Grapefruit

Grapefruit, Citrus × paradisi, is a large evergreen tree in the family Rutaceae grown for its edible fruit. The tree has a spreading canopy with a rounded top and densely packed dark green, long and thin leaves with winged petioles. The tree produces white flowers singly or in clusters and large spherical fruits, usually in clusters. The fruits are 8–12 cm (3–5 in) in diameter with yellow-orange skin and segmented white, red or pink flesh. Grapefruit trees can reach heights between 10 and 15 m (33–50 ft) and live for many years if well maintained. Grapefruit likely originated in the West Indies as a hybrid of pomelo and sweet orange or mandarin.


Grapefruit can be eaten fresh and is commonly eaten as a breakfast fruit. It can also be used to make juice or processed for canning of segments or pulp. Grapefruit essential oils are used in perfumery.


Requirements Grapefruit is a tropical to subtropical plant and the trees grow best in areas with hot daytime temperatures and warm to hot night time temperatures. Grapefruit is less hardy than orange but continual exposure to cooler temperatures will induce a certain degree of cold tolerance. Mature trees can tolerate short exposures to temperatures below freezing but ice will begin to form in fruit after 2-3 hours at -3°C (27°F). Young trees may be killed by these temperatures. young trees will be killed. Fruit will also be damaged by freezing conditions. The trees will tolerate drought conditions but perform poorly in water-logged soil. Trees will grow best when planted in a well-draining sandy loam with a pH between 6.0 and 7.5. Soil must be deep enough to permit adequate root development. Grapefruit trees will grow best when planted in full sun. Grapefruit propagation Grapefruit seedlings are usually produced by grafting or budding to an appropriate rootstock as seeds will not produce fruit true to type. Grafting is the process by which a scion from plant is joined to the rootstock of another to produce a new tree. Budding is a special type of grafting where the scion that is joined to the rootstock consists of a single bud. Budding is commonly used in citrus propagation as it is the easier of the two processes and works very well. Common rootstocks for grafting and budding of citrus trees include sour orange and rough lemon. Budding Budding should be carried out when seedling stems have reached roughly the diameter of a pencil (6–9 mm/0.25–0.36 in) and at a time when the bark of the rootstock tree is slipping (this is the term used to describe a period of active growth when the bark can be easily peeled from the plant). Twigs (budwood) should be collected from the previous growth flush or the current flush so long as the twig has begun to harden. The twigs should have well developed buds and should be as close as possible to the diameter of the rootstock onto which it will be joined. It is extremely important to only collect budwood from disease-free trees. The use of diseased budwood can cause the spread of many serious citrus diseases which can kill trees. The budwood to be used for propagation should be trimmed to create budsticks which are 20–25 cm (8–10 in) by removing any unwanted wood and leaves. These budsticks can be stored for 2–3 months under the correct conditions but it is best to use them as soon as possible after cutting. The simplest way to join the budwood the the rootstock is by T-budding. The area to be joined should be pruned to remove any thorns or twigs and the cut made approximately 15 cm (6 in) from the ground. Using a sharp knife, a 2.5–3.8 cm (1–1.5 in) vertical cut should be made in the stem of the rootstock, through the bark. A horizontal cut should be made at either the top or the bottom of the vertical cut to produce a “T-shape” The horizontal cut should be made a slightly upward-pointing angle and should reach through the bark. Remove a bud from a budstick by slicing a thin, shield-shaped piece of bark and wood from the stem, beginning about 1.25 cm (0.5 in) above the bud. This piece should measure 1.9–2.5 cm(0.75–1.0 in) in length. Immedietely insert the piece of bud into the cut on the rootstock by sliding it under the opened bark so that the cut surface lies flat against the wood of the rootstock plant. Finish the join by wrapping the bud with budding tape. After the union has formed and the tape is removed, the bud is forced to grow by cutting the rootstock stem 2.5–3.9 cm (1.0–1.5 in) above the join about 2/3 of the way through the stem on the same side as the join. The top of the seedling should then be pushed over towards the ground. This process, known as “lopping” allows all of the nutrients to be diverted to the bud Once the bud begins to grow and reaches several inches in lengthe, the lop can be removed completely from the seedling. Planting seedlings Grapefruit trees can be purchased as seedlings which have already been grafted and only require planting in the garden or orchard. The best time to plant citrus trees is in Spring after all danger of frost has passed in your area. Trees should be planted at or higher than the level of the nursery pot. Once the tree is positioned in the planting hole, backfill the soil by about half and water to allow the soil to settle around the lower roots before filling in the hole. The newly planted tree should be watered every few days. General care Newly planted trees require proper irrigation to ensure they become established. During the first year, water should be applied at the base of the trunk so that the root ball is kept moist to allow the roots to establish in the soil. Newly planted trees should be provided with water every 3–7 days. The soil should be moist, but not wet. Trees planted in sandy soils will require water more frequently. Young trees will also require a light application of fertilizer every month in the first year. Grapefruit trees will need protected from cold temperatures to prevent damage. Soil can be mounded up around the trunk during the winter and removed in the Spring. Young trees can also be protected from frosts by covering them with tarps or blankets as required.


CABI Crop Protection Compendium. (2008). Citrus x paradisi datasheet. Available at: http://www.cabi.org/cpc/datasheet/13461. [Accessed 12 December 14]. Paid subscription required. Timmer, L. W., Garnsey, S. M. & Graham, J. H. (2000). Compendium of Citrus Diseases. American Phytopathological Society Press. Available at: http://www.apsnet.org/apsstore/shopapspress/Pages/42481.aspx. Available for purchase from APS Press. Williamson, J. G. (1997). The Grapefruit. University of Florida Cooperative Extension Service. Available at: http://university.uog.edu/cals/people/PUBS/Grapefrt/CH06300.pdf. [Accessed 15 December 14]. Free to access.