Provide three applications of sulfate of ammonia, following directions on the bag. Water thoroughly after applying. Feeder roots, those sensitive to moisture excess or deprivation, are found in the upper 15 inches of the soil. Water the tree when the soil is dry three inches below the surface. Apply enough water to soak the soil 18 inches deep.
Avocados prefer an acid soil.
Applying soil sulfur, if needed, and sulfate of ammonia should keep the soil pH low enough. I started two avocado trees from pits. I've tried grafting and budding some limbs, but they don't take. Budwood is obtained from dormant terminal growth that is just starting to swell in the spring. Select only healthy, fat buds.