Certified Professional Horticulturist (CPH) Practice Exam

What is the best recommendation to fix a nutrient deficiency when plants have purplish leaves?

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

When plants display purplish leaves, it is often an indication of a phosphorus deficiency. Phosphorus plays a pivotal role in photosynthesis, energy transfer, and the synthesis of nucleic acids, which are crucial for plant growth and development. By adding a complete fertilizer that is high in phosphorus, you can directly address the deficiency, helping to restore the health of the plants and promoting the development of healthy foliage. In addition, while it is essential to consider other factors such as soil pH, moisture availability, and presence of other nutrient deficiencies when diagnosing plant health, directly supplying phosphorus is a targeted and effective measure. Therefore, applying a high-phosphorus fertilizer can promptly alleviate the symptoms associated with this specific deficiency, leading to improved plant vigor and a reduction in purplish discoloration of the leaves.