Within the United States, avocado trees (Persea americana) are grown predominately in California, Florida, Hawaii, Puerto Rico and Texas, but they can also be grown in Louisiana. They thrive in warm, humid climates and are generally hardy in U.S. Department of Agriculture plant hardiness zones 8b to 11. Mexican varieties are suitable for central Louisiana, while Indian and Guatemalan varieties can be grown successfully in southern Louisiana in USDA zones 9 and 10.
Select a planting site where the avocado trees will be exposed to at least six hours of direct sunlight each day. Choose a slightly elevated area, if possible, where the soil drains quickly. Avocado trees will not thrive in soil that drains slowly. Build up a 2- to 4-foot-high, 4- to 6-foot-wide soil mound for each tree if the water table is not at least 3 feet below the surface. Plant the trees in native soil and do not amend the backfill soil. Choose an area where the trees can be planted at least 23 to 30 feet away from each other, other trees and your house or other structures.
Pour 2 to 3 gallons of water over the avocado rootball avery other morning for the first month after planting. Poke a finger into the soil near the rootball to check the moisture level at a depth of 6 inches. Wait another day or two to water if the soil and rootball are dripping wet. After the first month of growth, apply 6 to 7 gallons of water to each tree for the next three years. From the fourth year on, supply 6 to 7 gallons per 10 feet of tree canopy every 10 days to two weeks when it does not rain.
Give the avocado tree nitrogen-phosphorus-potash-magnesium fertilizer beginning in the spring after it begins putting on new leaves and growth if it was planted in the fall or one to two months after planting if it is planted in the spring. Fertilize the tree every one to two months during the first year. Spread 1/4-pound of 6-6-6-2 fertilizer over the root zone and water it into the soil. Increase the amount to 1/2 pound of fertilizer per application by the end of the first year.
Fertilize the tree six times per year during the second and third year and four times per year thereafter. Give the tree 1/2 pound of fertilizer at the beginning of the second year and increase the amount to 1 pound by the end of the year. Go from 1 pound of fertilizer at the beginning of the third year to 1-1/2 pounds by the end. Give the tree 1-1/2 pounds at the beginning of the fourth year and increase it to 2-1/2 pounds by the end of the year. Continue increasing fertilizer application rates in this manner until the eighth year. Give the tree 5 pounds of fertilizer each time from the end of the eighth year on. Change the fertilizer to one with a ratio of 8-3-9-2 when it begins bearing fruit.
Test the soil pH. Avocado trees commonly develop iron deficiency or chlorosis when planted in alkaline soil with a pH above 7. Give the tree three to four iron chelate soil drenches over the spring and summer if the soil pH is above 7. Dilute the iron chelate at a rate of 1 teaspoon to 2 gallons of water, or at the manufacturer's recommended rate. Pour the solution into a sprayer and spray it evenly over the soil around the tree. Wash the solution off the leaves. Give the tree 2 gallons of solution at the beginning of the first year and increase it to 3 gallons by the end of the year. Apply 3 to 4 gallons of solution the second year, 4 to 6 gallons the third year and 6 to 8 gallons the fourth year. Give the tree 8 to 16 gallons of solution from the fifth year on.