People sometimes ask me how I grow delfiniums. Not an unique way, just how people do when they grow flowers. I seed some delfinium seeds in autumn ( I used to seed some in spring before ). And transplant them again and again to do #8-#10 size pots or into flower beds. This pic shows the pots I seeded some into last autumn. Depends on each and ever delfinium, some grow faster and some do slower, so some of them still stay in the same pots even now.
Transplanted once into a bit bigger pots. I did it in this spring.
Some that grow faster are already transplanted into #6 size pots. Probably they don't get in bloom this rainy season yet, but may do in autumn. More than 1 year needed for delfiniums to be in bloom after being seeded judging from experience here in Hakuba. In average, let's say 2 years needed for it.
In cool place like Hakuba, delfiniums survive for some years, but they are not strong enough for hot and humid weather, so if it's along the Pacific ocean side western than Kanto region, they survive less than a year. Every year you will find some of them don't germinate, maybe 20-30 per cent of them don't.
If you would like to seed some delfiniums, pay attention below.
#1- Choose when it's around 15-20 C, it's the best temperture for delminiums to germinate, but if it's over 23C, they don't.
#2- Their seeds don't survive long enough.
With reasons above, if you can get some fresh seeds, I recommend you to seed them in autumn. But if you "buy" some from seeds shop etc, probably it's harvested at the previous year, so maybe you are to seed them in spring.