Rock Wool Medium
 

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.

https://firstrays.com/wp-content/upl...0/08/cubes.png

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.

Thank you very much for this info Ray.
I just had a look, I can get those Grodan cubes here in Germany too.
If this works I would repot all my phals before the winter :biggrin:
Please keep us up to date.

this is a really interesting experiment....i have seen rock wool in hydroponics for years and i recently got two plants from Marlow that were mounted with a bit of rockwool under the plant over the cork.

i know that the "downside" of the rockwool is that it will degrade and eventually become a place where there will be no air movement - i feel like this takes YEARS like when you unwrap a store bought phal and there are three layers of sphag from the three up-pots and then a small clump of sandy rotten rockwool in the middle where those roots are often in poor health.

please keep this updated

It is an inorganic glass. How will it degrade?

I have played with the stuff previously, when it was only available as loose batting in either hydrophilic or hydrophobic form. I do know it will compress over time, but these cubes have better structural integrity, and I am planning on using them as a secondary additive to LECA, not alone, so I don't know how much compacting will take place.

With that retention of water over time, it seems like the cubes would be a natural for catasetums.

maybe it just compresses to the point of sandy and it is the other stuff..plant material and sphag that i am seeing as rotted.


in the description you describe it sounds perfect...

..i am going to get a box and try it in the catasteum mounts i am making, as fishmom pointed out


i think i am about ready for klite

Is it safe?
I had some nasty experiences with rock wool in my professional life.
There are several types of this material...

Grodan is the industry leader for rockwool substrates, so yes, horticultural grade rock wool is safe, though standard prcautions should be taken when manipulating it (gloves, avoid working in closed spaces due to small particles). We order the stuff by the truckload for our plants at work.

Camille, is this similar to wetting perlite before using it, instead of inhaling big puffs of dust when you use in the garden?

Perlite can mess you up. Those particles are deadly