When I try to grow "upside-down" tomatoes, they always curve back up towards the sun and eventually break, causing massive damage. Could I be doing something wrong, or is there a way to avoid this?
There was just an article on upside-down planting in the June 2011 edition of Consumer Reports on this topic. They tested out topsy-turvy tomato planters to see how tomatos grown in these containers compare to traditionally planted tomatoes. Their answer to your question:
Tomato shoots are geotropic: They try to turn up in response to gravity. But Topsy Turvy plants slump as they grow, often twisting their stems, which can cause splitting.
It may be interesting to experiment with growing indeterminate vs. determinate tomato plants in your upside-down planter. Determinate plants are bushy and more rigid, indeterminate are viney. I would think the flexible/bendable nature of indeterminate tomatoes may make them less likely to break in an up-side-down planter.