Certified Professional Horticulturist (CPH) Practice Exam

What is the stage where a plant cannot recover from loss of water?

1. Turgid Point

2. Permanent Wilting Point

3. Point of Field Capacity

4. PAW

The correct answer is: Permanent Wilting Point

The stage where a plant cannot recover from loss of water is known as the Permanent Wilting Point. At this stage, the soil moisture is so low that the plant's roots are unable to extract sufficient water to maintain cellular turgor pressure. This leads to irreversible wilting of the plant cells, causing the plant to become nonviable and unable to revive even if water becomes available later. Understanding the Permanent Wilting Point is crucial for horticulturists because it marks the threshold that indicates a potential critical condition for plants under drought stress. Sustainable watering practices aim to prevent plants from reaching this point. Other options represent different levels of soil moisture and plant health. The Turgid Point refers to the optimal condition where plants are fully hydrated. The Point of Field Capacity reflects the maximum water content of the soil after excess water has drained away and the soil is at saturation point, but still able to maintain some moisture for plants. Plant Available Water (PAW) encompasses the water that is accessible to the plants within the range of field capacity to the Permanent Wilting Point, indicating that plant health can be sustained within this range.