Certified Professional Horticulturist (CPH) Practice Exam

How often should well-established trees generally be fertilized?

1. Every 6 months to a year

2. Year to year and a half

3. Two to four years

4. Three to five years

The correct answer is: Three to five years

Well-established trees generally require less frequent fertilization compared to younger or newly planted trees. The correct choice indicates that a fertilization schedule of every three to five years is sufficient for these mature trees. This is because, as trees age, their root systems become more extensive and efficient at foraging for nutrients in the surrounding soil. Additionally, well-established trees often have developed a balanced ecosystem in the soil, containing beneficial microorganisms that contribute to nutrient uptake. Regular, frequent fertilization can disrupt this natural balance, potentially leading to nutrient runoff and environmental concerns. Choosing to fertilize every three to five years allows for the addition of nutrients in a manner that supports the tree's health without overwhelming the system, thus promoting sustainable growth and minimizing environmental impact. In contrast, more frequent fertilization intervals, such as every six months or annually, may not provide additional benefits and could even be counterproductive, creating nutrient imbalances and affecting soil quality over time.