Got Nature? Blog

Purdue Landscape Report: Stop me if you’ve heard this one…. A tree is in a slow decline year after year. You are called to your client’s property only to find the root flare well below grade.

Most professionals in the Green Industry have encountered this at some point in their career. The most common reason for the slow decline of trees in the landscape is due to the depth of planting and girdling roots. Deep planting can cause a number of deleterious problems, including an increase in circling/girdling roots restricting vascular tissue and decay of protective bark (Fig. 1). The vascular tissue in the bark is located on the outer portions of the trunk, while the anatomy of roots contains the vascular tissue in the center. This is why roots can graft with roots and stems can graft with stems, but also why roots can girdle the stems of trees (Fig. 2)

Figure 1. A tree that’s planted too deep can have bark decay from too much soil moisture around the trunk.

Figure 2. Root girdling can occur on trees that didn’t have a root correction during transplanting and/or being planted too deep. Restriction of vascular tissue in the trunk will decrease the amount of water and nutrients taken up by the tree.

Excessive mounding of mulch (aka volcano mulch) (Fig. 3) can contribute to tree decline, very similar to a tree planted too deep. It’s important to remember that keeping mulch several inches away from the trunk is imperative in tree health.

If a newly transplanted tree is planted significantly too deep, a faster decline can occur, especially in plants that can’t tolerate ‘wet feet’ (aka too much soil moisture) (Fig.4). In heavy-clay soils, the negative effects on tree health increase by creating a bath-tub situation by water not draining expeditiously after a rainfall or irrigation event.

Figure 3. Volcano mulch can cause the same problems that a tree planted too deep can experience.

Figure 4. Decline of this juniper is caused by this tree being planted too deep.