Preparing Tubers.
Before you store your tubers over winter, cut off all the ‘hairy’ roots and remove any loose or damaged tubers. This will lessen the risk of mould to the tuber. In February to March put your tubers into containers of peat-free compost with the crowns exposed to allow the light to get to them. Label your tubers and water in. Set up in a heated propagator or on a heated greenhouse bed. Early in the year extra hours of light via lamps will encourage growth but is not necessary unless you need your tubers to shoot vey early.
Taking Cuttings.
When the new shoots are about 3-4inches you can cut them off below a leaf joint with a sharp clean knife, cut off the bottom pair of leaves then put them in a container of compost mixed with sand or vermiculite. Do not take off any of the tuber because if you don’t, many more shoots will emerge from where you have just taken one, . Many people use hormone rooting powder but my father used to say if you use rooting powder it will root in 2 weeks , if you don’t it will take a fortnight! Try it and see. Water the cuttings and put in a propagator or on a heated greenhouse bench. Water regularly but not too much. Your first lot of cuttings might not take, but keep trying. Once we get the extra hour of daylight with BST it will make a lot of difference. These cuttings will flower and make a tuber in the first season.
Next Steps.
As the cuttings grow, pot on into bigger pots and before planting out, stand them outside for a few weeks in the fresh air, bringing them back in again in the the evening. When all danger of frost is over plant them where you want. Dahlias thrive in most types of soil but do like a sunny spot. They also like a lot of water but its better to water them well periodically rather than little and often. If you are growing standard height plants (about 3-4ft) they will need support with canes and twine. If you want more blooms nip out the first centre bud (stopping) when the plant has about 4 pairs of leaves. This will encourage the side buds to develop. To get longer stems and bigger flowers nip out the side buds on the new shoots (disbudding). Cut off the dying flowers to encourage more blooms (dead-heading) but leave a few on if you want to collect seeds from your dahlias.
May all your cuttings be rooted ones!