Which soilless medium retains water well and is relatively pH-stable?

• A. Rockwool
• B. Coconut coir
• C. Expanded clay
• D. Perlite

Answer: (B)

In a soilless medium, the two key properties for healthy plant growth are how well the medium holds water and how stable the pH remains in the root zone. Coconut coir excels here because its fibrous structure traps a lot of water, giving the roots a steady moisture supply between watering, while its organic nature provides some buffering against rapid pH changes. This means nutrients stay available without frequent, heavy pH adjustments, which helps root function and growth.

The other media don’t combine these traits as effectively. Rockwool can hold water, but it can influence pH and often requires careful leaching to prevent buildup. Expanded clay drains quickly and doesn’t keep moisture around the roots for long, and perlite drains very fast with minimal water retention. So, coconut coir is the best fit when both high water retention and relative pH stability are desired.