Certified Professional Horticulturist (CPH) Practice Exam

When planting a plant, how much larger than the root ball should the diameter of the hole be?

1. 10-20% larger

2. 25-50% larger

3. 60-75% larger

4. 80-100% larger

The correct answer is: 25-50% larger

The recommended practice is to have the diameter of the hole be 25-50% larger than the root ball when planting a plant. This ensures that the plant has sufficient space for its roots to spread out and establish themselves in the new environment. A hole that is larger allows for better drainage and aeration, which are critical for healthy root development. This extra space helps the roots to penetrate the surrounding soil more easily, improving the plant's ability to access nutrients and water. Furthermore, when the hole is adequately sized, it reduces the risk of "root girdling," where roots may circle around too tightly if the hole is too small. Options that suggest a diameter significantly larger than 50% may create excessive space, which can lead to settling and instability for the plant once it's established. Conversely, a hole that is only 10-20% larger is generally insufficient to accommodate the roots effectively, which could hinder the plant's growth. Therefore, choosing a hole that is 25-50% larger strikes the best balance for promoting healthy root growth and stability of the plant.