Over at the Slippertalk forum, there are folks that use Grodan rock wool cubes for their phrags, so I thought I'd get some to experiment with.
Grodan is a long time manufacturer of inorganic rock wool horticultural media. This product is manufactured by melting basalt and spinning it into fibers, much as insulating fiberglass is made. The fibers are produced as a mat, then cut into smaller pieces for use. In this case, they approximately 1 cm cubes. The fiber is approximately 50/50 hydrophilic/hydrophobic, so is supposed to remain fairly airy.
I did a little experimenting before use:
- I filled a container (roughly equivalent to a 6″ pot 6″ tall) with the dry cubes – they weighed only 2.25g.
- They were soaked in RO water for 36 hours
- Saturated, they weighed 308g. After 5 days of sitting open in warm, humid air, only 15% of the water had evaporated.
- The saturated cubes occupied approximately 55% of the container volume, leaving 45% air space.
- The pH of the soak water was 5.4, so should be fine right out of the box.
- The EC was only 20 µS (for reference, a 100 ppm N solution of K-Lite has an EC of 710 µS).
I am planning to experiment with my phals in a mix of LECA and cubes (75/25? 50/50?). I currently grow them in straight sphagnum, because the evaporative cooling in S/H pots in my home in winter cools them too much.
I can conceive - based upon the water retention - that a blend will serve to "flatten" the moisture gradient in an S/H pot, keeping it moist to the top.
If anyone else wishes to play with it, I have a
few boxes available.
Rock Wool Medium
Threaded Mode
