I live in USDA zone 5 and have banana plants planted in the ground. I know I need to dig them up and bring them in (I left them out one year and covered them up but they didn't survive). The question is do I put them in pots in front of a sunny window or hide them away in the cool basement?
Where do you live? How long have you had these plants? How long have they been planted in your garden? To move them now if they are not root pruned and acclimated to the indoors will be risky. Depending on how much time you have before the first freeze, you need to use the time you have left to give your plants some transition support.
First you need to let the roots know they are going to have to make do with a lot less roots. To do this you need to make a trench around the base of your plants as they are in the garden. I've no idea how big these plants are and how long they've been in the ground. Let's assume they are 2-3' in height, cut a circle around each plant with a 6" radius. Use a flat shovel to make your cuts. You might want to dig down to see how big the root mass is to determine the radius. Focus on the mass not the single roots growing outward. Cut down 6" deep keeping your plant in the center of the circle. Next, cut another circle with a radius of 9 to 10", 6" deep. Scoop out the soil between the cuts and fill with straw. Water well. Be nice to have a few weeks (more the better) to allow these plants to get used to the severely reduced root mass and begin to grow new feeder roots.
Let's say that we figure 2 weeks for adjustment to the root pruning. More the better! Allowing another 2 weeks before the first freeze, dig out the plant and its root ball. Transplant into a pot that is 2-3" larger than the 6" radius or a 16 -18" pot with drain hole. This pot will be its forever home...well, until it needs transplanting into a larger pot in a year or two. Use good potting soil, not the garden soil. Water and allow to dry out before watering again. Find a southern exposure but no direct sunlight in your home for its place this winter.
After you have transplanted your banana trees, watered, allow to drain start their acclimation to the indoors. Bring them in for 2 hours then take them back out. The next day do 3 hours and take back outside. Each day allow another hour more until you reach 12 hours. Do for 3 more days. Then bring them in for good. This is the fastest transition but we can always try faster, with much more risk. Ideally, you would take at least 3 or 4 weeks for acclimation but I am just trying to figure out how to squeeze in the necessary adaptation in the shortest amount of time. No guarantees. Need more information and pictures for sure.
I am hoping you have at least a month before the first freeze. If not do you have a friend with a green house? That would be a good transition from root pruning and transplanting to a similar temperature environment and then have a bit more room to do the acclimating to the indoor environment. Where do you have these plants located right now? How long ago were they planted? This is but one solution depending on how close my assumptions have been. Pictures please!
Digging up plants that are used to living out of doors to take them inside without a transition will flat out kill them. Have you ever tried to buy a live tree in a pot for Christmas? If you want to have a live tree to plant in the garden you have to acclimate your tree to the indoors.
With the time you have remaining it will be a bit of work to get them to adjust to using less of a root system. Then we need to acclimate them to far less light, dry dry air, forced air vents at the same time dealing with the newly chopped roots. Stresses on top of stresses. Ideally, we would never have planted them in the garden in zone 5. They need to stay in pots that are able to be taken outside during the warm season and acclimated to coming back inside. Send more information about where you live and how much time before the first freeze. Do you have a friend with a heated greenhouse? Start the trench with straw to root prune your plants NOW. Get an almanac or talk with locals for a better feel of the weather.