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Growing Grapefruit: Citrus paradisi

Botanical Overview

Members of the Citrus family (Rutaceae), modern Citrus fruits, according to genetic analysis, are complex hybrids arising from mandarin, pomelo, and citron ancestors, refined by more than four thousand years of cultivation. Grapefruit was first identified in Barbados, and resulted from an accidental cross between Sweet Orange and Pomelo. Many cultivars are now available.

Description

Form: Tree.
Lifespan: 50-150 years, with the first 35-50 being the most productive.
Leaf retention: Evergreen.
Growth rate: Moderate.
Mature Size: To 30' high and 25' wide without a dwarfing rootstock.
Flowers: White, four petals, fragrant.
Bloom: Winter.
Self-fruitful: All cultivars self-pollinate.
Years before fruiting: 3 for grafted trees, 10 for those grown from seed.
Fruit: Round to oval, a thick yellow rind, with flesh that can be white, pink or red, aromatic, and slightly bitter. The red fleshed cultivars tend to be sweeter.
Months for fruit to ripen: 10. Grapefruit may be allowed to stay on the tree after ripening until May.
Storage after harvest: Up to one week at room temperature or several weeks refrigerated.
Leaves: Glossy dark green, lance-shaped, smooth margins.
Stems: There are short thorns on the twigs. The bark is prone to sunscald if not shaded by the leaves, especially in higher temperatures.
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:
'Rio Red' - Sweet red flesh, few seeds.
'Oro Blanco' - Sweet yellow flesh, few seeds, easy to peel, a hybrid of grapefruit and pomelo.
Wildlife: The flowers attract bees and other pollinating insects. The fruit attracts birds. Mammals may strip the bark off of young trees, consume fallen fruit, or climb the tree to eat the fruit. The leaves are a food source for the Giant Swallowtail butterfly caterpillar – see Pests, below.
Toxic / Danger: Possible thorns. Grapefruit can interact with many medications, including chemotherapy, making them more, or less, effective and throwing off the prescribed dose.
Origin: A natural hybrid first recognized in Barbados.

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Cultivation and Uses

USDA hardiness zones: 9-11. Somewhat less cold-hardy than oranges.
Chill hours: None.
Heat tolerant: Yes.
Drought tolerant: Depends on the rootstock. Drought will damage the fruit 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.
Soil: Well drained 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: Dropped fruit must be picked up immediately to avoid attracting wild animals.
Propagation: Cuttings grafted onto disease resistant rootstock adapted to the local climate. Trees grown from seed are usually true to their parent tree characteristics.
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: Ornamental, edible fruit.

Comments

The fruit and flowers pictured are 'Oro Blanco'.



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Grapefruit: Citrus paradisi - flowers and fruit



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Latest update: October, 2020