Step 6: Scaling up for bigger, fancier systems

Picture of Scaling up for bigger, fancier systems
These systems can scale up to commercial size, like this greenhouse at the Center for Sustainable Aquaponics.
You say to hang burlap strips for roots to adhere to, but how do you get the plants to stay in there? Is there rock in the vertical tubes? How are they started and what are they put in to stay in place until the roots take hold?
You would put the lettuce plugs or whatever kind of plant into the holes you've drilled in the PVC. Here's a link to the kind of plugs you could use for example: http://www.harrisseeds.com/storefront/t-PG_Plugs.aspx

The root-end of the plug would be touching the burlap strip and the roots would grow into it.