Certified Professional Horticulturist (CPH) Practice Exam

A protective measure for in-ground ornamentals is the use of pine bark, compost, fir bark, or pine needle mulch. What is the recommended depth to which the mulch should be applied?

1. 7"- 8"

2. 5"- 6"

3. 1"- 2"

4. 3"- 4"

The correct answer is: 1"- 2"

The correct depth for applying mulch around in-ground ornamentals is typically between 1 to 2 inches. This depth is sufficient to provide a range of benefits, including moisture retention, temperature regulation, and suppression of weed growth, without creating an overly thick barrier that can lead to issues such as poor air circulation or the potential for rot in the plant stems. Applying mulch too thickly can prevent water and nutrients from penetrating the soil effectively, which can adversely affect plant health. The 1 to 2 inch depth strikes a balance by ensuring that the mulch is effective while not overwhelming the plants. It's also important to keep the mulch away from direct contact with plant stems and trunks to avoid moisture retention close to the plant, which can lead to fungal diseases.