| I'm not sure whether you are asking which plants require a TRELLIS v. simply requiring some support to grow up against. I very deliberately avoid using any kind of trellis whenever possible--untangling dead vines from a permanent trellis each fall is murder. Instead I use cotton string and train vines to grow up that. At the end of the season, I simply cut the strings and throw the entire mass into the compost--strings and all. It's an easy five minute job rather than a couple hours having my hands rasped by plant bristles. The plants that I train up the strings: Pole peas, pole beans, cucumbers, bitter melon, vining varieties of squash, vining melons. You should not need support for the eggplant--I've never met a vining eggplant. Determinate tomatoes should be non-vining, though I've had to stake a few in the past to keep them from flopping over. A few of my pepper plants as well needed staking. I suppose the eggplant could flop if the stem isn't sturdy enough, but it should not require trellising. | 
