The International Banana Society has a number of excellent threads on the subject of preparing bananas for overwintering both inground and out. Do you know which species or cultivar of banana you're growing? Hardiness varies greatly - for example if you have Musa basjoo, you'll be fine simply removing the leaves and mulching it in heavily. However, if you have an edible cultivar, say 'Dwarf Cavendish,' this will need to be dug up and brought indoors for its dormancy period.
Larger more established specimens of Musa basjoo never need winter protection (here). If you've had yours in ground for a couple of years and there's numerous stems, no worries, they'll just pop up each spring. Newer plantings it's suggested to have a mulch to protect the establishing root zone. Potted ones are much more at risk of winter damage because the roots can freeze much easier being above ground. As mentioned, Bananas.org is a wealth of info, and for the record (I always try and point this out), bananas are not trees and do not form a true trunk. They're herbacious perennials that produce a pseudostem rather than a trunk. Cheers, LPN.
