Citrus Pruning
Julian W. Sauls, Ph. D.
Professor and Extension Horticulturist
Texas AgriLife Extension
January, 2008
Citrus trees normally require little training, since they are headed in the nursery, with three to five scaffold limbs already formed and ready to grow. After planting, trunk sprouts must either be removed by hand, usually several times in the first couple of years, or prevented entirely. Commercial tree wraps installed soon after planting prevent trunk sprouting--as does heavy duty aluminum foil. Too, there are commercial preparations of growth inhibitors which will prevent sprouting when applied to the trunks.
As the orchard matures, occasional root sprouts just seem to appear, even in orchards in which wraps or sprout inhibitors were used. Obviously, the sooner root sprouts are detected and removed, the better, as the 3-inch, hardened spines on older root sprouts can be painful to handle.
Additional minor pruning of broken limbs resulting from equipment misuse is almost a given in Texas citrus orchards, especially during harvesting operations. Few orchards remain undamaged from the careless operation of forklifts and fruit trucks.
Maintenance Pruning
Hedging and topping of citrus orchards are used to control tree size sufficiently to facilitate normal orchard operations, especially pest management, to facilitate harvesting and to maintain optimum productivity. As orchards mature, the tree canopies fill in the space between adjacent trees, grow ever taller and begin to spread into the row middles--and yields continue to increase annually. Ultimately, when the space between adjacent trees is filled and the canopies of adjacent rows are about 7 to 8 feet apart across the middle, the trees have reached the maximum size allowable--and they have also attained optimum production (note that optimum production is not the same as maximum production!). It is at this point when hedging and topping operations should be implemented--waiting even "just one more year" should not even be contemplated.
The failure to control tree size will result in larger trees, and larger trees will produce even larger yields--but only to the point where crowding becomes really severe. Interior limbs and twigs will die, pushing the fruit-bearing growth further and further from the center of the tree. Production will top out at its maximum potential level, after which yields will decrease annually, falling to unacceptably low levels in just a few seasons. Damage to trees--and fruit--and to equipment are unavoidable. Moreover, acceptable pest management in much more difficult to achieve in large, tall trees, as citrus orchard sprayers are not designed for such tree sizes. Harvesting of fruit in the tops of tall trees is unlikely, but that may be a plus, as such fruit rarely has an acceptable packout. Ultimately, severe pruning will be necessary to reduce tree size to normal, which requires the cutting of such large-diameter wood that fruit production will be minimal, if any fruit are produced at all, for at least 2 years afterwards.
Topping should be conducted as soon as hedging is completed, as there is no valid reason to leave the tops unpruned. Some growers prefer to hedge and top the entire orchard at one time, others opt to do alternate middles over 2 years. If hedging cuts will not exceed about 1 foot into the canopy, cutting the entire orchard at one time is viable. However, if pruning has been delayed to the point that deeper cuts into larger wood are necessary, pruning alternate middles would be the better option. Hedging into 1-inch wood will significantly reduce production in the following season, some of which may be offset by increased production in the unpruned middle.
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| Closeup of orchard topped on both sides. | Orchard topped on one side only. |
Equipment
There are basically only two types of mechanical hedging and topping equipment available in Texas citrus--a rotating windmill type which has either three or four arms with a large circular saw blade on each arm and a rigid arm having several overlapping saw blades along its length. Both types do an efficient job, although the windmill type probably does a little better job of brush removal during topping. The angle of either type is readily adjustable for both hedging and topping.
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| Windmill hedger in operation. | Windmill topper in operation. |
Brush Disposal
Rotary shredders do a fair job of chopping up smaller prunings, but do not handle larger-diameter wood so easily. Even then, a single pass with a shredder may not suffice for good brush disposal. Flail shredders or flail choppers are probably more effective and efficient in overall brush removal. In either case, brush disposal is more easily accomplished immediately after pruning while it is still moist and green. Brush that has been allowed to dry out is a little more difficult to destroy.
Season
The best time to hedge and top is during the cooler months, after harvest but prior to bloom. Such timing should be compatible with early, midseason and navel oranges. Valencia oranges usually mature early enough that they can also be pruned in this time frame, but the grower should consult with the packinghouse to assure that Valencia harvest can be completed in time. If Valencia harvest is not completed, then pruning should be delayed until after the spring flush hardens--usually by April.
Grapefruit harvest is rarely completed before spring bloom, so the grower is faced with a serious choice--prune at the preferred time and sacrifice part of the unharvested crop or wait until after the spring flush hardens in April, sacrificing some of next year's crop. It usually makes more economic sense to delay, as the prior season's production expenses are already invested in the mature crop, while little has been spent on the next crop. The relative proportion of the crop that was ring-picked, and the quality and prospects for the remaining fruit can affect the decision. For example, there is no question that the overall packouts of grapefruit drop dramatically after the spring flush--often to levels below breakeven. If returns are expected to be low, e.g., the industry has an abundant crop, and packouts are deemed to be low, hedging may be viable before the completion of harvest.
