Citrus is relatively simple to grow in south Texas thanks to the infrequency of freezes and long growing season. Citrus are tropical trees, and have few cold-protection mechanisms. But citrus planted in fertile soil with ample sun can grow in almost any region of Texas, so long as they are protected during the winter. In central and north Texas, limit the size and number of citrus trees you care for to make overwinter care more manageable.
Ensure the site of the orange tree has good drainage and a plentiful source of compost. Maintain a 2-inch layer of well-rotted compost throughout the growing season to conserve moisture, leech nutrients into the soil and prevent weeds. Leave a ring around the trunk of the tree about a foot in diameter free of compost, weeds or mulch to prevent foot fungus disease.
Remove all weeds and grass around the tree all the way out to the canopy line by hand or with a hoe. A few sparse plantings under the tree with small, non-aggressive root systems and very low water and nutrient requirements are fine. The important thing is to keep the citrus tree from having to compete for water and nutrients, especially when it is trying to set blooms and fruit.
Trim back neighboring trees with sharp loppers or a pole saw if they shade the citrus trees too deeply. Many citrus trees are understory trees and grow well in light shade, but won't produce as much fruit. A small amount of shade trees can be a good thing for citrus grown in Texas, to provide relief from heat or high winds.
Water deeply and infrequently. Numerous shallow, light waterings encourage the roots to develop in shallower soil, and never allows the tree to get a full drink. Considering the length and severity of summer heat and drought in many areas of Texas, it is better encourage the roots to grow deep into the soil to find water by watering slowly and allowing the water to seep deeply into the soil. Wait until the top 2 to 3 inches of soil are dry before watering again.
Cut back your watering schedule in cooler weather to prevent root rot. Water deeply before a predicted freeze. Wet soil does not change temperatures as rapidly as dry soil, and will protect the roots from freeze damage.
Use soil banks around young citrus trees in areas with prolonged freezes. Treat the trunk of the tree and the lower scaffolds with insecticide and copper-based fungicide. Gently mound soil borrowed from the garden, or potting soil, all the way up the trunk before the first freeze. Remove the bank carefully in March, rinsing all soil from the trunk and clearing the area over the root zone of excess soil.
Cover larger trees with sheets, blankets or plastic for short-term freezes. Place outdoor incandescent lamps under the coverings for added warmth. Turn them on before temperatures drop. Remove non-porous coverings on sunny days to prevent leaf damage.