Dahlias can only be planted in the garden again in May. Before that, you should advance the dahlias. You can read here how it works.It is best to always advance dahlias
Dahlias must be wintered annually in a frost-free room and may only be planted outdoors after the ice saints (mid / late May). However, if you advance your dahlia sticks in a cool and light-flooded room from March onwards, you will achieve more robustness and a more abundant bloom in the plants. Even snail eating is less of a concern with advanced dahlias. So it's best to push your dahlias as described below.
To advance, you must plant the wintered dahlias in a clay pot from March. Only use good substrate! Then you have to put the pots against a window, whereby the room temperature should not exceed 15 degrees. During the advance, you should always supply the dahlias with only a little water.
Relocate dahlias outdoors:
After the ice saints, you can then move the dahlias out into the open as usual. Insert the respective tuber approximately 5 to 10 centimeters deep and, if possible, not or only very slightly. The first flowers then start to form in June due to the head start.
The best way to transplant the dahlias is with the substrate from the pots that you have already used. Simply put this in the planting hole.
Here are a few more articles about dahlias:
»Care and planting time for dahlias
»Multiply dahlias - Here's how