Will Covering the Exposed Roots of Magnolia Trees Do Damage?

Magnolia Root Systems

• While it may be easy to visualize, magnolia trees do not develop a root system that mirrors the above-ground trunk and branching structure. Magnolias do not have a singular, long carrotlike taproot, either. Magnolias develop shallow roots that rarely branch and look like long ropes that radiate out from the trunk. Since they grow shallowly, surface roots may reveal themselves atop the soil under the tree branches, creating tripping hazards or troublesome bumps and ridges for the lawn mower to traverse.

Root Needs

• Magnolias grow best in a soil that is porous, crumbly in texture, cool in summer and evenly moist. The roots dwell where nutrients, water and oxygen are most plentiful -- in the top 24 inches of soil. Surface roots develop when the soil is too moist or dense, or when trees simply become very old and large. Surface roots are more prone to stresses from drought, summer heat or trampling/soil compaction issues. Therefore, magnolias are best planted where the garden soil is irrigated, shaded and never compacted by vehicles or pedestrian traffic.

Covering Roots

• Surface roots radiating from the trunks of magnolia trees pose tripping hazards in the lawn or garden bed. However, attempting to remedy the situation by simply pouring soil atop the roots to create an even grade is a poor and unreliable solution. Placing soil atop a plant's root system changes the growing environment, especially regarding oxygen penetration to roots. Suffocating the tiniest roots leads to their death, and possible twig and leaf dieback on above-ground branches. The results of suffocating roots may not occur for months or years after soil is piled over the root system.

Insight

• Rather than burying magnolia roots under soil, place organic mulch over the root zone. Keeping turfgrass under a magnolia is an annoyance because of low branches and running over any surface roots. Kill the turfgrass and place a 3-inch layer of pine bark nuggets as mulch to cover the roots and even out the grade. The mulch is more porous than soil and does not compact to cause a lack of oxygen to roots. As the mulch decomposes, it provides nutrients to the magnolia. Replenish and maintain the 3-inch mulch layer so there's no need for mowing or weeding under the magnolia. The mulch also conserves soil moisture and shades the soil and roots, buffering the plant from droughts and excessive swings in temperatures.