Question
Hi Jim, I have 3 huge Junipers in front of my house.  They are literally trees growing out of my flower beds.  I love them, but their roots make it nearly impossible to plant flowers in the beds.  I'd like to build up the flower beds a foot or two with retaining block.  Would 1-2 feet of dirt around the trunks of the Junipers hurt them?  Also, each Juniper has at least one limb that the previous owner cut back to a foot from the trunk.  Would it hurt the trees if (in the fall) I trimmed these limbs all the way to the trunk?  I live in Minneapolis, MN.  Thanks, Jim!

Answer
Yes adding 12-24 inches of soil to the root area of the trees will cause them to start dying back. Should never add more then 4 inches of soil to the root zone of trees. The added soil will compact the air pockets and smother the roots.

One of the biggest killers of urban trees is soil compaction. Soil compaction restricts water and oxygen uptake by roots, and is associated with roads, parking lots, foot traffic, construction machinery, livestock, poor soil preparation, and a host of other factors.

Changes in soil depth around trees also can cause injury to root systems. The addition of only 4 to 6 inches of soil over a root zone drastically reduces the amount of oxygen and water available to the roots

Quick Facts...

Figure 1: Area root distribution vs. crown distribution.  
Most tree roots are located in the top 6 to 24 inches of the soil and occupy an area two to four times the diameter of the tree crown.
Roots obtain water, oxygen and minerals from soil. They do not grow toward anything or in any particular direction.
Soil compaction, change in soil depth and improper watering can injure roots, increasing stress and susceptibility to disease and Insects.
To avoid root disease, maintain a healthy, vigorous environment around a tree. Once a root system is severely affected, the tree usually must be

Pruning limbs back to the trunk is the preferrred method fpr pruning--this will not harm the tree and make it look better. .