The world would be a sadder place without guacamole, the avocado-rich dip often enjoyed at parties. The semi-tropical avocado tree, which comes in many varieties, can reach 80 feet in height and serves as a pleasant and attractive shade tree. Avocados are native to Mexico, Central America and the West Indies. All types of avocado trees need fertilizer to grow large and strong and produce the largest number of fruits.
Types of Avocados
Three geographical "races" of avocado exist--Guatemalan, West Indian and Mexican. Avocados hailing from the Mexican race can tolerate cold better than fruit from the other two races. The West Indian types are more successful in tropical areas. Many varieties that are grown commercially have been hybridized from parent stock belonging to these races. "Haas" is a favorite avocado for its thick skin and smooth, buttery flesh. It comes from the Guatemalan strain. "Sharwil" is a cross between Guatemalan and Mexican races and is popular in Hawaii, where it accounts for almost 60 percent of commercially cultivated avocados.
Avocados and Citrus
Although avocados look and taste very different from oranges and other citrus fruits, both are classified as fruit, they prefer tropical or subtropical climates because they are sensitive to frost, and they have similar needs in terms of growing conditions and fertilizer. Some brands of commercial fertilizers are designed for both citrus and avocado trees. Both types of trees must grow in full sun with soil that drains well--neither type of tree can tolerate standing water.
You may need to amend the nutrients contained in the soil before you plant an avocado tree. Test your soil to determine the pH and the calcium content. Avocados need a pH ranging from 6.2 and 6.5--if it's not right, your avocado will not do well. You can raise the pH of acidic soil by adding calcium carbonate (lime). If you need to increase the magnesium content, substitute a bit of dolomite for part of the lime. To increase calcium in the soil, apply phosphorus fertilizer.
Fertilizer for Planting Time
Mix a balanced fertilizer into the avocado's planting hole before you set your tree into the ground. A plant food with an equal proportion of nitrogen, phosphorus and potassium is recommended. For example, fertilizer having an N-P-K ratio of 16-16-16 is the correct type. If you prefer, dig compost into the planting hole: For a bareroot tree in a 5-gallon pot or bag, mix two gallon-size buckets full of organic compost into the soil in the planting hole.
Ongoing Fertilizer Regimen
After an avocado tree begins to grow larger, broadcast granulated fertilizer with an N-P-K ratio of 10-30-10 around the tree's root zone twice a year, making sure to keep it at least one foot from the trunk. You can also apply liquid fertilizer through a drip irrigation system or as a foliar spray.
Compost and Natural Fertilizers
Avocado trees respond well to applications of compost, compost tea, worm castings and fish emulsion, which are all nonchemical fertilizers. Twice each year, spread a 3-inch-thick ring of compost around the tree's drip line. Trees also respond well to watering with compost tea or worm castings. If you mix up a batch of diluted fish emulsion according to package instructions and then water your avocado with it, this will provide many of the nutrients your tree needs.