CULTIVATION, STORAGE & PACKAGING

Preharvest:
Lemon trees grow from 10 to 20 feet in height with sharp thorny branches. Flowers are single or bunched two or more together in leaf axils. Less than 1% of pollinated buds will produce fruit. Trees usually achieve full fruit production by the eighth year of growth.

Lemon trees are less sensitive to cold than lime trees, but since they both grow continuously, they are more susceptible to cold damage than orange trees and less capable of recovery. Climate is more limited for lemons than for other citrus as trees produce the best fruit in coastal areas with cooler summer temperatures, but cold snaps can be devastating. Lemon trees can thrive in either humid or dry conditions and tolerate rainfall between 25 and 125 cm per year although irrigation is necessary for drought conditions.

Temperatures below 29°F will kill flowers and new fruit and just one degree colder can severely damage mature fruit. The 24 to 22°F temperature range will defoliate the tree, while below 20°F can damage wood.

Many different types of soil are acceptable, which can even grow on sand or silty clay loam, but pH levels should be between 5.5 and 6.5. Rough lemons can be grown from seed, though Meyer lemons are generally grown via rooting cuttings for transplant. Trees should be placed 25 feet apart each way and must be protected from wind, which will scar both fruit and tree.

Postharvest:
Lemons are hand-picked at different stages for varying marketability. California and Arizona producers pick lemons any time after they have attained 25% juice content. Some, such as Italian lemons, are picked early and cured. Others are harvested at maturity.

Fruit is packed into bins in the field and transported to packinghouses for cleaning, grading, sizing and final packing. Lemons are coated with a fungicide and thin wax layer before curing in storage and later shipping. Some growers cure loose fruit before moving on to the grading stage and another round of curing. Early-picked lemons require about three weeks to attain best color but green lemons may be kept for four months or longer. More mature lemons may need less than a week to cure.

Degreening can be expedited by exposure to ethylene gas, ethephon, or silane, but care must be taken as this can also promote decay. Packing lemons in 10 micrometer-thick, high-density polyethylene may minimize decay and allow storage for up to six months. Lemons can generally be kept for up to six months between 54 and 57°F with 90 to 95% relative humidity.

Tree yield varies by cultivar and location and is usually measured in 900-pound field bins per acre. Lemons are sold in packed 40-pound cartons and a 900-pound bin consists of 23 or 24 cartons. Lemons exported from Florida to Hawaii and Arizona are fumigated with methyl bromide to prevent Caribbean fruit fly infestations.

References: Agricultural Marketing Resource Center, Purdue University, UC Davis Postharvest Technology website, University of California Cooperative Extension.

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