Certified Professional Horticulturist (CPH) Practice Exam

How deep should the mulch be around plants for optimal growth?

1. No more than one inch

2. No less than one inch

3. No more than two inches

4. No less than four inches

The correct answer is: No more than two inches

Mulch plays a vital role in promoting optimal growth for plants, and the recommended depth is typically no more than two inches. This amount is ideal because it effectively conserves soil moisture, suppresses weed growth, and regulates soil temperature without creating issues such as reduced oxygen availability or creating a barrier that prevents water from reaching the soil. When mulch is applied at a depth greater than two inches, it can lead to water not penetrating effectively through the mulch layer, which can dry out the underlying soil. Additionally, too much mulch can create an environment that encourages rot in plant stems and roots due to moisture retention too close to the plants. Conversely, maintaining mulch at one inch may not provide sufficient coverage to achieve all its benefits, and going below this depth reduces the effectiveness of weed suppression and moisture retention. Ultimately, a two-inch depth strikes a balance that maximizes the advantages of mulching for plant health and growth.