Certified Professional Horticulturist (CPH) Practice Exam

A garden center customer claims that their plants do not seem to be growing well with purplish leaves. What is the best recommendation?

1. Add a complete fertilizer high in phosphorus

2. Have the plants' foliage and soil tested

3. Incorporate a high-quality compost around the plants

4. Add hydrated lime to release more essential nutrients

The correct answer is: Add a complete fertilizer high in phosphorus

The correct recommendation in this scenario is to have the plants' foliage and soil tested. When plants exhibit purplish leaves, it can indicate various issues, including nutrient deficiencies, particularly phosphorus deficiency, but also problems such as pH imbalances or environmental stressors. Testing the soil and foliage provides concrete data about the nutrient levels and other environmental factors affecting plant health, allowing for a targeted approach to remedy the specific problem. Adding a complete fertilizer high in phosphorus may seem beneficial since purplish leaves are often associated with phosphorus deficiency. However, without confirming that phosphorus is indeed the issue through testing, applying additional phosphorus could be unnecessary or even harmful, particularly if the problem lies elsewhere. Incorporating high-quality compost can improve soil fertility and health, but it doesn’t address the immediate need for understanding the underlying cause of the symptoms the plants are displaying. Similarly, adding hydrated lime is generally useful for adjusting soil pH, particularly in overly acidic soils. However, without knowing the current pH or the specific nutrient needs of the plants, this could also lead to further complications without first diagnosing the actual problem. Thus, starting with a soil and foliage test is the most appropriate step to accurately determine the issue affecting the plant growth and leaf coloration.