Citrus Cultural Practices

Here are two articles on citrus cultural practices from knowledgeable UC Master Gardeners. The first, by Charles Davis, focuses on citrus history and Southern California-specific advice. The second, by Thorv Hessellund, offers practical, step-by-step tips for home gardeners?s. 

Citrus Cultural Practices

By Charles Davis, UC Master Gardener

Introduction

1. Worldwide, more fruit is produced by citrus trees than all other deciduous fruit trees COMBINED.
2. Citrus trees can be purchased on standard, semi-dwarf and dwarf rootstocks. All fruit on all three types of trees is standard size.
3. Citrus can be planted in pots, as espaliers against a fence or a wall, or as regular trees in the ground.
4. Citrus trees are believed to have originated in China; none of the trees grown here today originated in the New World. Introduced in CA by Spanish missionaries in 1769, by 1869 their future was in jeopardy due to the cottony cushion scale, a citrus pest, which threatened to destroy all of CA’s citrus trees.  In what was CA’s first spectacular biological control success story, the scale was conquered by the introduction from Australia of a natural predator, the Vedalia beetle, a cousin of the common   ladybird beetle.

Citrus Growth and Development

1. In contrast to deciduous trees, citrus leaves, along with twigs, branches and roots, store all excess food: the maximum amount is present in late February/early March just before spring bloom and new growth.  Do not prune at this time.  Pruning of mature citrus is often limited to removing dead, diseased or broken branches and is best done in late spring and early summer.  Lisbon lemons are the exception - this tree needs pruning or it will become unmanageable.
2. If pruning is needed, the top wood is the first to decline in production and fruit quality as trees age. The skirt or lower section is the most productive and pruning should be light.
3. Fall pruning produces a new flush of growth which is susceptible to frost injury.
4. Citrus fruit never needs to be thinned - excess fruit is dropped naturally: less than 5% of blossoms produce mature fruit.
5. First 3-4 years after planting are considered the nonbearing years. After which, the tree has several growth flushes producing flowers and fruit in the spring, summer and fall.  The biggest flush occurs in the spring.
6. Citrus does best in sandy-clay loam soil, in a wind-free location, and full sun near a south-facing wall. Wind can increase heat loss.
7. Don’t plant near plants with aggressive root systems. If in a lawn, remove turf in a 3-5’ circle around tree.
8. Never allow the root system to completely dry out. The most important irrigation period is from initial growth flush until fruit are at least 1 inch in diameter. Do not allow irrigation water to touch the base of the tree trunk, which encourages crown and root rot.
9. Young citrus are particularly vulnerable to frost conditions.
10. Lemon trees are particularly sensitive to sunburn.
11. Fertilizing: primary nutrient needed is nitrogen, required for flowering and fruit set - apply in late winter/early spring.  Oranges and grapefruit are susceptible to thicker rinds and less juice with high nitrogen if fertilized in the summer; lemons, however, benefit from it.
12. In our demo garden: Irrigation is applied two hours a day/twice a week with a 2 gallon emitter for each tree. Fertilization - we do not fertilize due to the drought and our desire to keep leaf growth to a minimum.  When we did fertilize, it was twice a year: at the end of January and the end of May.  Any balanced fertilizer will work, but for citrus the most important nutrient is nitrogen.

Southern California Climate Zone

1. Best type of citrus to buy (harvest periods in parentheses): Oranges: Washington - eating (Jan-May) and Valencia - juice (Apr-Oct); Lemons: Eureka (Feb-Sep), Lisbon (Jan-Aug) and Improved Meyer (year-round); Grapefuit: Oroblanco (Jan-Apr) - doesn’t require heat to sweeten; Limes: Bearss (Aug-May) - does not require high heat to ripen, be careful of Mexican or Key Lime (Jul-Dec) - high heat requirement and almost no tolerance to frost; Mandarins: Many varieties, Satsuma (Dec-Apr) are the most cold hardy citrus.
2. Heat requirements—lemons and limes need the least
3. Rootstocks: Four main rootstocks - Troyer and Carrizo Citranges; Trifoliate Orange; Flying Dragon Trifoliate Orange (dwarfing); Alemow.  All influence fruit productivity, size, and quality; overall tree vigor, resistance to fungal diseases, and cold-hardiness.  65% of rootstocks produced between 1950-1970 were Troyer.  Nurseries are not required to tell you rootstock variety.

