The whole stalk. I cut mine back to just above the main group of leaves near the ground. That's quite a bit but I always get reblooming in early fall when temperatures cool down again. Last year I still had delphiniums blooming on the south side of my barn in early December!!!
This year, I want to collect seed so won't be cutting them back so early. I think I'll still get some reblooming though since they like the cooler temperatures so well.

I have heard that growing delphiniums is extremely difficult. Have you had success doing it?

They're really easy to grow, around here anyway. The proof is old abandoned homesteads where you find them gone wild and blooming without trouble for decades, long after the houses and barns are gone.

The only trouble mine have is powdery mildew, but it's not that hard to control and it doesn't seem to slow them down much at all.

I haven't had any problem growing delphiniums at all. Supposedly they tend to "peter" out after 5 or 6 years but I've had several clumps growing in one spot for 10 or more. One of those clumps didn't come back this spring but I've planted about 20 other delphs around my gardens in subsequent years and so still have plenty. I started several flats of delphiniums from seed this spring and planted out drifts of them in my large garden so next summer should be spectacular!
They were very easy to start from seed.
The only problem I have with mine are earwigs eating the blossoms. They can strip a plant of its flowers overnight. For that reason, I tend not to be able to collect my own seed but have to trade for or buy seed.

I was checking out your trade list and noticed your double yellow and miniature hollyhocks seeds. I will have lupin and columbine seed soon. Interested in a trade?

Sure, it will be another couple weeks yet for them, some of the flowers are just starting to die off. It is a really nice looking hollyhock, and I got it for a dollar last year at Canadian Tire's clearance! Well worth the money.

You've got mail!

I'm trying delphiniums for the first time this year and they are just incredible!! I love them. I bought seed in early spring and started them indoors and I also bought a few that were different from my seeds. My favorite is the sky blue, it was just beautiful. I have left them to go to seed as I would like them to bunch up more in the area they are planted. But I am soooo tempted to cut them back and see those blooms again!

Hello - can someone tell me the answer to this question.

My friend has a huge clump of delphiniums. She would like to know how to collect the seeds - does she wait until the pods turn brown before cutting them off?

AND - she would like to know if the patch of delphiniums an be split.

Thank you for your response

The answer is always yes. Wait for the pods to brown before harvesting the seeds.

I've provided this link for more information on delphiniums. I haven't seen yet the info of splitting the plants although it's likely the answer is yes, the plant can be split. However I wouldn't do any splitting this time of the season which is summer. Best to wait in the fall when teh plant goes dormant. Your friend though can create more plants via cuttings and the procedures are described in this link as well.

http://www.delphinium.co.nz/DelphiniumInformation.htm