Drive stakes into the ground when you plant the dahlia tubers. If you wait until the dahlias are growing before you put in stakes, you risk damaging the tubers. Pound the stake until about 12 inches of the stake is underground. This will ensure the stake doesn't fall over under the weight of the dahlia.
Tie a piece of string tightly to the stake at one foot intervals along the stake. Leave enough string free to tie loosely around the dahlia's stem as the flower grows.
Tie the first piece of string loosely to the dahlia stem when the dahlia is about 1 foot tall. Leaving the string loose helps you avoid pinching off the stem.
Continue to tie the dahlia as it grows, adding one tie for every foot of growth.