Pests

1. California Red Scale - round red-brown scales on fruit, leaves and twigs: causes twig dieback and yellow leaves; most visible in late summer/early fall.  Use insecticidal soap or strong spray from hose.
2. Aphids – cause distorted, curled leaves, honeydew and sooty mold. Dislodge with strong spray or insecticidal soap.
3. Cottony cushion scale – look for fruit and leaves covered with honeydew and sooty mold; cottony secretion on scales and twigs. Hand remove, dislodge with strong spray or insecticidal soap.
4. Citrus thrips – cause ring or partial ring of scarred tissue on fruit rind near stem end; young leaves will be deformed and scarred. Damage is cosmetic; no treatment recommended for home gardens.
5. Argentine ants - harvest honeydew from aphids, scales, mealybugs and protect them from predators. Cut tree skirt up off ground; wrap trunk with green tape and spread Tanglefoot on top of tape.
6. Garden snails - holes in leaves and fruit; slimy trails. Skirt prune, apply copper tape, or hand pick.
7. The most serious threat to California citrus trees is the Asian citrus psyllid (ACP) as it can spread the deadly disease huanglongbing (HLB). Homeowners are asked to regularly check their trees for signs of ACP.  This insect is small, about the size of an aphid, and prefers the tender new growth.  If you suspect you have ACP, call the CDFA hotline at 1-800-491-1899.  For more information and photos of ACP, visit http://ucanr.edu/sites/acp/

Conclusion

1. If you live south of the grade, citrus is well adapted to this county. If you live north of the grade, be very careful.  Citrus in pots is probably the best option.
2. Feed and irrigate properly and plant in right location to avoid problems.
3. Check trees regularly for pests and take appropriate action before they’re a problem.
4. Choose a variety well-suited to your location.
5. Citrus are not difficult to manage, most need minimal pruning, no fruit thinning and can be adapted to small spaces (pots or espaliering).

References

"Edible Plants." - UCCE Master Gardeners of Orange County, CA. Edible Plants - UC Master Gardeners of Orange County

Lazaneo, Vincent. 2016. Citrus For The Home Garden. Ebook. 1st ed. Cooperative Extension, University of California, County of San Diego. citrus for home garden.pdf

Mauk, Peggy, and Tom Shea. 2016. Questions And Answers To Citrus Management. Ebook. 3rd ed. Moreno Valley: University of California Cooperative Extension. Microsoft Word - Citrus Management Questions-3rd edition.doc

Pittenger, Dennis R. 2015. California Master Gardener Handbook. 2^nd ed. Oakland, CA: University of California, Agriculture and Natural Resources Communication Services.

Tagliareni, Marilyn. 2007. Citrus For The Home Garden In Contra Costa County. Ebook. 1st ed. untitled

Citrus Cultural Practices

By Thorv Hessellund, UC Master Gardener

Citrus trees can be a wonderful part of a home garden, with evergreen foliage, pretty flowers and colorful, nutritious fruit.  The purpose of this care guide is to provide an outline of cultural practices which will facilitate successful growth of these trees in your yard.

Planting

The best time to plant citrus is after the danger of frost is over and before the onset of hot weather.  For optimal fruit production, choose a location with full sun throughout the day, protected from the wind and preferably south or west facing exposure.  Planting in a lawn is not recommended.  The planting hole should be the same depth as the root ball and at least twice the diameter.  Adjust the depth of the hole so the surface of root ball or container soil is one inch above the surrounding ground.  Manure or fertilizer should not be placed in planting holes as it can injure the roots.  Amended soil is not recommended unless there are extreme conditions such as heavy adobe clay.  Water immediately; do not let root ball dry out or get soggy.  To protect young trees from sunburn, paint the trunk with white indoor latex paint diluted with an equal amount of water.

Irrigation

Proper water management is the most important factor in establishing a new tree and keeping a mature tree healthy.  The soil should be kept moist, but not soggy.  An irrigation schedule is determined by the age of the tree, soil type and weather.  New trees need to be irrigated every 3 to 7 days, depending on soil type and weather.  More frequent irrigation is needed with sandy soils or hot weather, and less frequently with clay soil or cool weather.  Don’t let the root ball of a new tree dry out, and place emitters near but not adjacent to the trunk, one on each side.  If emitters are spray type, direct spray outward and do not wet the trunk.  After the first year, move the emitters away from the trunk, water a larger area around the tree as it grows and irrigate every 10 to 14 days.  One of more common mistakes in citrus tree care is over watering which results in waterlogged roots that cannot function properly.  Overwatering is one of the causes of yellow citrus leaves.  A soil moisture probe can be very helpful to help gauge soil moisture and time the irrigation for your soil type and weather conditions.  If the top inch of soil is dry, don’t water, but if the top several inches of soil are dry, water.  Keeping the soil moist to a depth of two feet is best.  It is not recommended to place a citrus tree on automatic watering timer with other plants that have different irrigation requirements.

