil will help your tree’s nutrition uptake

• Acid loving - pH test your soil yourself

• Most soil in this area is neutral. • Sulfur, peat, iron sulfate will lower

pH• If your pH goes above 7 your tree

will yellow and look sickly

No Salt!

Citrus will NOT tolerate Boron or salty soil.

Temperature effects

Temperature vs Growth

• Growth happens above 55 degrees

• When the temperature drops below 55 consistently, you can stop fertilizing as the tree is not using it anyway

Cold Hardiness(most hardy)KumquatSatsumaSweet OrangeNavel OrangeMandarinGrapefruitTangerineTangeloLemonLime(least hardy)

Sustained <28 degrees will cause damage, any lower could kill the plant. Frost protection for may be needed (mulch & wrap).

Acid Level• Low temperature =

sour. – Favors fruit that is

attuned to high acid.

• Lemons from Florida will not have the same tangy sourness as those from Santa Barbara

Sugar Level

• Sugar level– High temperature == sweet.

Fruit will reach full sugar potential

– Grapefruit from Santa Barbara will not be as sweet as that grown in Florida

– Acid & Sugar in balance == high flavor– High acid / low sugar == sour flavor– High sugar / no acid == no flavor

…and there’s also bitterness– Grapefuits & pummelos will also not get very

sweet in our area– takes 14-16 months to sweeten up

• Bitterness vs. sourness: Not the same thing• bitter & sour == cold climates

– California grapefruit

• bitter & sweeter == hot climates – Florida grapefruit

Color of blood oranges

• Blood oranges don’t “color up” as well in cooler climates

• They color up extremely well at LindCove (UC Riverside)

• There is some combination of temperature and climate and ripening duration that needs to be met for coloration to occur

Thick Rinds

– Grapefruits and pummelos will develop a thicker rind in a cooler climate

– Night time temperatures, plus overall 24 hour temperature average

– Also phosphorus deficiency

Problems

Most CommonProblems

• Nutrition deficiencies

• Insect damage (mainly snails and aphids)

• Gopher damage (roots)

• Not enough drainage (root rot)

• Fungus, bacteria

• Temperature (too cold or hot)

• Severe drought• http://www.ipm.ucdavis.edu/PMG/C107/m107bpleaftwigdis.html

Macronutrient deficiencies

• Low Nitrogen = yellow leaves, pale & smooth fruit peel

• Low Phosphorus = hollow core, thicker rind

• Low Potassium = smaller fruit

Micronutrient deficiencies http://www.crec.ifas.ufl.edu/extension/greening/ndccg.shtml

Pollination

• For fruit set, pollination is required (bees or by hand)

• Self-pollination (same-variety) results in fewer seeds– Pollen grain from same plant variety– This is why orchards plant varieties in blocks– The middle of the block will be essentially seedless– Trees on the edges may have more seeds due to

external pollen sources brought in• Cross-pollination results in more seeds

– “Seedless” may become “seedy”– There is some leeway in the variety itself

Pruning

• Remove water sprouts• If shaping: remove no more

than a third of the tree in one year

• Keep the aprons! Citrus will naturally form globe-shaped trees with branches to the ground. Essential in hot climates

• Can be trained and pruned decoratively

Planting• Well-drained (sandy) soil

– Start with some kind of loamy loose soil (top soil). Mix in organic matter and sand

– For pots, just use potting soil

• Mound first with sandy soil on top of the existing elevation (18” high, 36” diameter), with a flat top on the top of the cone with a bit of a dish so the water doesn’t run out after the cone solidifies

Staking is not required

Irrigation• Drip irrigation makes watering easy

– 2-3 hours on mature trees, when the trees seem water stressed. Don’t let them wilt too much. Non-water stressed leaves are shiny and flat. When they start to get dull and curl a bit, they are water stressed.

– In the summer, one deep watering every 3-4 weeks

– New trees: every week or 2.

• Mulching– Use wood chips, a few inches deep– Shades the roots, helps retain moisture

End