Citrus Orchard Establishment

Julian W. Sauls, Ph. D.
Professor and Extension Horticulturist
Texas AgriLife Extension


Site Selection



Major factors which determine the suitability of a particular site for citrus orchard establishment are soil, water, topography and the closely related factors of salinity and drainage.

Soils

The Brennan, Delfina, Hidalgo and Willacy soil series comprise the major acreages of soils which are well-suited to citrus production, although smaller acreages in other soil series also are well-suited for citrus. An examination of local soil survey maps can provide useful information about a potential orchard site.

The best citrus soils are coarse sandy loams to fine sandy clay loams, deep and well-drained, with a ground water table at or below the 5 -foot depth. Salinity should be less than 2 millimhos per centimeter. Soil pH normally will be in the range of 7.0 to 8.2. Soils containing more than 30 percent clay in the upper 2 feet generally restrict root development, tree size and orchard productivity.

Occasional relatively impermeable clay lenses may occur in otherwise suitable soils. In such cases, drainage installation is necessary to prevent salinity accumulation and high water table, either of which could severely restrict root growth and, thus, affect overall tree vigor and productivity.

Topography

The principal citrus-producing counties of Cameron, Hidalgo and Willacy are situated in a flat and featureless plane with poor natural drainage. Elevation increases from sea level at the coast to 37 feet at Harlingen, 75 feet at Weslaco, 96 feet at Edinburg and 225 feet at McCook.

Although terrain features are poorly defined, they should be used where possible. Existing slight differences in slope and elevation determine the rate of cold air movement into or away from a site on calm, clear nights. During radiational freezes with wind speeds under 4 mph, cold air will settle in the lowest area, resulting in temperatures a few degrees lower than in slightly higher surrounding areas. During advective freezes with strong northerly winds, orchards on exposed northern slopes and atop small ridges may be subjected to colder temperatures than those occurring on southern slopes.

Water

Citrus requires about 45 to50 inches of water annually. Average rainfall across the Valley normally provides less than half of the annual water requirement. Consequently, irrigation must provide 25 to 30 inches of water annually to supplement existing rainfall.

The major water source for the Valley is the Rio Grande River and its storage reservoirs at Falcon Lake and Lake Amistad. This water is allocated to both Texas and Mexico for municipal, industrial and agricultural use. Depending upon annual rainfall in the Rio Grande watersheds, water shortages occur and may become quite severe. All water from the river is apportioned by allotment to the respective irrigation districts and other water rights holders.

Rio Grande water is considered moderately saline, usually containing 500 to 1,000 ppm total salts. During some seasons, higher salinity levels in the irrigation water can occur, especially at points farther from the river.

Very little ground water is used for citrus irrigation in the Valley, although suitable well water does exist in some areas.. Generally, wells containing 300 to 1,200 ppm total salts, less than 1.0 ppm boron and a sodium adsorption ratio (SAR) less than 8 will not limit citrus production on well-drained soils, particularly with sour orange rootstock. Well water having an SAR of 8 to 15 is considered marginal.

Potential orchard sites should be checked for salinity. Those with salinity below 1,280 ppm in the soil saturation extract should pose no problems for citrus. Those with a salinity level up to 2,560 ppm can be productive with intermittent leaching and more frequent irrigation.

Because salinity can increase in soils under Valley conditions, careful management of irrigation and drainage is essential to good citrus productivity. Each irrigation should provide adequate water to replenish the soil reservoir, with an occasional excess irrigation to provide leaching of accumulated salts from the root zone. Moreover, the normally heavy rains in May and September provide thorough leaching.

Internal drainage and depth of the water table should be checked before planting. Excessive free water in the soil profile because of poor drainage results in poor aeration, poor soil structure and excessive soluble salts. Such problems in existing orchards may not be recognized until trees begin to defoliate, become less productive or show dieback and poor growth.

Surface drainage is provided during land preparation and installation of an irrigation system. Subsurface drainage, if needed, must be designed and installed to remove excess water to drainage outlets or to collection points where it can be discharged into drainage ditches.

Land Preparation


Orchard sites should be leveled to the appropriate grade to facilitate uniform water distribution and surface drainage. Assistance in planning land leveling can be obtained from the Farm Service Agency of the USDA, which has local offices in each county. After leveling, the soil should be deep-chiseled to break up compacted areas and surface hardpans, then disked thoroughly in preparation for planting.

Orchard Design and Spacing


It is generally accepted that a north-south row orientation provides better production and fruit quality than an east-west orientation. Moreover, single rows of trees have proven more feasible to manage than various configurations of double-row plantings.

The long-term trend toward closer tree spacings in Texas citrus orchards continues. Obviously, more trees provide more fruit per acre during the years until the trees fill the available space between trees. In addition, higher densities are considered to have better cold protection and may reduce windscarring of fruit. However, closer spacings are more expensive to install and require more intensive management at maturity to control tree size and maintain optimum productivity.

