No secrets as such, though we got last year’s crop as small plants from a neighbour (small plants tend to get swapped about depending on who has a surplus of what). We planted them out and left them to it. They produced lovely big roots that we harvested as we needed, only digging them all up when there were signs that local small rodents had found them below ground. In a cool place they seem to last forever. The only reason they don’t do as well for us when we grow them from seeds is that the neighbour we got them from is a retired market gardener who used to sweep up all the prizes in the local agricultural shows and has incredible green fingers.