Flood & Drain vs. DWC?

[Bob Vento]

Have been reading posts from various folks here and a question comes to mind ...
Flood & Drain vs DWC?

Some folks are saying that greens grow better in the DWC system, but what about the filtration for the FT? Seems that without the media the water would have no filtration. Could someone please help clearify the advantages and disadvantages?.

[TCLynx]

Greens grow just fine in media beds.  Rafts just make the labor of planting and harvesting large amounts of the same crop easier and thus work well for growing large amounts of greens in a commercial setting.

So, how does a raft system handle filtration?

Well in a very low density setting, the surface areas of the bottom of the raft and the insides of the raft bed and even the plant roots as well as the walls of the fish tank can provide enough surface area for bio-filtration and since in one of those micro systems there isn't any solids filtration the fish poop will need to be siphoned out occasionally or whenever the plants start showing signs of problems from solids building up on roots.

More commonly, large scale DWC systems will use settling tanks and net tanks and degassing tanks or other types of separate bio-filters and solids filters to deal with filtration separate from the plant growing space.

The advantages of DWC seem mostly to be with avoiding the use of heavy media and streamlining the labor of planting/harvesting for commercial operations.

The advantages of media based systems (either flood and drain or constant flood) are that the plant growing space and filtration are included in the same component and you can have worms live in the media bed to help further convert the solids into plant food.  Media based systems also have the advantage that the garden beds are more like traditional gardening in that you can simply plant seeds or transplants into the beds and you don't have to worry as much about supporting heavy plants in a foam raft.

[Bill Moore]

TCLynx...   looking for conversation on hole spacing in the raft (foam board).   Also any recommendations on which type of foam/insulation board to use from sustainability and off-gassing perspective?

[Vlad Jovanovic]

From a sustainability standpoint...start growing lots and lots of Reeds and maybe some bamboo...but you will in all likelyhood find extruded polystyrene preferable. This is sold in the big box stores as Dow Blue Board. It (unlike the expanded polystyrene) is a homogenous texture (not made up of tiny little balls crunched together like styrofoam) and with an average of 30kg/m3 is a good deal stronger.

Dont get the 'score' board, or the tongue and groove board (like I had to here, cuz they dont sell the square edged board anywhere in the region).

A guy in the Raft/Deepwater Culture growers group has an interesting take on what to me appears to be a backyard/modified Kratky growing method. But it seems like a lot more work than the Dow polystyrene. Might not be bad if you don't have too many rafts to make. http://aquaponicscommunity.com/group/raftdeepwaterculturegrowers

Spacing is going to depend on what you are hoping to grow out, and to what size...And there's some talk over there on the topic if I remember correctly.

[TCLynx]

Looks like Vlad covered pretty much what I might have said.  I'm not a raft grower really so anything I would say on the subject is hearsay.  Oh, most people paint the tops of the boards to help them last longer under the sun.  Make your spacing big enough for the plants you intend to grow and your latitude to make sure everything gets enough light.

[Bill Moore]

Here's my first rough calculation:  Bibb lettuce at 6 inches apart or 16 head per 2x2ft raft.