What to do with Used Rockwool?

[Adam Dusen]

I looked to see if a topic existed on this already, but could not find one through the search function. I am interested to know what uses people have come up with for their used rockwool. Any rockwool that is in decent enough shape I will usually dry out again, remove the dried roots, and reuse until it is no longer good enough to use anymore. But at that point, I am not sure what to do with the stuff other than just throw it away. Someone who managed this system before me was just adding it into our compost (despite the fact that it clearly is not compostable), but I can say from experience that it just clogs up the garden beds... I still am pulling that stuff out of the gardens months later.

I have heard from somewhere that some people will use a shredder to finely shred it and then mix into compost or potting soil and I could see that being more practical but do not have a shredder yet to give it a try. Has anyone tried that? Any other uses out there others have tried (successfully or unsuccessfully)?

[Derek]

Rockwool is made by melting a combination of rock and sand
and then spinning the mixture to make fibers which are
formed into different shapes and sizes. The process is very
similar to making cotton candy. While versatility and ease have contributed to its
popularity, there are several disadvantages to this type of
growing medium which should be considered along with the
pros before deciding on whether or not you want to use it.
Advantages of Rockwool
RETAINS WATER - Rockwool holds an incredible amount of
water which gives you a buffer against power outages and
pump or timer failure.
HOLDS AIR - Rockwool holds at least 18 % air at all times
(unless it is sitting directly in water). This supplies the root
zone with plenty of oxygen, making overwatering less likely.
COMES IN A VARIETY OF SIZES AND SHAPES - From 1"
cubes designed for use in propagation, to 3"x12"x36" slabs
capable of holding the root systems of huge plants, Rockwool
comes in many sizes, including loose so you can fill pots or
containers of any size.
CLEAN AND CONVENIENT - Rockwool holds together very
well so it can't spill. It also comes wrapped in plastic, making
it easy to handle and keeping evaporation to a minimum.
Disadvantages to Rockwool
NOT ENVIRONMENTALLY FRIENDLY - Rockwool is hard to
dispose of. If it is buried, it will last indefinitely.
DUST AND FIBERS ARE A HEALTH RISK - The fibers and dust
from the Rockwool are bad for your lungs. It is strongly
advised that you wear a dust mask when handling it to prevent
problems.
pH PROBLEMS - Rockwool has a high pH which means you
have to adjust your nutrient solution low so that the root zone
is neutral. Rockwool is also susceptible to pH shifts meaning
more routine maintenance to keep the pH levels correct. So no I don't think there are any uses for it after its been used. After all its glass. So the best thing to do is recycle it with other glass. Just don't put it in your planting beds because it won't decompose. You can try coconut fiber.

The main advantages of coconut fiber are its oxygen and
water-holding abilities. It can maintain a larger oxygen
capacity than rockwool yet also has superior water-holding
ability. Some research has also shown that coir might have
insect-repelling abilities. It also has the advantage of not containing any, or extremely
low, levels of nutrients, so it won't alter the composition of the
nutrient solution.

Hope this helped.