Understanding Roots in Restricted Areas

People love trees. I get lost of questions about placement of trees from people with special areas that they want to landscape. I have seen trees planted over underground parking garages, in rooftop gardens, in sidewalks downtown, and just about any other location where you can plant, including containers for indoor enjoyment.

The standard rule on planting a tree is to consider the ultimate size of the tree, avoiding areas under power lines, for example. In addition to considering tree height, we must also bear in mind the potential size of the root system when selecting trees and locations for planting them.

Roots must function properly for the normal above ground processes, like growth, to happen. If roots are restricted too much, improper nutrient and water absorption will limit the benefits of photosynthesis, preventing healthy plant growth.

We place trees in certain locations because we are looking for the tree to do a specific job. We expect color, shape, size, shade, maybe space definition; perhaps we're anticipating windbreak or other more functional benefits. We need to consider not only the full-grown top of the tree and how that will impact the surrounding area, we need to also understand the root system and provide for the plant as much as we can.

Roots anchor the plant, absorb water and nutrients, and continue to grow as late as Christmas even when the top of the tree might seem dormant. Fertilizing the plant is important and should be done twice each year: in the spring and in the late fall.

Remember, too, that trees eventually die. Their life expectancy may be longer than ours-150 years or more, in some cases-but eventually they will die. We want to get the most out of the tree for as long as we can by providing for the roots; at the same time, we want the tree to do the job without destroying any other needed facilities such as sidewalks, driveways or even foundations.

The best way to do this is to carefully consider the amount of limited space that exists in areas in which you are planning to plant trees. If you are looking at the space between the curb and the sidewalk, for example, measure the distance. If it's less than 3 feet, do not plant a tree there. For a width of about 3 to 5 feet, consider a small ornamental or flowering tree. From 5 to 6 feet you can consider a small shade tree. If you have more than 6 feet, you can pick about any tree, but try to avoid the forest giants. Trees near you house should be planted at least 15 feet away to avoid damage to the foundation, and a greater distance is better.

In cases in which you want a tree to do a specific job, bear in mind that trees have an expected service life based on where they are growing and the conditions in that spot. Given three identical trees that were started in the same nursery and then transplanted: one planted between sidewalk and curb will live 15-25 years, one planted in your lawn will live 40-75 years, but one planted in a large space and in ideal natural conditions will live 150 years or more.

If root restriction is unavoidable, consider the ultimate size of the tree, both the root zone and the top that can be tolerated in your circumstances. You may want to rethink your plans when you realize that properly selected trees will extend the life of your landscape. If you have trees that have reached the end of their service life and are being destructive, let's not hesitate to make new selections and start over again.