Picture posting is enabled for all :)
Never heard of a food trench before. Do you have any links, terrace?
Do you leave the trench open all winter or cover it over every time you put new waste in? (sorry if that's a bit dim, my excuse is its late and I'm tired ::))
Nope I don't do any of that. They seem to grow well enough without any special ground preperation. I spread some compost at the begining of the year and build a support frame.