Texas is an enormous state with vast climate differences. According to the USDA plant hardiness zone map Texas's zones range from 6a to 9b, with South Texas being in the range of 8 and 9. For fruit growers this means that South Texas is a desert and has excellent growing conditions for tropical fruit such as citrus.
Test the soil of your yard for both its pH and soil type. Most tropical plants including citrus and avocados, prefer acidic soil, so the soil should have a pH of roughly 5.0 to 7.0.
Fix the soil. South Texas contains primarily clay soil, which while nutrient dense also has poor drainage. Poor drainage can lead to root rot. Dig a hole roughly six feet in diameter and four feet deep and mix one part peat moss, one part coarse sand and one part dirt from the hole. Fill the the hole with this mixture.
Fertilize twice each year with slow release fertilizer. Citrus and avocado are heavy feeders, so proper fertilizing is essential to healthy foliage and large fruit production. Read the label of the fertilizer carefully before applying it to your fruit tree and apply only the recommended amount.
Deep water the fruit trees regularly. Fill your tree's well completely and allow the water to drain into the soil. Repeat this process once more for a deep watering. Deep watering encourages the tree's root system to spread out deep into the soil and ensures that the top of the soil dries out completely to prevent disease. Water you tree whenever the top soil becomes dry to a depth of two inches.