Delphinium is a heavy feeders and like well-enriched soil, so apply plenty of compost. Give regular water during growth.
These plants usually do best in mild weather summers. But, there is an exception. The Dowdeswell Delphiniums from New Zealand, called the New Zealand Hybrids.
The Dowdeswell family has bred the new hybrids for high quality cut flowers and for enduring some harsh condition where their growing grounds are. They hold up to winds, heat, and prefer full sun, which is not what the regular delphiniums do.
My first attempt at growing delphiniums was with these. My garden was sunny and hot in the summer. In full sun, I had beautiful flowers in early summer then again in late summer through fall. Sadly, I never thought of taking photos. But I’m planting a second ‘Purple Passion’ plant this year. I would plant many more if I had the space. I might squeeze some in…
So, delphiniums typically prefer morning sun and afternoon shade and overall mild temperatures. If this is close to what you have, you can grow the usual varieties. They take Zone 3-7.
But if you need to meet some challenging conditions, like sun and heat, or winds, go for the New Zealand hybrids. They take Zones 3-10a.
Once the first flush of flowers is over, cut the stems back to 6-8 in. Apply compost, and reduce water until there is good growth again. They don’t like warm wet soil.
You can start delphiniums by seed, but many plants are available from almost all nurseries locally and online