ISA Certified Arborist Practice Exam

The primary purpose of applying mulch around trees is to retain moisture, suppress weeds, and enhance soil quality, which collectively contribute to the health and growth of the tree.

Mulch acts as a barrier, reducing evaporation from the soil and helping to maintain consistent moisture levels that are essential for tree roots, especially in dry periods. By limiting weed growth, mulch reduces competition for nutrients and water, allowing the tree to thrive without having to compete with other plants. Additionally, as mulch decomposes over time, it adds organic matter to the soil, improving soil structure, aeration, and nutrient availability. This natural process supports beneficial microorganisms and contributes to a healthier soil ecosystem that benefits the tree.

While attracting beneficial insects can be a secondary benefit of certain types of mulch, it is not the primary purpose. Mulch will not directly provide nutrients to the tree in the same way as fertilizers do, and while it can improve the appearance of a tree's planting area, aesthetic enhancement is not a foundational reason for its use.