Most grapefruit orchards are planted at 24 or 25 feet between rows, while 24 feet is common for most oranges. Marrs oranges can be planted as closely as 22 feet, as Marrs trees do not spread so much as other oranges. The minimum row width is dictated by final tree size to be maintained and the space required for orchard care equipment and harvest operations.

In-row spacings of 12.5 and 15 feet are most common, but some closer spacings exist. Minimum in-row spacing is determined by the economics of nursery tree and planting costs, young tree cold protection costs and subsequent pruning and/or tree removal costs, if the latter is planned as a thinning operation.

Limited testing of very high density plantings, using microbudded trees, has shown very high yields during the first years of production. However, these trials have not been in place sufficiently long to assess production and management practices in later years.

Table 1. Trees per acre at various spacings (in feet).
8
Row
width
In-row spacing
8 9 10 11 12 13 14 15
20 272 242 218 198 181 168 156 145
21 259 230 207 189 173 160 148 138
22 247 220 198 180 165 152 141 132
23 237 210 189 172 158 146 135 126
24 227 202 181 165 151 140 130 121
25 218 194 174 158 145 134 124 116


Planting


Most citrus trees are planted from October through April, although planting at any time can be successful if the trees are given the proper care for the season. Fall planting allows reestablishment of the root system prior to spring growth, although very early planting could result in succulent growth that is easily damaged by later cold weather. Late December and January planting is excellent because the trees should be completely dormant, and the weather is usually cool enough that top growth is not initiated until the period of greatest freeze danger is over. Planting from February through May does not allow adequate time for root establishment before top growth begins, so more frequent irrigations must be applied to carry the trees through the heat of late spring and summer.

The orchard site should be laid out and planting holes dug prior to receiving the trees. While a surveyor's transit can be used to lay out the orchard, such precision is rarely justified. Most growers simply square up the corners of the site to lay out the end trees of each row. The first row of trees is laid out using stout nylon cord very tightly stretched between the two end-tree sites of the row, with a fixed loop over metal stakes driven into the ground at each end tree. In-row tree spacings are measured along the string, with some means to mark the spot of each tree. Small plastic stakes are used, as are pieces of tissue paper held in place with a clod of soil.

A novel method that works best if the soil of the orchard site is crusted over from a recent rain shower is to use a suitable fluorescent aerosol spray paint to mark a quarter-sized spot on the soil and on the string. After measuring and marking the first row, subsequent rows are marked simply by moving the string and spraying the soil surface at each already-painted spot on the string.

Probably the most common method of digging the holes is by use of a tractor-mounted, 9-inch auger (post-hole digger). The tree planting sites should be easily visible from the tractor seat, whether marked with stakes, paper or paint, so that the operator can easily position the auger at each site. To assist the operator to gauge the depth of drilling, spray paint the desired depth on the shaft of the auger with fluorescent paint.

Field-grown Trees

The tops of field-grown trees are pruned substantially at digging to bring them into closer balance with the reduced root systems. Trees should be planted as soon as possible after digging. Root balls should be watered daily if the trees must be held between digging and planting.

At planting, the top of the ball should be set level with or slightly above soil level. Because most nurseries use nylon twine to secure the burlap around the root ball, the twine should be cut where it encircles the trunk of the tree--failure to do so could result in girdling of the young tree, since nylon may take years to decompose. Some growers cut the twine sufficiently to allow the burlap to be folded down into the planting hole for quicker deterioration, though such practice is not really necessary. The planting hole is then completely filled and tamped to eliminate air pockets. Newly-planted trees should be watered as soon as possible to settle the tree and soil and to provide the initial moisture needed for establishment.

Container-grown Trees

It may be preferable to delay planting of container-grown trees until January or February. Earlier plantings are quite successful, but the trees often resume growth in the field, which would be subject to cold damage in the winter.

The major concern in planting container-grown trees seems to be the slowness of the root system to move out of the original, soilless medium and into the surrounding soil, thus requiring more intensive irrigation until the trees become established. This situation can be greatly alleviated by the removal of the outer 1 -inch layer of medium at planting. This allows the outer parts of the root system to be in direct contact with surrounding soil, so the trees become established more quickly. Even so, intensive irrigation management is essential.

The top of the root system should be set at or slightly above soil level. Either the top inch or so of medium should be removed and replaced with soil at planting or a 1-inch layer of soil should be placed over the medium as the final step in planting. The soilless medium has very good drainage; i.e., it contains considerable air space. Without sealing off unrestricted air movement into and out of the root ball, the medium will quickly dry out, causing moisture stress of the tree even though surrounding soil may be quite moist. Trees should be watered as soon as possible following planting to settle the tree and soil and to provide the initial moisture needed for establishment.

