Some plants grow better in my raft, others in my flood and drain?

[Stacey King]

I'm running a humonia system. I have a system of 6 half barrels, at the first end are two raft barrels, the other four barrels are flood and drain. The pump runs to flood the beds 20 times per day, 32 minutes pump and 40 minutes drain.

Now after some time to get to know it, I have determined the following:
Beetroot lacks phosphorus in the flood and drain and will not grow at all. It grows well in the raft. (of course this is not especially useful for a root crop so I grow it in soil instead)

Lettuce grows slightly better in the flood and drain than in the raft.

Peas grow just fine in the flood and drain. Have not grown it in rafts so far, so no comparison.

Carrots grow equally well in both flood and drain and raft areas. Better than in soil.

Silverbeet does not grow in the flood and drain. Have not tried it in rafts yet.

Celery grows very well in the flood and drain. Better than in soil. Lovely roots too. Have not tried it in rafts yet, but will this week.

Peppers grow well in the raft, but not at all in the flood and drain, although their roots do very well indeed.

Root health in the flood and drain is excellent. If anything, slightly better than in the raft area.

Now why the difference? I thought initially that my flood and drain was not good for growing, but that has been disproved. Several crops grow just fine in it.

Some I have compared and they grow equally well in either area. One oddity (lettuce) actually grows better. Fractionally better, but still better. Why?? I'm confused ...

[Jim Fisk]

Personally I am planning on turning our 3' x 13' x 10" dwc into media (granite) flood and drain any day now. I find no advantage to raft in a home food factory system other than it has next to no effect on the 275g buried sump (no ebb and flow). I am sure the sump will handle it however. In a production facility where you pick the entire plant for market I can see the value but we often keep plants growing for months and even years by just harvesting partially for meals. Tired of running aerators and ozonators to avoid root rot. Everything we have tried has done fine in the media. Flood and drain rules for us and our bell siphons have been online for 3+ years without interruption.

[Stacey King]

Sort of the opposite to what we've got. Mostly the DWC does better, although there is a lot of attention needed to its bubblers to clean the holes out.

We were considering converting the next two of the flood and drain to rafts, leaving us with just 2 flood and drain beds for the comparatively few plants that do better there. But I'm afraid it may be too little area in media.

So right now I'm just trying different things, so that if I can't help even out the differences, then at least I can just adapt to plant the things that do best in the different places. But I'd really like to fix it!

Some people said that the flood and drain area was probably lacking oxygen and needed to drain quicker ... but we waited to see, because converting our timer system to a quicker drain would be a major re-haul, and now it is pretty clear that isn't the problem. Root health is excellent, and some plants do so well.