Certified Professional Horticulturist (CPH) Practice Exam

What is the role of perlite in potting mixes?

1. To retain water

2. To improve aeration

3. To add nutrients

4. To stabilize pH balance

The correct answer is: To improve aeration

Perlite plays a crucial role in potting mixes primarily by improving aeration. This volcanic glass, when heated, expands and creates a lightweight, porous material that increases the air-filled porosity of soil. Good aeration is essential for healthy root development as it allows for proper oxygen exchange in the root zone. Roots require oxygen to respire; without adequate aeration, plants may suffer from root rot and other health issues. While perlite does not retain water as effectively as some other components like peat or coconut coir, its structure helps create space in the mix that can hold air. This property allows for a balance between water retention and drainage; thus, improving the overall moisture management in the potting mix. Therefore, the correct identification of perlite's function highlights its essential role in promoting healthy plant growth through enhanced aeration.