Q.established columbine disappearing
I have a bed of 4-5 yr old columbine that have flourished, blooms were abundant and about 6 ft tall this year, but they seem to be dying. I can find hardly any leaves at the bases of the plants as I trim the stems.
There could be a few different culprits to your loss of leaves on your Columbine plants.
Environmental issues could be a factor, heavy rain or extreme heat and dry conditions.
Have you seen any insects or caterpillars on the plants? Columbine Sawfly can feed on the foliage and strip the leaves very quickly and leave twigs standing much like the image you sent.
If you see the green caterpillars remove them and drop in soapy water. You can treat with Neem Oil.
Trim back the foliage in by half.
I would clean up any leaves that have dropped and dispose of. I would use the wait and see approach after treatment and see if the plants develop any new growth.
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
https://www.gardeningknowhow.com/ornamental/flowers/columbine/columbine-flower.htm
