Dahlia tubers should be left in the ground until frost. At that time, cut stalks to a few inches above the ground. Each dahlia will have turned into a clump, which needs to be lifted carefully with a garden fork or shovel. Be careful not to damage tubers when digging as this can cause rotting during storage.

The clump should now be rinsed with a hose gun attactment to free it from soil. Remove any attached rotted tubers with sharp pruning shears, then dip entire tuber clump in a bucket of bulb dip to help ward off rotting and insect problems during storage. Alternatively, tubers can also be dusted with fungicide when packing them away. Allow the clump to dry under cover in a protected area, such as a garage, for 24-48 hours. Tubers can now be marked with a sharpie.

Pack tubers in crates or other container with good air circulation by layering. Cover each layer with vermiculite or dry sawdust shavings. Crates can then be stacked in a cool location for the winter. 40 to 50 degrees is ideal. Pump houses and garages work well. 

Tubers should be checked periodically during the winter for any signs of spoilage. If any signs of spoilage are detected, then the affected tubers should be removed and allowed to dry out in a warmer area. Rotted areas are easy to remove at this point without losing the entire clump.

Tuber clumps can be divided in the spring making sure that each division has an 'eye'. Tubers should be planted roughly two weeks before the last expected frost date in a prepared bed. Staking is best done at the time of planting so there is no danger of damaging the tuber later.