Certified Professional Horticulturist (CPH) Practice Exam

What is the recommended thickness for applying mulch around in-ground ornamentals?

1. 7"- 8"

2. 5"- 6"

3. 1"- 2"

4. 3"- 4"

The correct answer is: 1"- 2"

When applying mulch around in-ground ornamentals, a thickness of 1 to 2 inches is generally recommended. This depth allows for several benefits that support plant health and garden aesthetics. Firstly, a layer of mulch at this thickness provides adequate moisture retention for the soil, helping to keep the root zone hydrated without causing issues such as excessive moisture that could lead to root rot. It allows for proper water penetration while minimizing evaporation. Additionally, a 1 to 2-inch layer of mulch helps suppress weeds effectively. Weeds can compete with your ornamentals for nutrients and water, and the recommended thickness hinders their growth by blocking sunlight while still allowing air circulation. This thickness also contributes to temperature regulation in the soil. It keeps the soil cooler in hot weather and warmer during the cooler months, which is beneficial for root development. Thicker layers can lead to issues such as smothering plant roots and creating a habitat for pests or diseases. Thus, maintaining a mulch depth of 1 to 2 inches strikes a balance between providing necessary benefits while avoiding potential problems associated with excessive mulch.