I am having trouble with keeping delphiniums over winter. I will sow and plant them and have a nice plant for that year. For some reason they will disappear,root and all, with no trace what so ever. I have a heavy clay soil but I improve the soil every year. Is it because I am using a tender variety?
Slugs will clear them to the ground so they need some protection there.
I have loam-clay soil and they generally do well.
As others have said, you need to establish them in pots for one season, before planting out. I have ornamental bark in my borders, slugs seems to deter the slugs
This year I have bought plugs of blue and white bee? so should I have not planted them this year?
Dependent on variety, some delphiniums only last for 3-5 years max. I treat them as a short lived perennial and have half a dozen backup plants in pots
I love delphiniums but they are a faff at times.