Planting Trees in Clay Soil: The "Bowl Effect" Debate

A certified arborist questions the advice to backfill with good topsoil, noting that in clay this creates a "bathtub" that drowns roots. They advocate using only native soil.

Nuanced Approach

In heavy clay, roughen the hole sides to prevent glazing. Amending the backfill with potting soil or compost (mixed with native clay) improves structure and drainage. Pure clay backfill can compact into a dense mass. The key is avoiding a smooth-walled hole and ensuring water can percolate laterally. Local conditions dictate the best method.