Use lime. Lime is calcium carbonate.

Hi jean, Thanks for the info. If I knew this in the distant past, it was forgotten; it's been sooooo long. Xxx

I am not totally sure that it's needed, based on experience in my garden, though I imagine that it can't hurt. I'd add organic matter, but my soil is acid enough that blueberries, rhodies, cranberries and other Heath family plants do well (and grow wild) and my hydrangeas are blue, but my clematis don't seem to need any soil modification.

I do add wood ashes or lime to the veggie garden because they aren't tolerant of the lower pH, and the local farmer does the same in the field next door, but the clematis don't seem to be as fussy about pH as they are reputed to be.

Here's HF Young:
{{gwi:627128}}From June 8, 2013

and several type 3 clematis, including Arabella, Viola, and Betty Corning.
{{gwi:592640}}From June 22, 2013

Nice to see a Viola pic. Considering that one.

Iris_gal -

In reality there is less pink to the tone of Viola's flower. All the clematis in this photo look a bit pinker than in reality. I really like Viola and have found it easy to grow, though your conditions are so different than mine that my experience may not help you at all. In this photo, Viola is a 3 1/2 year old plant, and in its second season in the ground in this garden.