Certified Professional Horticulturist (CPH) Practice Exam

Based on the optimum growth needs of vegetable plants, which soil pH range is recommended?

1. 7.0-7.3

2. 6.3-6.5

3. 5.7-6.0

4. 5.0-5.5

The correct answer is: 6.3-6.5

The recommended soil pH range for optimum growth of vegetable plants is typically between 6.3 and 6.5. This pH range is slightly acidic, which is ideal because it allows for the best availability of nutrients essential for plant growth. Most vegetable crops thrive in this pH level, as it optimally balances nutrient solubility and microbial activity in the soil. At this pH range, nutrients such as nitrogen, phosphorus, and potassium—as well as micronutrients like iron and manganese—are readily available to plants. When the pH is within this range, it also encourages beneficial soil organisms that help with nutrient cycling and organic matter decomposition, further supporting plant health. Soils that are too alkaline (above 7.3) can lead to nutrient deficiencies, particularly with micronutrients that become less available. Acidic soils (below 6.3) can also lead to problems, including potential toxicity of certain elements and decreased nutrient absorption. Therefore, maintaining a soil pH between 6.3 and 6.5 creates a favorable environment for vegetable growth.