The leaves look like certain mint leaves and the little cluster of colorful flowers.

Is it a perrenial? I cannot tell there is any bulbs just a hairy root system. Or will they die in the winter?
I planted them kind of close because I would like to see multiple colors. But I see in public there are some single color big clumps of verbena about 2-3' across is that how big they will become? Am I supposed to prune them back to control the size?

Thanks in advance for your opinions.