Fruit Tree Mounds, Rot & Poor Drainage

Root Rot

• The rotting of the root crown in fruit trees is caused primarily by species of the Phytophthora fungus. The presence of a reddish-brown coloration on the inner bark at the trunks' base, just below the soil surface, confirms the disease. On healthy trees, the bark should be white or tan. Some trees survive long periods with a low-level infection of root rot while others suddenly perish in one growing season.

Drainage Problems

• Constant soil saturation is the No. 1 factor that leads to root rot in fruit trees and hastens their pace of decline if the problem is allowed to continue. A low-lying site often has a naturally high water table and, without some form of mitigation, is not suitable for growing fruit trees. Excessive irrigation in heavy-clay soil is another common situation that leads to root rot. Some fruit trees, such as peach (Prunus persica) and other "stone fruit" trees, are far more susceptible to root rot than other species. Peach trees are hardy in U.S. Department of Agriculture plant hardiness zones 5 through 8.

Mounds

• Planting fruit trees on high ground is an established method to prevent root rot. If the crown of a tree's roots is just 4 or 5 inches above the surrounding soil level, then the incidence of root rot decreases dramatically. Planting mounds for fruit trees should be low and broad, and they should be made with topsoil from the planting site. For example, remove topsoil from a circular area around where you will plant a fruit tree, and mound that topsoil in the middle of the circular area. The excavated area creates a basin where water will drain instead of saturating the soil around the tree's crown. The bottom of the basin should be 8 to 10 feet from the tree's trunk.

Other Factors

• Additional factors can make fruit trees resistant or susceptible to root rot. When selecting trees for a poorly drained site, look for varieties grafted onto rootstock known to be rot-resistant and tolerant of heavy-clay soil and "wet feet," or wet roots. Incorporating copious quantities of organic matter into the soil prior to planting also buffers fruit trees from the effects of saturated soil. Also, avoid planting the trees too deep; each fruit tree's crown of roots should be just below the soil surface.