In a flood and drain style Aquaponic system where a grow bed is flooded and then drained to mimic the natural cycles in an estuary, the plants need to root in a sub-strate, also known as media.
There are many choices for media including: pea gravel, washed river rock, expanded clay balls (commercially known as Hydroton) and expanded shale.
In Western PA, crushed gravel and river rock are problematic because of the limestone content which can wreck your fish tank’s water chemistry by the chemicals that naturally leach from the rocks. The media needs to be pH-neutral
Hydroton and expanded shale can be very expensive: $30 for a 50 liter bag is common. We need a grow media that is more affordable.
A local Aquapon from Sewickley, Tim Kelly, discovered that crushed black granite works well as a grow media. It does not affect the water chemistry and it is affordable.
While many beginning Aquaponic gardeners can spend $100 alone on grow media, Tim spent that amount on his entire Aquaponic system!
Inspired by agri-preneurs like Will Allen (Growing Power in Milwaukee) and John Edel (The Plant in Chicago), Tim built himself an aquaponic system that proves out the technology using crushed black granite as a grow medium. See the photo below:
So far, Tim has only had success growing cherry tomatoes, but he admits that conditions were not ideal (partial shade) and that his system is very small. To buy the crushed granite, visit Fratangelo Gardens in Coraopolis, PA.