May be they're more productive precisely because they're not raised :) YMMV of course but back when we tried to grow veggies, I noticed that raised beds perform dismally in FL. Sunken beds, on the other hand, were doing great and required much less maintenance. So pretty much anything all I do nowadays are inverted hugel-beds – sunken beds with some wood dug in. Additional bonus with those is that you can just add compost/mulch on the top and it'll find a way down itself.

Then again, I'm pretty brilliant when it comes to theories explaining why I shouldn't do things that smell or look like work :))

> I just find the raised beds easy to work around and nicely controllable.

They sure are. I'd love some table height beds :) But how fast will they go dry? Probably – very.

> I planted in some trench-style beds last year and had poor yields but I believe that was because I didn't loosen the soil.

Or may be water is not your limiting factor or may be you have too much of it even? We're on a sandy slope (up to 20%) here, so sunken beds did great (but to think about it – the terraces weren't too far behind) … They may be less of an advantage on flat wetter soil, I guess.

H-beds – From what I read about how they work in other places – they work about the same in FL, it's just that decomposition happens much faster here, so any wood less than 2" or so probably won't last over a year. On the other hand, I have a H-bed (raised) that I built about 5 years ago with 1'-2' diameter logs and it hasn't visibly collapsed yet … May be I need to open it and see what's going on there.

That reminds me of another experiment I did last summer – I dug a hole with a posthole digger and stuffed it with rolled up phone books and catalogues. Then I covered it with a bit of sand and planted cow-peas on the top of that hole and a few control holes (with nothing but sand inside). No irrigation except for the rain. Plants on top of yellow pages were about 3 times as big and lived a whole month longer into the Fall and almost made it to seed (I planted them pretty late, July, I think). I take it means that here water is the main limiting factor (and it's great to finally have a way to use them stupid catalogues for something good :)

Yes, I'm about to start doing some serious double-digging. The trial beds I did this past year worked really well, and needed a lot less tending than anywhere else I planted.

I had some success with raised beds, but that's only because they were less than 6" tall and placed in the lowest-lying area of the yard, receiving lots of rain run-off, and I have a permanent sprinkler there.

I've decided I'm going to identify all low-lying areas and double-dig beds there. Time to get things in gear for 2013.