Grodan Growcubes 5.3 Cubic Fee. It is almost impossible to over-water your plant when using Gordan Growcubes. These small loose cubes of stonewool provide your plant with better aeration and maximum drainage. It is also easy to mix this stonewool with other loose media (such as expanded clay rocks or coconut fiber). It is also lightweight and much cleaner than peat-based media! The properties of Growcubes make it like a 50/50 mix of absorbent to repellent stonewool. Loose Box.