San Antonio Express News
Sunday, January 23, 2005
Last week we discussed the care of established citrus trees and focused on timely freeze protection and rehabilitation. Today Extension will discuss soil requirements, site selection, varieties, planting and care. Even though it may be chilly and gray outside, this is the perfect time of year to be selecting your citrus and nurseries should be receiving fresh stock anytime.
All citrus trees require deep soil having both good surface and internal drainage. Surface drainage refers to runoff to prevent water standing around the tree. Internal drainage is the ability for water to percolate downward through the soil to preclude saturation of the root zone.
The presence of vigorous, healthy landscape trees is a good indication that the soil is sufficiently deep and well-drained for citrus trees. To test the drainage in your landscape, dig a posthole 3 to 4 feet deep and fill it with water. All water should drain from the hole within 24 to 36 hours. Soils requiring more than 48 hours to drain completely should be avoided unless raised planting beds are used.
Most citrus grows well in a soil pH range from 6 to 8. Avoid soils that have a high caliche content or are excessively salty, as citrus trees will not grow well in such soils.
Citrus requires full sunlight for optimum growth and production. In cold-sensitive areas, plant citrus trees on the south and southeast side of the house to provide some protection from northwesterly cold fronts. Plant 6 to 8 feet from buildings, driveways, walkways and fences, and twice that far from each other. The natural form of citrus is for the ends of the lower branches to almost touch the ground when fruit is present, so allow for this natural growth at planting. Avoid planting near septic tank lines, underground cables or too close to other large trees, so as to prevent roots problems at a later date.
Varieties, Selection and Planting
“Seedling” citrus trees are those grown from seed. Some productive seedlings do exist in Texas, but very few have the quality of named varieties. Although the seed of some types of citrus come true-to-type, seedlings which do not are usually thorny, slow to come into production and frequently produce seedy fruit. Seedling trees are more cold-hardy than budded trees, an advantage they lose upon being budded, but most seedlings are more susceptible to foot rot. Most citrus are budded onto “rootstocks” which are better adapted to certain soil conditions. Most citrus trees are of a desirable scion variety T-budded onto a seedling rootstock several inches above the soil line. The rootstock of a budded tree includes all roots and the lower few inches of the trunk, whereas the scion is the trunk and all branches, leaves and fruit.
Sour orange, the most common rootstock in Texas, is well-adapted to most soil conditions. Trifoliate orange is more cold-hardy than sour orange and produces a smaller tree, but it is not well adapted to saline or highly alkaline soils. Consequently, trifoliate orange is preferred for the upper Gulf Coast and colder areas where soil conditions are suitable, but sour orange is recommended for the lower coast and most of southern Texas.
When given the proper growing conditions and care, the following varieties have done well in Bexar County: Oranges-Satsuma-mandarin (technically, a tangerine and the highest quality citrus with most cold resistance), Pineapple, Valencia, Hamlin; Lemons-Improved Meyer; Limes-Mexican (or Key); Grapefruit-Rio Red, Ruby Red; Tangerines-Clementine (Algerian), Dancy; Tangelos-Orlando, Minnelos.
Most citrus nursery stock is containerized, either having been grown entirely in containers or field-grown and transplanted to containers prior to sale. Normally, the bud union will be readily discernible as a cut area at a dogleg bend in the trunk. The cut area is where the top of the rootstock was cut off to allow the budded top to grow erect. This area should be healing over with bark at the time of purchase. The crook in the trunk will disappear within a couple of years, but the bud union will remain discernible for years as a distinct line of contrast between bark textures of the stock and scion. Planting during fall to late winter allows the tree to become better established before the onset of hot, dry weather of late spring and summer.
Most container citrus trees are grown in a soil-free medium that usually contains a fair proportion of peat moss. The roots of such trees tend to remain within the growing medium long after planting; thereby, resulting in poor establishment and growth. To avoid this problem, wash off an inch or more of the growing medium all around the root ball, including the top, immediately before setting the tree in the ground.
Planting depth is critical to survival. The rootstock is somewhat resistant to foot rot disease, but the top is quite susceptible. If the bud union is too low with respect to surrounding ground, the tree could contract foot rot and die. The practice of scooping out grass and soil to form a large depression (below ground level) for ease of watering almost guarantees the death of a citrus tree. Remove lawn grass in a circle 3 to 5 feet in diameter, centered on the planting hole. Dig the planting hole twice as wide as the root ball. In a bare ground situation, dig the hole exactly the same depth as the root ball, but in lawn grass, dig it 1 inch less than the root ball depth. The best way to determine proper depth is to lay a shovel handle or similar object across the hole, with both ends laying on undisturbed ground or the lawn grass.
Mixing topsoil, compost, peat or other materials with the backfill soil is unnecessary in good citrus soils. Set the tree in the hole, backfill about halfway, then water sufficiently to wet the backfill and settle it around the roots. Finish filling the hole and tamp the soil lightly into place. Cover the root ball with 1/2 to 1 inch of soil to seal the growing medium from direct contact with the air and prevent rapid drying of the root ball.
Build a watering ring atop the ground around the tree, about 5 to 6 inches high and 6 to 8 inches thick. The ring should be slightly wider than the planting hole. Fill the water basin with water. When the water soaks in, it may be necessary to add a little soil to the holes made as the soil settled around the root system.
Water and Nutrition
Newly-planted citrus trees require thorough watering 1-3 times the first week and 1-2 times per week for the next few weeks, depending upon soil type, rainfall and time of year. Then, apply water when the soil begins to get dry an inch or so down. Simply fill the water ring each time. The watering ring should erode away over time (4 to 6 months), at which time the tree can be considered established. Water as needed by soaker hose or sprinkler system.
Do not apply fertilizer until the tree begins new growth after planting. Fertilize monthly through October. Scatter fertilizer on the ground at least a foot from the tree trunk and promptly water it in thoroughly. Nitrogen is usually the only fertilizer element required in most Texas soils, but additional elements should not do any harm. Consult your local county Extension agent.
Good weed control is essential for rapid establishment and vigorous growth of young citrus trees. Eliminate all existing lawn grass and weeds for several feet around the tree. As the spread of the tree increases, widen the grass-free area beyond the tree canopy or drip-line.
Citrus trees are sold already properly shaped and pruned to develop naturally, so pruning and training of a citrus tree is not necessary. The only exception is that shoots from below the head (scaffold limbs), whether on the rootstock or the scion, should be removed as soon as they are noted.
If space is a problem in your landscape, consider “patio” or container citrus. One of the biggest plus’s for container grown plants is being able to roll them (plant container rests on a wooden, plastic or metal base with wheels) to shelter when adverse weather conditions prevail. The size of the container is the most limiting factor. The size should be larger enough to permit maximum growth, yet small enough to be readily moved during freezing weather.
This information is taken from the Extension publication, “Home Fruit Production-Citrus,” written by Julian W. Sauls, Extension Horticulturist in Weslaco. To request a copy by mail call the Extension office at 210/467-6575. You may access the entire booklet online at http://aggie-horticulture.tamu.edu/extension/homefruit/citrus/citrus.html.
This article was submitted by Lynn Rawe, County Horticulture Agent with Texas Cooperative Extension in Bexar County.