There is no single right method for storing dahlia tubers over the winter. The goal is to dig healthy plump tubers in the fall and keep them dormant for months without moulding, rotting or shrivelling. So why isn't there a single best method? Every grower has a unique set of environmental conditions that determines which methods will work best. There is always some amount of storage loss. Ideally, this is less than a few percent... So what storage conditions affect success:
Humidity of the storage area: if too low, tubers will shrivel. If too high, moulding and rotting are more likely.
Ventilation in the area: The more ventilation one has, the more drying that will occur. Less ventilation leads to more stagnant air circulation which increases chances for mould and rot.
Temperature: Below 0 degrees C or 32 degrees F tubers freeze or die, above 10-12 C or 55-60 F they may start to wake up from dormancy and sprout.
It is your ability to manage these three environmental conditions that will determine success in overwintering your dahlias. Of the three variables, temperature is usually the easiest to control for most growers. Tubers stored between 7 and 10 C or 40 to 50 F should do well and stay dormant. Ventilation is a bit trickier for most growers, but venting and fans can usually be used to more air and prevent excess humidity. Humidity is much more variable from region to region of the country and in different storage environments.
Most of us will need to put our tubers in ventilated or sealed containers with some sort of medium surrounding the tubers to maintain them. Here is a partial list of containers that have been used:
plastic storage boxes with or without lids
plastic grocery bags
zip-top storage bags
paper bags
cardboard boxes
wooden crates or trays
milk crates
Styrofoam boxes or coolers
Do you need ventilation via permeable material like wood crates and paper bags or holes in plastic bins? Plastic bags may be left open or closed. Your humidity and ventilation will determine what method will be most successful.
The medium provides an environmental bugger around the tubers shielding them from possible periodic changes during storage. Some mediums that have been used include:
vermiculite
perlite
sawdust or wood chips (may draw moisture)
sand (must manage moisture content)
peat moss (must manage moisture content)
garden soil (must manage moisture content)
if your current storage method is successful, there is no need to change. If you feel you are experiencing less than ideal results, we would suggest trying a few different methods in moderation to see what works best. Remember, there is no single right method to store dahlia tubers over the winter.