Certified Professional Horticulturist (CPH) Practice Exam

Which indoor plant condition is most commonly associated with low humidity?

1. Root rot

2. Leaf drop

3. Powdery mildew

4. Fungal infection

The correct answer is: Leaf drop

Leaf drop is a common symptom associated with low humidity in indoor plants. Many houseplants, particularly tropical species, thrive in environments with higher humidity levels. When the humidity drops, these plants can become stressed, causing them to lose leaves as a survival mechanism. This response to low humidity occurs because essential processes like transpiration and nutrient uptake are affected. Plants lose moisture through their leaves, and in a low-humidity environment, they cannot maintain adequate moisture levels, leading to leaf drop. Additionally, the loss of moisture can disrupt the plant's ability to provide essential nutrients to its leaves, further exacerbating the issue. In contrast, root rot primarily results from overwatering or poor drainage, rather than humidity levels. Powdery mildew is more typically associated with high humidity and poor air circulation, which encourages fungal growth on plant surfaces. Fungal infections can also arise from excessive moisture, but they are not directly linked to low humidity. Thus, the relationship between low humidity and leaf drop is significant in understanding indoor plant care.