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curious newbie

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Hello! I'm a bit curious about the types of media (rock wool from Grodan, coco coir, etc) available to grow Marijuana, so I have a few questions!

What type of growing media do you use and why?

For Grodan's products or other types of rock/mineral wool, what issues have you come across?

How do you dispose the growing media when you’re done?

If you use mineral wool, what percentage of your cost goes into buying mineral wool

Hoping to hear from someone!

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Good question, I use soil to grow my plants indoors or outdoors and I use mineral and organic nutrients, but I always flush the plants 2 weeks before I harvest them and then just give them water so they use up whatever nutrients are available, so the end product smells as tastes as it should.

If your just starting out and working out how your going to forward I would advise using soil that is for growing Cannabis simply because it is so forgiving if you mess up your less likely to kill your plants, if your start with coco you really need to own it, you will be responsible for providing everything the plant requires to thrive.

Disposing of the spent dirt I have not found any problems I take it to the local council tip where you can dump all sorts of garden waste.

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@curious newbie, You are right to be concerned about the cost of medium.  Grodan products are good, but they are proud of their products, and that is reflected in their price. 


You can create your own rockwool growing cubes!  Somewhere in my past journals, I have shown in detail how to do that.  Making your own rockwool cubes is MUCH cheaper than purchasing ready-made.


I used rockwool purchased from a home improvement store (block rockwool, not loose rockwool.  Block rockwool is normally used to insulate and/or to provide fire-breaks on the outside of buildings before being layered with stucco or some other fascade.)  Block rockwool usually comes in a size comparable to a square bail of hay, and it is usually encased in a plastic wrap.  Opening the plastic wrap, you will usually find the cube is pre-cut into either two or four pieces length-wise of the bail.


I used a knife (specifically made for cutting rockwool) to cut my blocks (both the seedling cubes and the growth cubes).  Approximating the size of Grodan cubes.


I used a hole-cutter (inch and a quarter, or 25 mm) to cut out my plugs, and to make plug-holes in the growth cubes.  (Normally, a hole-cutter is driven by a drill, but for this work, you can most-easily cut the plugs and holes just by spinning and pushing the hole-cutter bit using your hands.)  You have to estimate the depth you want, and then using a screwdriver or your long fingernails, grab or dig-out the plug.


For the outer plastic wrap, I used a good quality duct tape, making sure to seal it by overlapping at least an inch or so, so that it will hold even after it gets wet. 


Cutting 1/4" grooves in the bottom of the growth cubes (similar to the Grodan cubes) will help drainage and oxygen getting to the roots.


Issues:  Rockwool must be soaked for a day or two or three before use.  Rockwool always drives the pH up, up up.  You MUST drive the pH in that soaking water down, down, down until it finally stabilizes at about 5,8 for the long soak.  Check and adjust it each day.  You will need to contrive some method to push the cubes down into the soaking water (without crushing them) to ensure they are 100% under water; they want to float like crazy.


If you are careful with your rockwool cubes, you can re-use them once, maybe two times.  Allow the cubes and roots to dry-out completely, and then the old roots are easier to remove.  During the normal use of the grow cube, the duct tape is removed before the intense vegetative stage (usually about the same time that the adhesive fails due to the moisture), so obviously, a re-used cube will need to be re-wrapped with duct tape before the next use.


When the rockwool is no longer usable, you may dispose of it in regular construction rubble or regular house trash (depending on your local waste disposal laws),

or you can rip it into chunks , re-soak it to clean it and use it as a growth medium called "mapeto" (that method is also somewhere in this forum, or google "mapeto growing method" to learn more),

or you can grind it down to dust and throw it into compost bins; it is just a mineral rock and will mix well into a garden soil, helping to provide drainage.  (Wash it off your skin afterwards, otherwise it may become itchy.  But most importantly, be careful not to breathe it in.  Either work in a breeze or wear a dust mask, or both.  In the lungs, it could contribute to Silicosis.)


Hope this helps...

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