Answer: First of all, make sure if your house is being sold that the contract allows the plants to be removed. (Usually, it does not.) Next, consider whether or not your ultimate location will provide the right growing conditions for the plants you have now, and whether or not they could be replaced easily with the same or similar cultivars. (Keep in mind that perennials age, require division and ongoing care, and most do not live more than a few years.) The reason I mention these kinds of considerations is that, unfortunately, this is really difficult to do.
The best thing would be to use a friend's garden to temporarily hold the plants for you. Or, perhaps you could quickly create a temporary garden spot at the new location and plant them there until you can devise more permanent beds. You can dig them, pop the rootball in a plastic grocery bag to prevent drying out, keep them cool and shaded for a day or two and replant. This usually works fairly well.
You might be able to pot them up and maintain them as container plants however it is very hard to keep them healthy for such a long time under home conditions and in my experience it would be better to have potted them up in late winter or early spring. Most mature perennials would need large containers, possibly two gallon size. You would need to use a soilless potting mix and clean the roots somewhat prior to potting them up -- garden soil does not work well in containers as it tends to harbor pests and also compacts too much over time so it won't hold air and drain well.
You will also have to figure out a way to protect the roots during the winter. The extreme cold combined with the spring freeze thaw cycles are very stressful on plants. You might be able to store them in a coldframe, an unheated garage, or possibly in a very sheltered location with mulch heaped over and around the pots (but not over the crowns of the plants).
I am sorry I can't be more encouraging, and I know how heartbreaking it can be to leave a perennial garden behind, but it's just that this is a very difficult thing logistically to try to do. Good luck with your move!
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