Pruning Angles
The angle of hedging should be at least 5 degrees, but no more than 25 degrees from vertical--15 degrees is a good compromise between the two extremes. At near-vertical angles, overgrowth of the upper canopy frequently shades out lower limbs, leading to dieback and loss of production in the tree skirts.
The angle of topping should be about the same as used for hedging, but calculated from horizontal. A higher angle will facilitate brush removal from the tops. The height of topping should be about 10 to 12 feet at the shoulder, which will vary with both hedging angle and topping angle. The top center of the tree should be no more than about 13 to 15 feet.
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| Vertically hedged sides. | Sides hedged at 15 degrees. |
Pruning Cycle
In the days of wider tree spacings, hedging and topping practices were usually scheduled on 4-year or 5-year cycles. However, today's orchard spacings and tree densities are such that cycles of 2 or 3 years are necessary. Rio Red grapefruit is rather vigorous, so it will probably require pruning every couple of years. Less vigorous varieties could probably go 3 years between prunings.
Because two main principles of hedging and topping are to limit tree size and to maintain optimal production, which are best achieved by more frequent, light pruning, the best guide to the need to prune again is the rapidity of regrowth of the canopy into the middles. If the mirrors of your Suburban or full-sized pickup routinely bang against fruit or limbs as you drive through the orchard, it is time to prune again.
Pruning and Alternate Bearing
Over the last several seasons, Texas citrus production has been characterized by higher levels during seasons which bloomed in even-numbered years (e.g., the 2000-01 season), followed by lower production in odd-numbered seasons (e.g., the 2001-02 season). This alternating tendency exists across all varieties. Some orchards do not exhibit alternation, while others which do are out of phase with the industry, being up when the industry is down and down when the industry is up.
Alternate bearing persists because the tree uses most of its reserves and available nutrients to mature a larger-than-normal crop, with little energy being left to provide sufficient growth for the next crop. Consequently, the following crop is lighter, so the tree produces more growth than normal, setting up yet another year of higher production. If not attenuated, the highs and lows become further and further apart.
To attenuate alternate bearing, pruning and fertilization are about the only options which growers can alter, the latter of which is discussed in another publication. For pruning to be effective, it must be done after the end of an "off" or light-crop year, i.e., prior to the season of anticipated high production. It should not matter whether the pruning is conducted before or after the bloom, as the results should be about the same--reduction in production during the season following pruning. If alternate bearing is very strong, the entire orchard should be hedged and topped at the same time. By lowering production in a heavy crop year by pruning, with the appropriate alterations in the fertilizer program, the alternate bearing cycle can be attenuated. However, alternate bearing developed over several seasons, so it may require several seasons to eliminate.
Fertilization
Routine hedging and topping practices carried out in a timely fashion should not require any changes in the orchard fertilization program. If, however, hedging and topping cuts are severe, i.e., cuts of 1-inch or larger wood, the fertilizer program should be adjusted accordingly. Basically, severe pruning results in vigorous regrowth and reduced fruit set--to avoid large, coarse-skinned, mal-formed fruit, the fertilizer program must be reduced.
Rehabilitative Pruning
Rehabilitative pruning is used to remove the dead wood resulting from freeze damage and to develop a totally new canopy. Hedging and topping equipment can be used to remove the outer canopy killed by a moderate freeze, but hand-operated equipment is necessary to buckhorn trees damaged by a severe freeze. In the latter situation, hedging equipment can be employed to remove a significant portion of the canopy to facilitate the final buckhorning operation.
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| Rehabilitative pruning after severe freeze. | Pruned too early, then bulldozed. |
The prevailing tendency following a freeze is to begin rehabilitation pruning immediately. However, any freeze severe enough to result in defoliation cannot be immediately evaluated as to the severity of wood damage. Guessing at the extent of damage can be costly, as some growers learned after the 1983 freeze. In that freeze, some orchards which were pruned before and during the spring flush were almost completely dead by the end of summer, at which time they were bulldozed.
Experience from previous severe freezes has clearly proven the advantages of delaying pruning decisions until a complete assessment of the extent of damage can be conducted. Early summer is about as early as damage evaluations can be accurately made because much of the spring regrowth will die before summer due to underlying wood or bark damage. Dieback can and does occur for 2 years or more following a major freeze. Consequently, rehabilitative pruning should be delayed until after the spring growth flush matures in early summer.
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This page updated January 7, 2008.