Rock Wool Medium

[camille1585]

Originally Posted by WaterWitchin

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

Horticultural rockwool has a much more compact structure than the stuff used for insolation, so the amount of dust is far, far less. At work we use blocks or slabs which are partially or entirely wrapped in plastic, so there is only a small risk of skin irritation or inhalation. With the small cubes, you get a bit more dust but it's still nothing compared to insulation rockwool.

All rockwool products need to be soaked before use. One reason is to have a uniformly wet substrate for good initial root development. The second and most important reason is to lower the pH. During the manufacturing process residual lime is left in the rockwool, which increases the pH. The starting pH of rockwool is around 8, so unless it is sufficiently soaked beforehand, pH will stay high or even continue to increase during the early stages of cultivation. A good soak and flush of the cubes will remove a lot of lime, and if you water in sufficient amounts once the plants are potted, it will continue to flush it out.

Another option is to soak the rockwool in water at pH 5,5-6 to dissolve the lime and bring the cubes done to the proper pH immediately, taking care to avoid having the pH dip below 5, at which point the rockwool itself will start to degrade/dissolve (leading to a compacted mess similar to what DC describes). At work we soak out rockwool in the nutrient solution used during cultivation, with a pH of 5,8.

In french orchid forums it's often instructed to repeatedly soak the cubes over the course of several days until the pH no longer increases, but unless you are using a recirculating nutrient solution, this is not necessary. With standard watering practices (the excess water is thrown out) at each watering a little bit more lime will leach and drain out.

[DirtyCoconuts]

What a wealth of knowledge!! Thank you for taking the time to share all that!

[Ray]

That's interesting, Camille.

I took the cubes right out of the box, filled the plastic food container with RO water and capped it. About 36 hours later, the pH was 5.4

"Splain that one"

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By the way, "dust" is really not an issue with the stuff I have. Having tiny pieces of glass fiber poke your fingers is possible, but seems to only be an issue when dry.

Sure, it is possible that there could be airborne fibers, but that appears to be a very small likelihood unless you start tossing the stuff in the air.

[camille1585]

You got me there Ray! And I can't find information on why that's the case. I did find a passing mention that major manufacturers are now pre conditioning their rockwool before it leaves the factory.

[Tim P.]

I grow my phrags exclusively in rock wool. It is the same brand that you are experimenting with, and they love it.

Word of caution. Moisten it before use. Glass fibers in the lungs last forever.

One other issue I have with it, is that it loves to grow moss in my clear pots. Other than that, I really like it. I have yet to use it on anything other than phrags. What plants were you going to use it on?

[SouthPark]

My two phrags are growing in rock --- not rock wool. Scoria that is, and doing great. The rock wool definitely sounds workable - but the fibres in fingers and/or lungs - even 'low risk' is still a risk of some sort. But if safety precautions are followed, and one knows what they're doing - then maybe ok. As they say - it's not the low probability that people are scared of. It's the event of an unwanted occurrence actually happen and come true - is what some people should be scared of. Such as a slip-up or something.

Although - for a very experienced grower such as Ray ----- he would likely be careful, and everything should be ok. It's other growers that don't understand the risks - is a bit of a concern.

[Ray]

Originally Posted by Tim P.

I grow my phrags exclusively in rock wool. It is the same brand that you are experimenting with, and they love it.

Word of caution. Moisten it before use. Glass fibers in the lungs last forever.

One other issue I have with it, is that it loves to grow moss in my clear pots. Other than that, I really like it. I have yet to use it on anything other than phrags. What plants were you going to use it on?

My paphs and phrags do very well for me in semi-hydroponic culture using LECA, so I won’t be messing with that. I grow my phals in sphagnum, so they seem to be likely candidates, but I have a couple of bollea/warczewiczella/pescatorea intergenerics (also currently in moss) that might be the first choice.

I’m not too concerned about the handling. I’m a ceramic engineer who has worked with all sorts of glass, powder & chemical manufacturing, including radioactive powders since grad school, so I’m pretty well trained in safe handling.

[WaterWitchin]

I got some to mix in toward top of LECA in some of my SH pots. Experimenting with lowering evaporation rate.

[camille1585]

Originally Posted by WaterWitchin

I got some to mix in toward top of LECA in some of my SH pots. Experimenting with lowering evaporation rate.

How is that working out so far?

[WaterWitchin]

Originally Posted by camille1585

How is that working out so far?

Haven't done it yet. But I'll sure let ya know!