A mature avocado tree needs to have at least two pounds of nitrogen a year and varying amounts of other nutrients, such as phosphorus and zinc. For the home gardener, the easiest way to feed your avocado is to use a mixed fertilizer specifically recommended for citrus and avocados that contains nitrogen, phosphorus, potassium and zinc. Be sure to follow the package directions.
In coastal zones, gardeners should divide the amount of fertilizer for the year into five equal applications and give one feeding each month from February through June. Interior gardeners should divide the total amount into four monthly applications and give one feeding per month from March through June. With slow-release fertilizers you can divide the fertilizer into two equal doses. Give the first dose early this month if you live along the coast, or late this month if you live inland, and give the second dose in June.
If you choose to go with single-use fertilizers, you can feed avocados by spreading 25 pounds of aged chicken manure under each mature tree in February. Beginning in March, give each tree one trowelful each of blood meal and bone meal every six weeks, through August. If the mulch is very thick, rake it off, sprinkle the food underneath, then replace the mulch on top.
The main things an avocado desires are rich soil, excellent drainage, and a thick layer of mulch over the roots. Allow the leaves that fall to remain under the tree; don't rake them up. (Avocados are best planted at the back of the garden where their large leaves won't look too messy.) Add additional mulch to young trees.
Remember, never cultivate or dig under avocado trees, because that would damage the roots and all your fruit might fall off. It's best not to grow anything under an avocado tree, especially if that something needs frequent irrigation. Wet soil promotes root rot of avocado.
Click here for liquid fertilizer rates and here for dry fertilizer rates.
Click here for avocado irrigation rates.