I meant to do this post earlier in the year to encourage people to buy dahlia tubers - but then we sold out of them at the CL fair and I forgot until today when I planted up my own tubers.
Dahlia tubers look like mis-shaped potatoes grouped by strings around a central stalk. Every tuber must have a piece of stalk or it will not grow.
The shoots will develop at the join between the hangy down bits and the stem.
Plant the tuber with the stem uppermost into a large pot of ordinary potting compost.
Fill up the pot but leave the top of the stem above the surface of the compost.
Water well and put somewhere warm. I have put mine on a heated mat in the tunnel but on a smaller scale anywhere warm will work. If you put them into the dark make sure you check for sprouts every day or they will become weak and lanky.
Within a couple of weeks shoots will begin to develop. Only when this happens should you begin to water. Keep the plants inside until the frosts have passed and then gradually get them used to outside temperatures by letting them be outside for increasing periods of time