Persea Americana is cold tender and will only survive the winter in the southern tip of Texas. They can be grown easily from seed, but then a lot of people ask what to do with them. You have three choices: 1)build a tall greenhouse, 2)move to Brownsville, or 3)toss them in the compost pile and plant an adapted plant.
Avocado trees are tropical trees and are very sensitive to frost. If you are trying to grow one yourself, make sure it is brought in to a protected area whenever frost is a possibility.