April 14, 2024

Extending the life of urban trees

Many urban trees only live about 20% of their life due to issues like pests and disease, but mostly can be linked back to improper care and installation. Quite simply, a tree should live more than 50 years and up to 100 years, depending on the species.

A recent U.S. Department of Agriculture study analyzing tree life expectancy in urban areas averaged the typical street tree living between 19 to 28 years.

However, the ideal lifespan of a white oak is 600 years and the average lifespan of a red maple can be between 75 to 150 years in the Illinois wilds.

Urban greening through planting trees has increased in response to residents’ lack of interaction with nature and the benefits these trees provide the environment through services like cooling buildings through shade and cleaning the air and water through filtration.

However, urban trees must withstand pollution, poor soils, limited leg room for roots and pressure from insects and disease and their health and cultural requirements are not considered or monitored.

Maybe it’s these urban challenges that cause them to die young. What’s worse, most are planted incorrectly, giving them a poor outlook from the beginning.

However, some basic knowledge of tree planting can help your urban tree live longer.

Right Tree, Right Place

It is essential that certain growing parameters be considered when choosing what kind of tree to plant. Answer the following questions to choose the right tree.

How much space does the tree require in its maturity? What are the attractive characteristics? Is the tree deciduous or evergreen?

What are the cultural requirements of the tree — sunshine, soil, water and climate? What is the soil pH and the soil type — well drained or compact?

Does the site get full sun or partial sun? How much water does that tree need? What is the growth rate of the tree? What kinds of things does the tree tolerate — salt, drought, flooding?

What are the insect and disease issues that tree faces? What are the planting needs and pruning needs of the tree? Can the tree thrive in areas that restrict root growth?

Trees Planted Too Deep

Trees planted too deep look like telephone poles because their natural root flare cannot be seen above the soil line. This strangles the roots below the soil.

A proper planting hole is two to three times wider than the root ball and no deeper. Rough up the sides of the hole with your shovel so roots will spread easier.

Place the tree so the root flare is at or just above the soil line. Sometimes, the tree is planted too deep in the container or root ball it comes in.

It is essential that you dig a little to find the top root, and plant at that depth. Amending soil may have good results in the beginning, but ultimately cause roots not to expand and may cause issues with watering.

Trees Improperly Pruned

Many say the worst and best thing for a tree in an urban environment is pruning. The worst is derived from improper pruning practices.

Topped trees to stubbed branches cause the tree to grow weak branches and create a potential avenue for insect and disease issues. Proper pruning allows good structural growth, protection from wind and reduces the risk of tree failure.

The reason urban trees need to be pruned versus forest trees is they grow massive side branches that are usually shaded out in a forest environment. Learn the basics of tree pruning and start corrective pruning the second season of your tree’s life.

Improper Mulching

In the industry, we say mulch like a bagel and not like a muffin. Never allow mulch to contact the trunk of the tree. Use organic mulch like such as hardwoods or cypress.

Extend the mulch ring 2 to 4 inches deep as far out as you are willing to go. Properly mulched trees will require fewer irrigations, less competition with grass roots and keep trees safe from lawn mower damage.

Kelly Allsup is a University of Illinois Extension horticulture educator.