Will an arborvitae grow over the stump of another arborvitae?
I have two 12 foot high arborvitaes, each of which is growing in a brick planter. I want to replace them with two others that will grow no taller than 6 feet or 8 feet high. Although I can saw the existing arborvitaes down with a chain saw, I am not sure that I will be able to completely remove the stumps. I have uncovered the top of the root ball of one of the arborvitaes and it measures 17 inches in diameter. Since the Arborvitaes are in planters, the roots have grown down instead of out and will be very deep. Moreover, the branch roots that grow out of the root ball measure about 2 inches in diameter. I think that I will be able to uncover each of the top branches and cut them with a chain saw and then saw through the top of the root ball or chop through the top of the root ball with a hatchet. This will remove the top of the ball but the rest will remain in the ground. I estimate that I could cover the remaining portion with 6 inches - 8 inches of dirt. If I plant another lower growing arborvitae on the same spot, the bottom part of its root ball probably will almost touch the remaining stump. However, arborvitae is a very slow growing plant and the stump should decay as the new arborvitae grows. If I do this, will the new arborvitae grow or must the stump be completely removed?
It will take years for the old stump to decay. If you leave the stump, the new arborvitae will not be able to establish its root system, drainage will be affected, and the tree will not be healthy. It is best to remove the old stump before planting a new tree.