Tree Wraps


Most Texas citrus growers routinely install tree wraps at planting. A major reason growers use wraps is to eliminate sprouting along the trunk. Without wraps, the trunks would have to be treated with a sprout-inhibiting growth regulator soon after planting, or the sprouts would have to be removed by hand several times during the first couple of seasons. Wraps also protect the trunks from damage caused by wind-blown sand, from gnawing by rodents (primarily rabbits and jackrabbits) and from direct contact with herbicides during applications for weed control.

Any number of available wraps will meet these criteria, including heavyweight aluminum foil, without also raising the temperature underneath the wrap to potentially damaging levels. One downside to wraps is the potential for ants to tunnel or nest underneath the wrap, leading to Phytophthora infections that may extend into the scaffolding of the developing tree. That possibility causes most growers to apply a suitable combination of insecticide and fungicide to the trunks prior to installing the wraps.

Tree wraps are also widely perceived to provide significant cold protection to the young trunk, but protection is not so great as most growers believe. Generally, most wraps can provide only a few degrees of cold protection--and that for only a few hours. During an extended freeze over several days, only the Reese Insulator® continues to protect the trunks from freezing. While this wrap also includes an insecticide to combat insect infestations under the wrap, its cost is several times that of most other wraps.

Irrigation


Young citrus trees require intensive irrigation management to prevent moisture stress. Obviously, irrigation frequency depends upon soil type, prevailing weather and type of irrigation system. Growers are expected to modify irrigation frequency based upon these factors and their own experience.

For flood irrigation, strip borders should be used during at least the first year to conserve water, although strip borders require more work to install and maintain, particularly with respect to weed control on the borders. Single drip irrigation lines are very effective for orchard establishment and for water conservation, but double lines on each row would be better for orchard performance 3 or 4 years after planting. Microsprayer irrigation systems are highly recommended for both orchard establishment and mature orchard water management, and have the added advantage of providing some measure of cold protection in the orchard.

Nutrition


Nitrogen is the only major nutritional element that must be applied to Valley citrus, although micro-element deficiencies may occasionally require correction. Fertilizer should be first applied when growth resumes following planting and periodically thereafter. The fertilizer should be evenly distributed atop the soil over the expanding root zone. Both drip and microsprayer irrigation systems can be used very effectively and efficiently to apply liquid fertilizer periodically during irrigations.

General recommendations are 1/8, 1/4 and 1/2 pound of actual nitrogen per tree annually for the first, second and third years, respectively. However, some growers routinely apply higher amounts with good success during establishment.

Weed Control


Complete weed control around young citrus trees is essential because weeds compete for available moisture, nutrients and sunlight. Indeed, tree growth and development are severely restricted by weed competition.

Although mechanical means of weed control are still used, the majority of young orchards are established under chemical weed control, particularly in strips along the tree row. A number of proven herbicides, both pre-emergent and post-emergent, are available for use in young citrus.

Pre-emergent herbicides normally are applied during early spring and late summer, whereas post-emergent materials are applied as needed to control those weeds which escape the pre-emerge program. Good herbicidal weed control may be difficult to attain in the first season.

Pruning and Training


Young citrus trees normally are pruned and trained in the nursery. Consequently, little pruning is required during establishment. Most pruning is limited to the removal of rootstock sprouts, trunk sprouts, occasional twig dieback and water sprouts that outgrow the rest of the tree.

Orchard Productivity


Orchard productivity can vary considerably because of natural causes, rootstock-scion combinations and level of management. However, general production estimates are essential for management decisions. Estimates based on historical production data in Texas orchards can be used by growers to project production trends.

The data in Table 2 are based on a standard orchard density of 115 to 120 trees per acre, under three levels of management. Orchards of higher density should produce somewhat higher yields, within limits, in the first 3 to 7 years. Obviously, yields may vary in any given year because of weather and general orchard management and because of the occurrence of alternate bearing.

Table 2. Tons of citrus produced per acre under three levels of management.
Grapefruit Early Oranges Valencia
Age Fair Avg. Very
good
Fair Avg. Very
good
Fair Avg. Very
good
3 1 3 6 1 2 4 1 2 3
4 3 6 10 2 5 7 2 3 4
5 5 9 14 4 7 11 3 4 7
6 7 14 19 5 10 13 4 7 10
7 8 18 23 7 13 16 5 9 13
8 10 20 26 8 15 19 6 11 15
9 11 22 27 9 17 22 7 13 17
10+ 12 23 28 10 18 24 8 14 18


Navel oranges are notoriously low-yielding, although the local N33E selection is more productive than most navel orange varieties. In general, navel production will be in the range of about half that of early oranges shown in Table 2 above.


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This page revised January 7, 2008, by Julian W. Sauls, Ph. D.

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