My Tree Has Bad Soil – How To Improve Soil Around An Established Tree

Rocks And Mulch Surrounding A Planted Tree
tree soil
(Image credit: Jummie)

When trees aren’t thriving in a backyard, homeowners – and even some arborists – tend to focus their attention on the cultural care the tree is getting and pest or disease issues. The vital role the soil plays in a tree’s health can easily be overlooked.

When a tree has bad soil, it cannot establish roots and grow well. That means that improving soil around trees can be the most important part of tree care. Read on for information about the effects of compacted soil around trees and tips on how to improve the soil around an established tree.

If Your Tree Has Bad Soil

A tree’s roots uptake water and nutrients that allow the tree to produce energy and grow. Most of a tree’s absorptive roots are in the topsoil, to a depth of about 12 inches (30.5 cm.). Depending on the tree species, its roots can extend far beyond the tree canopy dripline.

If a tree has bad soil, that is, soil that is not conducive to root growth, it won’t be able to function. One particular problem for urban trees is compacted soil around trees. Soil compaction has a very negative impact on the health of trees, stunting or preventing growth and leading to pest damage or diseases.

Construction work is the number one cause of soil compaction. Heavy equipment, vehicular traffic, and excessive foot traffic can press down the soil, especially when it is clay-based. In compacted clay soil, the fine soil particles get tightly packed. The dense soil structure prevents root growth and limits air and water flow.

How to Improve Soil Around an Established Tree

It is easier to avoid soil compaction from construction work than it is to correct it. Using thick, organic mulch over root zones can protect a tree from foot traffic. The thoughtful design of a worksite can direct traffic away from established trees and make sure that the root zone is not disturbed.

However, improving compacted soil around an established tree is another matter. For treatments to be effective, you have to address all of the problems that compaction causes: soil too dense to allow roots to penetrate, soil that does not hold water or allow it to enter, and poor quality soil without many nutrients.

If you are wondering how to improve the soil around an established tree, you are not alone. Many arborists have come up with techniques to treat compacted soil, but few of these are effective.

Two simple things you can do to start improving soil around trees are mulching and irrigation:

  • Apply a 2- to 4-inch (5-10 cm.) layer of organic mulch a few inches (7.5 cm.) from the trunk to the drip line and reapply as necessary. The mulch immediately conserves soil moisture. Over time, mulch protects against further compaction and enriches the soil with organic matter.
  • Proper amounts of irrigation are essential to a tree’s development but hard to determine when the soil is compacted. Use a moisture sensing device and an irrigation system to provide optimum moisture without the risk of excessive irrigation.
Teo Spengler

Teo Spengler has been gardening for 30 years. She is a docent at the San Francisco Botanical Garden. Her passion is trees, 250 of which she has planted on her land in France.