Growing Medium


Several types of growing medium are available for hydroponic systems.  Because we used the ebb and flow system, I will only be focusing on the products we used as those are the ones in which we have experienced first hand.

I will start with a product widely used but seriously scores a NEGATORY on the environmental niceness scale:

Rock Wool

Rock Wool

This stuff has all sorts of applications and used in industries for things such as car manufacturing, soundproofing and house and commercial building construction as well as for growing medium purposes.  In some cases, it is considered a necessary evil, but is still not ideal to use unless necessary.




Yes, shame on us, we know now that it’s not the greatest medium to use and does not bode will for the environment for sure.  This stuff has a burn rate at a staggering 1200 degrees!  Just for kicks, here is the MSDS: MSDS Grodan Material.

Now, that being said, we did use it and found that in some instances it does have some benefits. As we were getting our tables going, we used the rock wool as our starter medium and found that it has great benefit in holding moisture.  This was a plus because we didn’t have to flood our tables as often using the rock wool medium as we would have if we were using other mediums.  Cuts down on electrical costs.



Large Rock Wool

There are several sizes of the Rock Wool that can be purchased.  We used the smaller blocks for our starter medium, but also used the larger blocks for cultivars which are very dense and have a high water requirement such as cabbage.  They worked out beautifully!


Enough about Rock Wool.  Lets move on to the other type of medium which is much safer and can be reused.


Hydro Pebbles

With respect to the pebbles, we personally used the brand Hydrocorn, its much safer for the environment and in our case, we reuse our old pebbles in our outdoor vegetable garden when the indoor season is over.  Waste not, want not.


Thhydrocorn bage pebbles hold quite a bit of moisture; however, it does not hold quite as much as the rock wool.  When we were first starting our plants we were breaking up the pellets to increase their absorption and water retention for our little rootlings.  Depending on how big the indoor garden is, it can take quite a bit of pebbles so be prepared for the cost.  Hydrocorn is not the cheapest, but is considered the gold standard for the indoor grow industry.  There are benefits to the brand, but cost is not one of them.  I am sure that the cheaper pellets may be as good but since this was a new adventure for us, we decided to use this brand as a “experimental control” as it were.

Using a combination of the two worked out well for us this season; however, next season we may try other types of medium to get away from the rock wool.




‘Here is a good representation of our starter table and how we used each of the mediums.





I also used a combination of both  mediums when preparing my combination lettuce tray for the hydroponic table.  I drilled holes in the bottom of a plastic window box planter, used a mesh platform to leave some space in the bottom and used the Hydrocorn as my main growing medium and the rock wool as my starter blocks.  20170312_213353.jpg