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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: 35-50 productive years.
Leaf retention: Evergreen.
Growth rate: Moderate.
Mature Size: 15-20' high and as wide.
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: Usually grafted onto a special rootstock that is pest resistant and adapted to the local climate.
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: Place the tree in a sunny location, but with afternoon shade, 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.
The best time to plant a citrus tree is after the danger of frost is past, in late winter or early spring.
Plant the tree so that the root crown is at least one inch above ground level. The top roots must extend out from the trunk, just above, and uncovered by, soil.
Soil: Well drained, can be mixed with aged compost and sand, pH 5.6-8.5 (acidic to alkaline).
Fertilize: Citrus trees are heavy feeders. Apply an organic fertilizer every month from mid-February to early October. Apply a citrus micronutrient solution three times a year in February, May and August. Avoid NPK chemical fertilizers because they increase salt build-up in the soil. Do not fertilize after October to keep the plant from producing new growth that will be harmed by early frost.
Water after becoming established: Basin irrigate or deep water, weekly in summer to monthly in winter, from the trunk to just beyond the canopy. The top of the soil should dry out between waterings. Grapefruit trees require 20% more water than orange trees of the same size. The water should reach 1-2' deep for newly planted trees and 3' deep for trees in the ground 3 years or more. Young trees need watering more often than older trees. A sign of insufficient water is leaves turning dull with inward curling edges.
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.
Prune: Remove sprouts growing on the trunk under the graft as they occur because these are from the wrong plant. Remove dead, damaged, crossing and weak branches in late winter. When shaping into a tree, unshaded trunks and branches should be painted with a tree trunk paint to protect against sunscald.
Keep all grass and vegetation 3' away from the trunk.
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. 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: April, 2020