To plant them, dig a hole at least 20-30cm square and around 20-30cm deep for each one. Cover the base of the hole with 10cms of compost, or manure and give it a good dousing with a full watering can and then plant the dahlia at a depth of 15cms. You may need a stout stake, not just a bamboo cane, to support each plant and it is a good idea to knock this in first and then place the plant by its side. Plant in a sunny spot and keep moist yet well-drained. It will need to be lifted in winter - once the foliage dies back simply dig it up and store in a cool, frost free location.