Dahlia tubers

Certainly you can keep the tubers, they can be left in the ground if your soil is well drained so that they dont rot, but to be on the safe side its perhaps best to lift them. Dig them up, allow them to dry & remove the soil residue then store them in a dry, dark place (a box maybe in the shed) some people store them in their house. Then start them off again in spring. Trim any thin weak roots off leaving plump healthy tubers. Start them off in a tray of shallow compost, up to (but not covering the crown), keep them moist & before long they will start producing shoots which you can take as cuttings to pot on & wait for more shoots before planting the whole tubers.
This year I took 8 cuttings from 3 B.of Llandaff tubers which are now garden ready & the tubers are now planted in the garden & doing great so give it a go.

Hello Poppy - thanks for answer. Do I cut the shoot off the tuber and plant it or cut the piece of tuber off the remaining tuber with the shoot attached to it? Does that make sense?
Sheila

Take a cutting from the shoots off the tuber when they are 2 or 3 inches, so strong enough to be potted up in sowing compost in a small pot. Don't cut into the tuber itself. The tuber will keep sending out more shoots. Good luck. I will put a pic of my cuttings taken about 3 months ago.