Fertilization

Young non-bearing trees in the first two years have different nutrient needs than mature trees.  Nitrogen is the main nutrient that needs to be supplied, usually in the form of ammonium sulfate, ammonium nitrate or urea.  The general recommendations are: for one to two-year-old trees, 2 tablespoons of nitrogen fertilizer spread under a tree three to four times a year from early spring through late summer, prior to irrigation.  The amount of nitrogen fertilizer is increased to 4-5 tablespoons for three-year-old trees, and 8 tablespoons for four-year-old trees applied three to four times a year.  Mature fruit bearing trees will need from one and half to 3 pounds of fertilizer per year divided over three to four applications.  Most gardeners fertilize trees between February and August, in 3 to 4 evenly divided applications. Nitrogen fertilizer should not be applied after late summer, as this promotes new growth which is susceptible to frost injury and citrus leafminer damage. Some arborists recommend not fertilizing oranges and grapefruits during summer months as this may contribute to thick rinds.  If this is a concern, a single application of the yearly fertilizer requirements can be applied in late December to February.  Lemons, however, do well with summer fertilization. As trees mature, transition to a slow-release fertilizer formulated for citrus- always read the label and follow manufacturer’s instructions.  In addition, mature trees may benefit from micronutrient sprays or chelated iron to prevent various patterns of leaf yellowing.

Pruning

Citrus trees need little to no pruning in first 2 to 3 years.  In young trees, pruning is limited to removal of suckers which arise below the graft union and trimming of vigorous shoots in order to maintain overall canopy balance.  For mature trees, pruning can be done in late spring to summer to remove dead, damaged, diseased, crossing or weak branches.  Prune the lower branches off the ground to eliminate as easy access point for ants.  It is not necessary to use pruning sealants on pruning wounds.  Wait until May to remove any frost damaged wood.

Mulching

Apply mulch in a two-inch-thick layer matching the circumference of the tree canopy, but 6 inches from the trunk.  Mulch reduces weeds and eliminates the need for cultivation around shallow citrus tree roots.  It conserves water, improves soil conditions, reduces soil temperature fluctuations and prevents root rot fungi.  Yard waste such as wood chips, leaves, and grass clippings provide excellent citrus mulch.  As an added benefit, organic mulches such as alfalfa straw can reduce ground water nitrate contamination by providing a continuous but slow release of nitrogen.

Pests and Diseases

Good cultural care is the primary defense against pest and disease problems. Whitefly and leafminer are the primary pests of citrus in our county.  Aphids, scale, mealybugs, slugs and snails can also be a problem.  Citrus leafminer usually needs no treatment except to discourage vigorous new leaf growth during the leafminer’s peak lifecycle.  Leafminer is typically most abundant when citrus is flushing in the summer and fall.  Scale insects are most sensitive to pesticide treatment during their crawler stage, from spring to late summer.  The most important action a homeowner can take to prevent honeydew producing pests - such as aphids, scale, mealybug and whiteflies - is ant control.  Check trees regularly for ants climbing up the tree trunk. Ants feed on the honeydew and they protect the pests from beneficial insect predators.  Control ants by trimming branches off the ground and applying Tanglefoot on the tree trunk. The most serious threat to California citrus trees is the Asian citrus psyllid (ACP).  ACP can spread the deadly disease huanglongbing (HLB). There is no cure for the disease; therefore, the best line of defense is to manage the psyllid.  Homeowners are asked to regularly check their trees for signs of this ACP. This insect is small, about the size of an aphid, and prefers the tender new growth. If you suspect you have ACP, call the CDFA hotline at 1-800-491-1899.  For more information and photos of ACP, visit http://ucanr.edu/sites/acp/

References

"Edible Plants." - UCCE Master Gardeners of Orange County, CA. Edible Plants - UC Master Gardeners of Orange County

Lazaneo, Vincent. 2016. Citrus For The Home Garden. Ebook. 1st ed. Cooperative Extension, University of California, County of San Diego. citrus for home garden.pdf

Mauk, Peggy, and Tom Shea. 2016. Questions And Answers To Citrus Management. Ebook. 3rd ed. Moreno Valley: University of California Cooperative Extension. Microsoft Word - Citrus Management Questions-3rd edition.doc

Pittenger, Dennis R. 2015. California Master Gardener Handbook. 2^nd ed. Oakland, CA: University of California, Agriculture and Natural Resources Communication Services.

Tagliareni, Marilyn. 2007. Citrus For The Home Garden In Contra Costa County. Ebook. 1st ed. untitled