Ask an Arborist: Why is Volcano Mulching Bad for Trees and What Are the Benefits of Removing the Excess Mulch?

Trees are the backbone of our ecosystem and landscape. However, certain practices, such as volcano mulching, can significantly threaten their health. This blog explains why volcano mulching is detrimental to trees and explores the benefits of removing excess mulch. Additionally, we delve into issues like girdling roots and effective soil amendment techniques to ensure the vitality of your trees.

Understanding Volcano Mulching

The Dangers of Volcano Mulching

Volcano mulching is the practice of piling mulch in a mound around the base of a tree, resembling a volcano. Although it might look neat and tidy, it poses severe risks to tree health.

1. Oxygen deprivation: Piling mulch too high around the trunk can suffocate the roots, preventing them from receiving necessary oxygen.
2. Root and trunk rot: Excessive mulch, especially when it is in direct contact with the trunk, can retain moisture against the bark, leading to rot.
3. Girdling roots: Poor mulching techniques encourage the development of girdling roots, which can choke the tree over time.

Fixing Girdling Roots

Girdling roots grow around the base of a tree, restricting the flow of water and nutrients. Correcting this involves using an air spade to expose the roots carefully and then performing targeted root pruning. Approximately 20-30 percent of the root system can be pruned per visit, ideally in the spring or fall. This process could take up to three years for full correction, depending on the severity.

The Benefits of Removing Excess Mulch

Removing excess mulch from around your trees has several benefits.

1. Enhanced oxygenation: Reducing mulch allows the roots to access more oxygen, which is critical for their health.
2. Prevention of rot: By ensuring that mulch isn’t directly touching the trunk, you can prevent issues like root and trunk rot.
3. Reduction of girdling roots: Proper mulching techniques can reduce the likelihood of girdling roots from forming.

Alternative Mulching Methods

Vertical Mulching

Vertical mulching is a beneficial technique for trees. This process involves digging narrow trenches within the tree’s critical root zone and filling them with materials such as sand, gravel, biochar, perlite, compost, fertilizers or mulch. The benefits include:

1. Improved soil oxygenation: Trenching enhances air penetration into the soil, supporting root health.
2. Encouraging beneficial biological activity: The materials used in vertical mulching promote healthy soil microorganisms and worms, which further support tree health.
3. Enhanced water infiltration and soil structure: Vertical mulching can improve water absorption and drainage, preventing waterlogging and reducing soil compaction.
4. Convenient fertilizer delivery: By filling the trenches with compost or specific fertilizers, nutrients are delivered directly to the root zone, promoting better uptake by the tree.
5. Reduction in surface erosion: The trenches help stabilize the ground and reduce erosion around the tree, particularly on slopes or uneven terrain.

Soil Amendment Techniques

Healthy soil is the cornerstone of a healthy tree. Arborists commonly use air knives to decompact the soil within the drip line of the tree to depths of 8-12 inches. Depending on soil tests, substances like sulfur, compost, manure, worm castings, biochar and kelp may be added. The ultimate goal is to enhance soil structure and fertility, ensuring robust tree growth.

Conclusion

Understanding the detrimental effects of volcano mulching and taking proactive steps to remove excess mulch can significantly improve tree health. By addressing girdling roots, employing beneficial mulching techniques like vertical mulching, and implementing effective soil amendment strategies, you contribute to the longevity and vitality of your trees and the environment.

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