University of Florida/IFAS Extension Director for Nassau County, Rebecca Jordi, answers questions, provides expertise and tips about landscaping and gardening in northeast Florida.
Garden Talk Q & A
QUESTION: I added about 12 inches of soil around my house and on top of my trees. I lost several pine trees within a few days. Is the soil the problem? How could soil on top of tree roots kill the trees? RB
JORDI: You are the second person to ask me this question, so it makes sense to let the public know how important it is to avoid adding soil to the top of tree roots. Even adding a few inches of soil on top of roots can inhibit the air available to the roots and cause tree decline.
The best solution, one improving the health of the tree, is to remove lawn grass as far as possible from around the tree roots along with the additional soil you added. The potential of these trees becoming risk trees is becoming greater by the day.
How To Mulch Trees
Apply a thin layer of pine bark or pine straw as mulch. This mulch should be no more than 2-3 inches deep. Do not pile it up against the tree trunk, but allow an area of 8-12 inches directly around the tree with nothing but soil and air. Ideally, mulch the area totally under the tree branches.
Shrubs or ground covers could be planted before mulch is applied but nothing within an area of 3x the diameter of the tree trunk. Remember, the tree will get bigger – allow for future growth.
Take great care not to cut many roots when planting under the canopy. Roots greater than half an inch diameter should not be cut when planting under the tree.
Soil can be added to cover exposed roots but only 1 inch to slightly cover the roots. The soil added should be of a coarser texture than the existing site soil. This will allow roots to grow because air and water can easily penetrate to the existing soil. When soil of a finer texture is added, water and air penetrate with difficulty and tree health can decline.
Spread Soil By Hand
Operating soil spreading equipment over the roots will compact the soil and can damage roots. Spread soil by hand to eliminate compaction and root damage under the canopy. Do not add weed cloth around the roots of trees or shrubs as this can compact the soil and cause additional problems.
Rebecca L. Jordi
Nassau County Extension Director
UF/IFAS Environmental Horticulture
543350 U.S. Highway #1
Callahan, FL 32011