Fact Sheet HS-144 June 1994 Citrus Tree Pruning Principles and Practices1 D.P.H. Tucker, T.A. Wheaton and R.P. Muraro2 Figure 1. Pruning for Canopy Bearing Surface of Citrus Trees. Pruning healthy, mature citrus trees usually required for future canopy bearing surface reduces yield in proportion to the amount of foliage development and for the conduct of efficient cultural removed and can delay fruiting of young, nonbearing and harvesting operations (Figure 1). The pruning trees. Pruning should therefore be limited to that process 1) adjusts tree shape and the ratio of 1. This document is Fact Sheet HS-144, a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date: June 1992. Reviewed: June 1994. 2. D. P. H. Tucker, professor, extension horticulturist, Department of Horticultural Sciences; T. A. Wheaton, professor, horticulturist, Department of Horticultural Sciences; R. P. Muraro, associate professor, extension economist, Department of Food and Resource Economics, Citrus Research and Education Center, Lake Alfred, Florida, a branch of the University of Florida, Gainesville, Florida. The use of trade names in this publication is solely for the purpose of providing specific information. It is not a guarantee or warranty of the products named, and does not signify that they are approved to the exclusion of others of suitable composition. The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / Christine Taylor Stephens, Dean Citrus Tree Pruning Principles and Practices Page 2 framework to fruit bearing shell of the canopy, 2) HORMONAL RELATIONSHIPS AND APICAL alters the top/root ratio, and 3) changes the DOMINANCE carbohydrate (food storage) status of the tree. Proper control of vegetative growth is essential for the While hormones occurring in the citrus tree affect maintenance of healthy, productive citrus groves. fruit set, the effects of pruning on their action is not Most groves in Florida must be pruned at some time well understood. Suppression of lateral bud growth during their development to avoid problems by the terminal bud is known as apical dominance. associated with overcrowded, excessively tall trees. Apical dominance explains many of the growth When pruning should begin will depend to a large characteristics of trees and their responses to pruning. degree on the initial tree planting density. Crowded Branching is influenced by an auxin produced in the conditions result in poor light accessibility, loss of terminal bud which moves down the system to inhibit lower foliage and bearing wood, relocation of fruiting lateral bud break. Removal of the terminal bud to the upper tree canopy areas and reduction in fruit destroys apical dominance so that one or several yield, size, and external quality. Good management lateral buds will commence to grow and branching therefore dictates the need to prune before the results. Vigorous shoots called water sprouts or occurrence of these undesirable effects. suckers show extreme apical dominance with no side-branch development. Apical dominance varies The response to pruning depends on several somewhat with vigor and variety. factors including variety, tree age and vigor, fruiting habits, growing conditions, and production practices. BEARING HABITS As no one system or set of rules is adequate for the numerous situations encountered in the field, growers The balance between tree growth and fruitfulness are encouraged to gain a clear understanding of the appears to depend, to some extent, upon a principles involved in pruning and to take advantage relationship between carbohydrates and nitrogenous of research results and knowledgeable colleague and compounds within the tree. When both are adequate, custom operators’ observations. moderate growth and high yields occur. When both are low, citrus trees grow and fruit poorly. A tree low SUNLIGHT, PHOTOSYNTHESIS, AND FOOD in carbohydrates and high in nitrogen tends to STORAGE produce vigorous vegetative growth at the expense of fruit production. Since carbohydrates are The importance of sunlight intercepted by the manufactured and stored in the leaves, heavy pruning tree canopy on the production of high yields of good which removes a large portion of the leaf area can quality fruit cannot be overemphasized. Light result in this condition. Too much nitrogen after provides the energy for photosynthesis in which severe pruning can aggravate the problem, causing carbon dioxide from the air and water from the soil thick and puffy fruit peel. Nitrogen applications are combined in the leaves to form the basic foods should therefore be adjusted to the severity of upon which trees live, grow, and bear fruit. Light pruning. Reducing nitrogen applications avoids an becomes a limiting factor in crowded groves and imbalance when heavy pruning is done. Omitting a pruning improves light access. Adjustments must be nitrogen application before heavy pruning and made in tree height, row middle width, and hedging possibly after will reduce both costs and excessive angle to maximize sunlight impingement on the tree vegetative growth. The length of time this limitation canopy. Sunlight not only influences flowering and should continue will depend upon the severity of fruit set but also enhances fruit quality and color pruning and the rate of top recovery. Light development. maintenance pruning should not affect fertilizer requirements. In citrus, carbohydrates are stored in leaves, twigs, and branches with only a minor amount going to the Some citrus groves tend to have a bearing habit root system. The maximum amount of stored food is with alternating high and low yields. A heavy crop of reached in spring just before the onset of growth flush fruit tends to deplete carbohydrates and results in a activity. The foliage of citrus trees therefore acts as small crop and increased vegetative growth the an important food storage area, and heavy pruning following year. Pruning after a heavy crop causes the tree to produce vegetative growth at the additionally stimulates vegetative growth the following expense of fruit production. year because the carbohydrate supply has been somewhat depleted and the capacity to resupply has Citrus Tree Pruning Principles and Practices Page 3 been reduced. Poor fruit quality may also result from although this can vary with tree vigor, grove this practice. Pruning after a light crop and before an conditions, and the size of the previous crop. expected heavy crop should help reduce alternate bearing. SUGGESTED PRUNING PRACTICES The orientation of branches in space has a Young Trees marked effect on growth and fruiting. A decrease in growth rate and an increase in flowering occurs when Severe pruning and training of young, nonbearing branches bend to a horizontal position. A possible trees tends to delay fruit production and should be explanation for this phenomenon is a change in the avoided. Most trees usually need no pruning for the distribution of growth substances and carbohydrates. first few years in the grove except for removal of Favoring horizontal branches over upright ones sprouts on the trunk. These can be easily brushed off should result in better growth control and more fruit when young and tender and the wounds will be small. production. Larger sprouts should be cut off flush with the trunk. Sprouting on the trunks of young, nonbearing trees BASIC PRUNING CUTS can be greatly reduced by using a commercial sprout inhibitor containing naphthaleneacetic acid. While Heading back and thinning out are the main types protective wraps around the trunk will reduce of pruning cuts and are used for somewhat opposing sprouting, careful observation is required to avoid objectives. Heading back removes the terminal insect and disease problems under the wraps. portion of a shoot or branch, destroying apical Occasionally, a vigorous sucker will dominate a weak dominance and stimulating lateral bud breaks. This tree or a sucker may arise from the rootstock. These tends to produce a more bushy, compact tree. should be removed early before they compete with Mechanical hedging and topping are forms of mass more desirable growth. Selection of permanent heading back. As the individual tree or hedge row scaffold branches during the first few years is rarely increases in size, internal wood may become less successful since the natural growth habit of these productive and eventually die. Thinning out involves trees is so unpredictable. New growth may occur at the removal of complete branches to laterals or to the unexpected places and become dominant over main trunk and is done by selective pruning with selected branches. When the tree is 3 or 4 years old, hand-held equipment. It encourages longer growth of depending on its growth, branches that are too closely the remaining terminals and can result in a larger, spaced or are crossed and entangled may be removed. more open tree. This type of pruning may be done This pruning should be light, just sufficient to for better