Facts on Avocado Tree Roots

Avocado trees produce a shallow, aggressive root system, making them susceptible to rot and infection from flooding and damage from surface activities. While many children have stuck toothpicks into avocado pits and set them in a jar of water to watch the roots emerge and grow, most commercial and landscape avocado trees are grown from grafts onto rootstock, not from seed.

Avocado trees produce the rich green fruit prevalent in Mexican cooking and prized for its oils. Native to warm, arid areas of North and South America, hardy varieties now grow in subtropical areas including California, Hawaii, Florida, the West Indies and the Mediterranean area, according to the California Rare Fruit Growers website. Dwarf varieties have been developed for container gardening.

Most of the avocado tree's feeder roots grow in the top 6 inches of soil, according to the University of California Agriculture and Natural Resources website. The roots grow outward from the tree trunk in all directions.

They prefer loose, well-draining soil and can tolerate acid or alkaline conditions, according to the California Rare Fruit Growers website. Avocado tree's highly competitive root system chokes out nearby plants that vie for water, air and nutrients. The strong, aggressive roots can buckle and break pavement as they grow.

The far-reaching dominant root system means avocado trees should be planted at least 30 feet away from buildings and other trees in landscape environments, according to the University of Florida extension service website.

The shallow nature of the root system makes the avocado tree susceptible to damage from flooding. If the roots stay wet, nutrients are lost and growth stunted. In prolonged flooding or saturated soil, the tree dies. Constantly wet soil also can lead to a root infection known as Phytophthora fungi, which reduces growth and fruit production, according to the University of Hawaii extension service website.

Commercial avocado trees start by grafting buds of mature trees onto seedlings or rootstock, according to the University of Hawaii extension service website. Fruit quality and yield vary widely among trees grown from seed and are more consistent from grafted trees.

Avocado trees produce fruit most abundantly when grown in full sun. They should be watered only during prolonged dry periods.

Trees grown from seed normally produce fruit five to eight years after planting, while grafted trees start bearing fruit in three to five years, according to the University of Hawaii extension service website.

Avocado tree seedlings or grafted trees from nurseries should be planted in a hole that is slightly wider than the root ball and covered with loose, loamy soil, according to the University of California Agriculture and Natural Resources website. Because the root system is sensitive to bumping, breaking and damage, the root ball should be slowly lowered into the hole without disturbing the roots.

Mulch mixed into the soil will promote drainage and aeration, but the mulch should be kept at least 6 inches away from the trunk.