San Antonio Express News
Sunday, January 16, 2005
This week Extension introduces the first of two articles sharing basic information on growing and caring for your own citrus trees. Most of the information is taken from an Extension publication, “Home Fruit Production-Citrus,” written by Julian W. Sauls, Extension Horticulturist in Weslaco, Texas. We will only give you a synopsis as the entire publication is too large to include here. You may access the entire booklet online at http://aggie-horticulture.tamu.edu/extension/homefruit/citrus/citrus.html or give us a call at 467-6575, and we will mail a copy to you.
Because of the strong possibility of freezes immediately ahead of us, today’s information will touch on caring for established citrus trees, and cold protection. Winter almost always will be accompanied by one or more freezes. Citrus trees are subtropical to tropical in nature; thus, they may suffer severe damage or even death because of freezing temperatures. The resident of coastal and southern Texas who is willing to put forth the effort to provide cold protection for young trees, and sometimes even mature trees, can successfully produce citrus fruits.
Commercial citrus production in Texas is mostly limited to the Lower Rio Grande Valley, however many Texas residents want citrus trees in the home landscape to enjoy their dark, evergreen foliage, fragrant blossoms and colorful, delicious fruit. A successful harvest is worth the effort.
Care of Established Citrus Trees
Cultural practices for established citrus trees are designed to maintain good growth and vigor to maximize the production of quality fruit. The common components of all cultural programs are irrigation, fertilization and weed and grass control. Pruning is rarely necessary, except at planting time and later to remove dead wood. Pest control may be necessary to produce bright, clean fruit, and occasionally to maintain tree health and vigor.
The homeowner commonly applies water too frequently and in inadequate amounts, resulting in inefficiency, waste and less than optimum growth and production. Water management is much more critical on poor soils than on deep soils. Most soils in southern Texas hold between 3 and 7 inches of water in the upper 3 feet of depth, with sandy soils at the low level and heavier clay soils at the upper level. This is the reservoir of soil moisture available to plants.
A good rule of thumb is one to two inches of water per week during the growing season. Since oxygen is needed in the soil in order for plants to take up the water, don’t saturate the soil. Also, the best roots are in the top four to six inches of the soil because this is where the greatest oxygen levels are. The effective root zone on most plants is only about 24 to 32 inches deep and if the soils are shallower – then it is less. This means once the water goes below two feet – it is much harder for the plant to use. So the trick is not to let the water run longer in a spot but rather to wet more soil volume. The poorer the soil is, the greater the volume of soil which needs to be wetted for maximum plant performance.
Southern Texas soils generally are quite fertile and contain more than adequate quantities of 13 essential elements except nitrogen. The other elements rarely need to be applied to mature, established citrus, however it is important that citrus receive adequate nitrogen. Clay soils usually contain plenty of iron, but citrus trees may exhibit iron deficiency in the early spring. Usually, the deficiency clears up as the soil warms up. If it does not, soil application of iron chelates is necessary. Where iron deficiency does occur, do not use fertilizers which contain phosphorous because high phosphorous aggravates iron and zinc deficiency in high pH (alkaline) soils. Red, sandy soils may need supplemental potassium and sandy soils in general may need additional zinc.
Mature, bearing citrus trees should receive enough nitrogen to provide for good but not excessive growth. If the percentage of nitrogen in the fertilizer is less than 15 percent, apply about 1 pound per inch of trunk diameter per year. If the percentage is above 20, use 0.75 pound or less per inch of trunk diameter per year. One pound of dry fertilizer is approximately 2 cups. The fertilizer may be applied at one time for the year, usually in February, or it may be split into two or three applications. Two applications are recommended, with two-thirds of the fertilizer applied in February and the balance in May. However, equal applications in February, May and September are also effective.
Weed and Grass Control
Weeds are serious competitors for both water and nutrients. It takes about 80 gallons of water to grow a pound of weeds. Performing a little weed control will eliminate the competition for water and greatly enhance tree growth. Try to keep the area around the tree weed-free to the drip line for the first 3 to 4 years of the life. Mulches are commonly used to conserve moisture and control weeds and grass. If used, keep mulches at least a foot away from the tree trunk.
Citrus trees are pruned primarily to control tree size and to remove dead, diseased or damaged wood. Established citrus trees should be allowed to grow naturally without pruning.
A Word About Cold Protection
Cold protection practices must be implemented to minimize the damage from a severe freeze. The duration of freezing temperatures is more critical than the minimum temperature, i.e., a brief drop to 24 degrees F may not cause as much damage as several hours at 26 degrees F. Exposure to cold weather increases the ability of citrus trees to withstand cold, as short days and cool weather condition the tree to stop growing and acquire greater cold-hardiness. Citrus trees in colder areas of southern Texas usually will attain greater cold-hardiness than those in the Valley. However, residents of freeze-prone areas should grow only cold-hardy types of citrus such as kumquats, satsuma mandarin, tangerines, and some tangelos.
The soil under and around the citrus tree should be bare and firm insofar as possible in a landscape setting. Remove mulches before winter. Thoroughly irrigate the citrus tree and surrounding areas several days before a hard freeze is anticipated. Bare ground can absorb more heat from the sun than can soil covered by weeds, grass or mulch. Moist soil can absorb more heat and conduct heat better than dry soil. Consequently, pre-freeze irrigated bare ground can absorb, store, conduct and release more heat to the tree during a freeze.
The tops of citrus trees may be draped with blankets, quilts or plastic for further protection. It is not necessary to encase the tree completely. Put such coverings on and anchor them securely the afternoon before the freeze. Remove plastic coverings during sunny days to prevent cooking the trees. Permeable covers can be left in place until freeze danger has ended.
A water sprinkler placed over the tree (without the other methods) can prevent freezing by covering the tree with ice. But, the sprinkler must be started before the temperature drops to the critical level – 28 degrees F on calm nights, 30 degrees F on windy nights – and must run continuously until the temperature is sufficiently above freezing that ice in the shade begins to melt. However, the ice load can cause significant limb breakage and a freeze lasting several days can result in excessive water-logging of the soil.
Despite your best efforts, freeze damage does occur to citrus trees. The immediate urge is to begin cutting off the deadwood, but there is no effective way to immediately determine the extent of deadwood. While it may be unsightly in the residential landscape, delay pruning until May. Citrus trees lose their leaves (and fruit) after a severe freeze, but they send out new growth in March. Much of this lush spring growth dies back in April because of underlying damage to the wood and bark. Consequently, delay pruning until after the dieback has occurred.
Next week we will focus on the selection of citrus varieties for our area, the planting and care for young trees and planting citrus trees in containers. In the meantime visit plantanswers.com and check out the Citrus information in the January newsletter, and also the Gardening Column Archives.
This article was submitted by Lynn Rawe, Horticulture Agent with Texas Cooperative Extension in Bexar County.