What is a notable characteristic of rockwool as a soilless medium?

• A. Very low inertness
• B. High porosity and inert; may require pH adjustments
• C. Excellent natural nutrients
• D. High water retention and acidic

Answer: (B)

Rockwool’s standout feature in a soilless system is its high porosity paired with inert chemistry. The dense network of fibers creates lots of air spaces, giving roots excellent oxygen access and good drainage, while still holding adequate water through capillary action. Because rockwool is inert, it doesn’t supply nutrients or provide significant buffering, so all nutrients must come from the irrigation solution. That makes pH management essential to keep nutrients available to the plants; growers typically aim for a nutrient solution pH in the 5.5–6.5 range to optimize uptake. In short, the medium gives a highly aerated, well-draining root zone but relies on proper fertilization and pH control to meet plant needs. It isn’t a source of nutrients, and it’s not inherently acidic, which is why those other descriptions don’t fit.