"Perennialize" a typically annual vegetable

As I understand it, tomatoes and other veggies can be perennial in warmer climates than my own (zone 7). I've been thinking about how to make these type of plants perennial. There's a good chance I'm beating a dead horse here, but I just can't help myself, I love to experiment. The main difference between many perennial veggies vs annuals is that the perennials focus much of its energy below ground, and annuals like tomatoes focus most of its energy into fruiting. Please correct me if I'm wrong. The hardest part of planting perennial veggies like asparagus is waiting a couple years before harvesting it, but the plants need that time to establish its underground system. So, I've heard that for some plants, pruning them has a benefit of the plant putting more energy into the root system. Is it possible to plant a tomato and not allow it to fruit, but instead for the first year force it to put it's energy into its roots, and then before the first frost, mulch it heavily? Does all of that make sense? Thanks!

I don't know about frost-tender plants in temperate climates, but you can do this with some of the hardier veggies in many places simply by keeping the flowers/seedheads clipped off as they form. I can keep kale, chard, and broccoli going for several years this way. Eventually the plants become bushy and branched and the leaves/heads become so small that it's more work to pick them than it's worth and I start new ones.....or new ones start themselves, but that's self-seeding and another topic.
When I lived for a few years in Bangladesh, people would grow eggplant as a perennial. Eventually the plants would be up over your head and hard to work in and decline in yield, and they would be cut back severely and topdressed and make a whole second growth.....

tomatoes are technically perennial, but only in tropical climates, like central america, which i believe is where they are native. i think the best types for some kind of experimentation would be cherry size or currant type tomatoes, which are also the original wild or semi wild types. it's odd, or maybe not, but for some reason this is the third time i have heard this brought up in the last month.

when i lived in zone 9, i could over winter tomatoes, i had access to a sort of greenhouse ish area, and i would keep them in pots. unfortunately there i could nt get enough light and heat to make them happy though, so my experiments didnt work that great (weird microclimate). i could though get most of them to survive and to produce a bit through the winter and the next year, but it was a very small amount of tomatoes. it was nice, to get those few tomatoes in january and feb....

i think in a warmer, sunnier zone 9 or above, one could get tomatoes to be perennial, and to produce enormous quantities the following year. i have seen pictures anyway, of some mega tomato plants, being grown almost like grapes, with a roof arbor sort of dealio and tomatoes hanging down everywhere. so it is possible, just need to have a very warm climate.

actually i believe, now that i remember the last time i was talking about this with someone, that they pointed out it must be an indeterminate type of tomato.

it would be interesting experiment anyway, to do as you say, maybe keep cutting back the top growth the first year to force the plant to focus on root development, so that the second year you would have tomatoes.... but i am not sure this would be any better than just growing a tomato regularly, going to whatever lengths to overwinter it, then seeing what you get the second year.

what you are saying is true for many perennials though, the first few years its all about good root development, i just dont think it would effect tomatoes the same way.
for me tomatoes get killed as much by the extra moisture and lack of light, funks and moisture get them, and then the cold comes along and finishes them off. but i live in a warmer climate than you, my tomatoes are still producing bazillions of tomatoes, we just now reached the real fall time, and mostly because of the rain, they just started looking sad.

The main problem with trying to overwinter tropical vegetables (tomato, pepper, eggplant, lima bean) is that even if the root is protected by mulch from the frost, it can't tolerate several months of below 50 degree F temperatures and turns to mush. Its the same reason you don't store banana fruit in the refrigerator. If it is exposed for an extended time to temperatures below the range it is adapted for, its metabolism gets out of kilter eventually killing the plant.

And even if you are able to overwinter them, some plants like tomatoes have picked up enough plant viruses during their first summer that they are unthrifty when trying to grow during their second summer.

I love this discussion as it brings up so many more questions I have yet to find answers to. I was recently in Ireland and a friend showed me his rosemary bush which is a perennial there and I wished I didn't live In Minnesota so I would never have to work to grow rosemary again. I guess the best way to deal with this would be to eliminate rosemary from my diet but as a "civilized human" that seems preposterous!