Oklahoma is a Midwestern state that falls in USDA hardiness zones 7 and 6. Winter lows in Oklahoma can dip as low as -10 degrees. Because of this, avocado trees will not grow well in Oklahoma. Avocados are a tropical and subtropical tree that will not tolerate frost. In order to grow an avocado tree in Oklahoma, you must grow the plant in a container so that it can be moved indoors in winter.
Purchase a grafted tree from a nursery to find a variety that will produce fruit within a few years. Trees grown from seeds are hybrid seeds. The trees they produce will not grow into trees that are like their parent tree and will not produce fruit for up to 15 years. Varieties that will do well in Oklahoma include Mexicola and Mexicola Grande.
Select a potting soil that is well-drained. Or mix your own using 1 part sand, 1 part peat moss and 1 part compost.
Choose a container that is only 2 inches larger than the root ball of your grafted tree seedling. Trees planted in larger containers will have spindly trunks.
Fill your container 1/3 full with soil and place the plant in the container. Fill in the sides of the container with potting soil. Then cover the root ball slightly with soil.
Water the plant with water and a liquid balanced (10-10-10) fertilizer according to the package directions. All fertilizers are different, so each fertilizer will have specific directions for that brand. Your soil should remain as damp as a wrung-out sponge.
Place the container in a window with full sunlight or under grow lights in winter. Move the plant outdoors so that it receives full sunlight in spring.