Growing Lemons: Citrus limon

Botanical Overview

According to genetic analysis, Lemons, members of the Citrus family (Rutaceae) and Citrus genus, are complex hybrids arising from mandarin, pomelo, and citron ancestors, refined by thousands of years of cultivation. Citrus limon, the true Lemon, is widely grown commercially.

Description

Form: A shrub or small tree.

Lifespan: 50-100 years.

Leaf retention: Evergreen.

Growth rate: Moderate.

Mature Size: To 25' high and 20' wide without a dwarfing rootstock.

Flowers: White on top, five petals, fragrant.

Bloom: In mild winter regions, possibly all year.

Self-fruitful: All lemon cultivars self-pollinate.

Years before fruiting: On grafted rootstocks, 2-3 years. Discard any small fruits started in the first three years, which will probably be dropped before maturity anyway, so the plant can put more energy into growing roots and branches. A tree grown from seed will take 5-15 years to start fruit.

Fruit: Generally oval shaped, sometimes with pointed ends. When ripe, the skin is yellow and aromatic. The yellow flesh, very sour in the 'Lisbon' but slightly sweet in the 'Improved Meyer', may contain seeds or be seedless. The entire fruit is edible except for the seeds.

Months for fruit to ripen: 6-9. Lemons are ripe when their skin is entirely yellow. Their flavor does not ripen further after harvest, but they can be made to soften and finish becoming all yellow when picked early if the skin has some yellow. Place them in a window where they can receive direct sunlight. Early picked fruit ripened inside will not taste as good as one fully ripened on the tree, however. Do not allow lemons to remain on the tree more than two weeks when ripe, or they will become dry and tasteless.

Storage after harvest: Lemons last about a week at room temperature and four weeks sealed in a plastic bag in the refrigerator.

Leaves: Glossy dark green, broadly lance-shaped.

Stems: Twigs may have sharp thorns.

Roots: These trees are grafted onto rootstock that is used to control the height of the tree from dwarf, to semi-dwarf, to standard. The part of the tree above the graft, called the scion, is selected for its desirable fruit. The rootstock is from a hardier species which commonly has less tasty fruit.

Cultivars of Note:

'Lisbon' blooms in the spring, bears most of the year, has oblong fruit with a prominent nipple, is thorny, vigorous and productive, and being widely grown, is the standard commercial lemon.

'Eureka' blooms fall and spring, produces year-round, and has few seeds. Compared to 'Lisbon', it is slightly less cold-hardy and less thorny, less resistant to insect infestation and neglect, and shorter lived.

'Pink Variegated Eureka' has green and yellow striped fruit ripening to all yellow, pink flesh, blooms and fruits nearly year-round, has few seeds and variegated leaves, and is less vigorous than the typical 'Eureka'.

'Improved Meyer', a cross between two citrus cultivars, does not have the parentage of true lemon. It withstands a wider range of heat and cold, has a different flavor – sweeter and less acidic, bears year-round, has many seeds, but its thin rind has little lemon oil flavor, making the grated rind useless in recipes. It is often used to make lemonade.

'Ponderosa Lemon' is a hybrid of pomelo and citron, yet tastes like a lemon. It produces larger fruit with a thick, yellow, bumpy rind and many seeds. Possessing spiny branches that bear fruit throughout the year, it is less cold-hardy than 'Lisbon' and is often grown as an ornamental.

Wildlife: The flowers attract bees and other pollinating insects. The tree is a food plant for the Giant Swallowtail butterfly caterpillar – see Pests, below. Mammals may strip the bark off of young trees, consume fallen fruit, or climb the tree to eat the fruit.

Toxic / Danger: The fruit contain a family of chemical compounds called psoralens that are toxic to pets but not humans.

Origin: Asia.

Cultivation and Uses

USDA hardiness zones: 9b-11. Flowers and young fruit are damaged at 29°F, nearly mature fruit is damaged below 28°F, the plant defoliates at 22-24°F, and there is wood damage at 20°F. It needs protection from wind.

Chill hours: None.

Heat tolerant: Yes.

Drought tolerant: Depends on rootstock. Drought will damage the crop.

Sun: Full sun.

Planting: The best time to plant a citrus tree is after the danger of frost is past, in late winter or early spring.
Place the tree in a sunny location, away from the coldest part of the yard. Do not position the plant next to a frequently watered location, such as grass. Make sure there is enough space for the tree to grow to its full width and height, with clearance to walk around and where overhead lines will not be a problem.
Dig a hole twice as wide as the rootball, with the root crown at 1-2" above ground level. The top roots must extend out from the trunk, just above, and uncovered by, soil. The soil should slope gently downward from the trunk to the drip line.
Lemon trees can be grown in containers.

Soil: Well draining to prevent root rot. Do not amend the soil when planting. The roots will adjust to the native soil surrounding the planting hole.

Fertilize: Apply an organic fertilizer every month or two from mid-February to early October. Alkaline soils will cause iron deficiency. Apply a citrus micronutrient solution as necessary when leaves become yellow with green veins, signalling a micronutrient deficiency. Only use products containing iron in chelated iron form, which is more easily absorbed by the plant. Avoid chemical fertilizers because they increase salt build-up in the soil. Do not fertilize after September to keep the plant from producing new growth that will be harmed by early frost.

Water after becoming established: Basin irrigate or deep water for 1.5 hours or more until the water has reached a 3' depth. The frequency of irrigation depends on the species, the age of the tree and the month of the year. For trees in the ground three years or more, irrigate as follows: December-February, every 21-30 days; March-April, every 14-21 days; May-June, every 14 days; July-September, every 10-14 days; October-November, every 14-21 days.
Inward leaf curling, when the leaves are uniformly green, or drooping leaves, are signs of insufficient water. Solid yellow leaves are a sign of overwatering. Water near the drip line, not at the trunk.

Mulch: Apply organic mulch inside the drip line and 8" away from the trunk to reduce soil evaporation and reduce root zone heat and cold stress. Place a rodent gnaw guard around the trunk at the bottom.

Prune: Prune only after danger of the last frost is over in late winter or early spring. Flower buds develop during the winter dormant period, so pruning after the last frost makes it possible to avoid excess flower removal.
Citrus trees are best grown as shrubs, so that leafy branches protect their entire trunk from direct sun. Only prune the lowest branches if their tips touch the ground. If you prune up from the bottom to expose the trunk, you must paint it with a tree trunk paint to avoid sunscald.
Remove branches that are dead, damaged, diseased, or malformed. Remove any branches growing less than 45° from the vertical because they may split away as they get larger. Remove any new branches that have an angled cross section (malformed) rather than round. These have restricted veins and will not fruit well. Remove any branches growing from below the trunk graft as they occur. These are rootstock branches, not fruiting stock branches, and will produce inferior fruit.
Never prune to restrict the size of a citrus tree. Rootstocks are used to control the size of these trees.
Remove grass and other plants under the canopy that can compete for water and nutrients by hand-pulling, not with tools that can damage roots close to the surface.

Litter: Low.

Propagation: Cuttings grafted onto rootstock. Seed will not grow true and may be sterile.

Pests: Giant Swallowtail Butterfly caterpillar. This larvae resembles bird poop and has white and black and/or brown splotches. On a large plant it will cause no harm. On a small plant, relocate it to a large citrus.
Distorted leaf shapes are a sign of thrips, which do no real damage. Thrips are attracted to plants that are given too much nitrogen or are overwatered.
For other problems, see Citrus: Diseases and Disorders

Uses: Edible fruit, ornamental.

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