Dahlia Tubers: Dividing and Storage. When you first receive your tubers, they resemble a small long potato. A tuber is where the dahlia receives water and energy to the plant in its early stages of life.
Keeping dahlias at the correct temperature and humidity is most important. In nature, dahlia tubers would over winter in cool, but not frozen soil. The goal when you are storing tubers is to try and mimic these conditions. Dahlias form “eyes” at the crown or shoulder of the tuber. This is the area of the tuber where the stem formed on the plant from the year before. Until eyes start to emerge, it can be difficult to identify where they are located or if there are any.
Dahlias require temperatures above 55 degrees Fahrenheit before they will start to form eyes. Different varieties will also produce eyes sooner than others. Usually after about three weeks. Some take six to eight weeks to produce its first eyes. When we split tubers on the farm, we are normally splitting before eyes are present. Many people, however, wait to split their tubers until the spring when they see eyes forming on them. The key to splitting dahlia tubers is to make sure they you are leaving enough area on the crown of the tuber for an eye to form. This works 90% of the time.
On our farm we use pruning shears to divide dahlias. It is also important to make sure you are regularly cleaning your splitting tools as they can become a vector for spreading disease between plants When storing dahlias, they need to be kept in a cool, but not freezing environment at a relatively high humidity. If your temperature is too high, you risk your dahlia tubers sprouting and growing prematurely. If your temperature is too low, you risk your dahlia tubers freezing. If your humidity is too low, you risk your dahlia tubers dehydrating, causing them to shrivel. If your humidity is too high, you risk your dahlia tubers rotting or getting moldy. The ideal environment to store your dahlia tubers is 38˚-45˚ F and at 75%-85% relative humidity. Mold will naturally form on dahlia tubers in high humidity environments. If you see mold on your tubers there is no need to panic. First, move them to a drier environment. This will stop the grown of the mold on the exterior of the tuber. If the mold is on the outside of the tuber, you can brush it off with a paintbrush or toothbrush. If the mold had penetrated inside of the tuber, you can cut and throw away the infected area of the tuber and let it cut end dry off. Unless very small (smaller than a little finger), cutting away ¾ of the tuber will not affect the growth of the plant. We wash and dry our tubers and then spritz them with food grade peroxide water to prevent mold before storing. Unless mold penetrates the tuber, it will not affect the plants growth. There are many ways people store their dahlia tubers. Some place dahlia tubers in vermiculite or some other substrate and place in a cool part of the basement or garage. Others will wrap cleaned dahlia tubers in a plastic wrap after they split them. We suggest you try different methods and find what works best for you, keeping in mind the temperature and humidity parameters.
We personally store in peat moss.