Avocado trees prefer a warm tropical climate but can be grown in subtropical areas with good cold protection. The more cold-hardy Mexican avocado varieties of Opal, Wilma, Fantastic Avocado, and Joey Avocado and Poncho are best suited to the Houston climate, according to Urban Harvest. Avocado trees need to be protected from the Texas sun and occasional freezing weather during the first few years, but after that they should need little care.
Choose a well-drained location with plenty of sun and protection from wind if possible.
Remove grass and weeds from the area. Supplement the clay soils found in most of Houston with organic materials to loosen the soil and improve drainage. In poorly draining areas, plant the tree on a mound or raised bed.
Dig a large, wide hole, at least 3 to 4 times the size of the original container.
Remove the tree from its container, and place it in the hole at the level it originally grew. Backfill the hole with the amended soil, tamping it down around the tree.
Water under the tree after planting, and continue watering daily during the first 7 days. Water the avocado tree twice a week for the first few months, and weekly during dry weather.
Pile soil around the trunk to protect young trees from cold weather. Cover them loosely with a blanket or tarp whenever freezing weather is expected. During severe freezes or extended cold weather, add a heat source, such as a light under the tarp.
Protect avocado trees from the brutal Houston sun during the first two years. Paint the trunk with a whitewash made from diluted latex paint or erect cage of shade cloth to shade the lower part of the tree.
Use a balanced fertilizer and a nutritional spray 3 or 4 times a year. Apply iron chelates in late spring and summer in areas with alkaline soils.
Harvest avocados when the fruit is large and mature. Pick one and allow it to ripen at room temperature. If it turns rubbery, the avocados are not yet ready to harvest; wait until one successfully ripens before beginning to harvest. Pick the larger avocados first, stretching out the harvest over the season. Fruit that you don't pick may fall off the tree at the end of the season.