I have several in pots. They seem to last a couple of years before they give up. Suppose it would help if I made some effort to divide them...... lazy me! LOL!
Stunning I cut mine right down after it finished flowering the first time, now it's just coming into bud again now I asked the guy at the Delphinium stand at the gardeners world live show the other month.....handy advice!! worth it for the stunning flowers. Have you ever tried larkspur....? Only annual, but the same flowers, different folliage.....nice selection of colours....have a look at Larkspur Kingsize Scarlet if you can....stunning colour.
Mine have never really finished flowering. I have had smaller flushes and cut it back, as you said, and am getting more flowers now. Yes I have some larkspur as well. Brilliant plants!!! Am going to grow more next year and try some of the other colors. I have all shades of blue this year so will look out for the one you suggest!