Orange

Orange, Citrus sinensis, is an evergreen tree in the family Rutaceae grown for its edible fruit. The orange tree is branched with a rounded crown and possesses elliptical or oval leaves which are alternately arranged on the branches. The leaves have narrowly winged petioles, a feature that distinguishes it from bitter orange, which has broadly winged petioles. The tree produces white flowers singly or clustered on a raceme. The fruit is a spherical berry with a green-yellow to orange skin covered in indented glands and a segmented pulpy flesh and several seeds. Orange trees can grow to a height of 6–15 m (16–49 ft) and can live for periods in excess of 100 years. Most plantations have an economic lifespan of around 30 years. Orange may also be referred to as sweet orange or navel orange and is believed to have originated from a wild ancestor in the border between Vietnam and China.


Oranges can be consumed as a fresh fruit and are commonly pressed or squeezed to produce orange juice.


Requirements Orange is a subtropical plant and the trees grow best in regions with a pronounced change in season. They will grow best at temperatures between 12.8 and 37.8°C (55–100°F) during the growing season and 1.7 to 10°C (35–50°F) during dormancy. Mature orange trees can survive short periods of freezing, whereas young trees will be killed. Trees should be protected from frosts and freezing conditions to prevent damage. The trees will also 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. Orange trees require full sun and should be protected from wind which can cause damage to the trees. Orange propagation Orange 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 one 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. 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. When the union is made and the tape is removed, the bud is forced to grow by cutting the rootstock stem above the join about 2/3 of the way through the stem. This cut should be made 2.5–3.9 cm (1.0–1.5 in) 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 Orange 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. Standard sized trees should be spaced 3.7–7.6 m (12–25 ft) apart in an area that receives full sunlight, but is protected from strong winds which can damage the trees. Planting against a south facing wall will help protect the tree in cooler climates. 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.


CABI Crop Protection Compendium. (2010). Citrus sinensis (navel orange) datasheet. Available at: http://www.cabi.org/cpc/datasheet/13466. [Accessed 02 March 15]. Paid subscription required. Lacey, K., Ramsey, H. & Hoffman, H. (2009). Growing healthy citrus. Government of Western Australia Department of Agriculture and Food. Available at: http://archive.agric.wa.gov.au/objtwr/imported_assets/content/hort/fn/cp/citrus_propagation.pdf. [Accessed 02 March 15]. Free to access. Lazaneo, V. (2008). Citrus for the home garden. University of California Cooperative Extension. Available at: http://www.mastergardenerssandiego.org/downloads/citrus%20for%20home%20garden.pdf. [Accessed 02 March 15]. Free to access. 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. & Jackson, L. K. (1994). Citrus propagation. University of Florida Cooperative Extension Service. Available at: http://www.ultimatecitrus.com/pdf/propagation.pdf. [Accessed 02 March 15]. Free to access.