Unlike anywhere in the US planting in Colorado is unique. Trees planted too deep tend to drown due to our clay soil. Deep planting causes rott at the soil line, which can eventually kill the plant. It usually takes a few seasons for a tree or shrub to die from this. Residents typically do not associate the decline of a tree with how it was planted.
Trees not planted deep enough will cause the critical parts of the root zone to die. When a tree or shrub is planted too shallow, or too far above grade, the roots that are supposed to grow horizontally have nowhere to go. They will stop at the edge of the root ball or completely die back to the main trunk.
Colorado’s soil causes additional problems with planting, besides being mostly clay it is not very rich in microbial activity. Colorado has minimal rain compared to eastern states which causes hi sodium content outside the planting hole. This means there is not as much of the deep dark topsoil as found in the east. Introducing mycorrhizae and bio stimulants when planting is a great way to encourage growth in newly planted material.
Based on years of experience the chart below is the proper way to plant in Colorado
2” diameter trees are the sweet spot!
When harvesting, they are able to get enough of the root zone to support the wood in a 2” diameter plant (or smaller). Larger trees tend to struggle and stress because when harvesting, they are unable to get enough of the fine fibrous roots that are necessary to support the amount of wood in a tree that is 3” in diameter or larger. They require a lot more attention and have a greater chance of mortality. At the very least they will struggle significantly to flourish.
Larger trees spend most of their energy after being planted, trying to generate a large enough root zone to support the tree adequately. Smaller trees thrive easier because the right root zone already exists. After planting a smaller tree, they are able to spend their energy growing because the root system is young, dense and resilient enough to be able to support the trees growth after planting.