Greenhouse tomato's

I was just thinking ahead about greenhouse tom's, i have seen some place that you can grow them in a bottomless pot that stands on the GH border, i would like to give this a go next year but can not remember the details, any help on how and why?
Reg

It's called ring culture if I remember correctly.  Typically you fill the trench with gravel rather than compost, and compost only in the bottomless plantpots.  Rationale is that tomato shallow roots take in feed and deep roots only water.

We grow in a trench of compost in a "modified" ring culture method in the lottie greenhouse - works great - massively productive plants every year since we started using the method.  As already said, majority of water in the trench, water + feed into the pots.