Dalphs are easy to grow from seed, although you can keep splitting larger ones to multiply. Any multi-purpose compost will do - simply sow into a tray & cover with 1/4" compost. Germination is 2 - 3 weeks. Keep moist. Ideal time to sow for next year's plants is June - Aug (as this allows the plants to get a good root structure before the winter when they will become dormant). We have always found a late sowing gives the plants a great start for the following year rather than starting to sow in March etc. Prick out & pot up at just over 1" - suggest into 3" pots. You will need to re-pot on again later into larger ones which will last them for the winter & until you plant out next year. Continue to water them so they produce growth this year, but gradually cut this down again as the autumn / winter develops & let them dry out. They are very hardy plants & you can either leave potted up somewhere sheltered over winter or plant into the ground covering their crowns. We usually leave potted up in the pollytunnel. Remember that all growth will die down anyway and new growth & shoots will start developing from the spring, hence why it is better to sow now rather than waiting until March. Give a good feed with MiracleGrow in the spring & start watering. They can be planted out when growth is getting established - would suggest you take precautions to eliminate the slugs though - they will chomp a whole stem in a night. You might want to check out the pics of our Dalphs which we sown this way & are only 1yr old - Good luck.