Hydrangea macrophylla 'Enziandom', sometimes sold in this country under the name 'Gentian Dome'. It is usually referred to as the "deepest of all the blues".

Not only is it a true, deep blue in my acidic soil, but it produces very large flowerheads. This was the very first hydrangea I bough for my new garden this spring - it was a "must have" now that I have a sufficiently shady property!! Mine is still just a baby and not the one shown in the linked photo but I expect it to look like that soon :-)

Mopheads Blue Prince, Enziandom, Generale Vicomtesse de Vibraye, Hamburg, Marechal Foch and Nikko Blue are recommended by Glyn Church in the book Hydrangeas.

Thx for suggestions. Any experience with Blue Danube? Photo is of H. aspera 7' - 8' and unknown blue macrophylla 4.5' we had at last house. The blue is not Nikko Blue, which was lighter in color and taller growing behind this one (not shown). Best guess so far is Mathlida Gutches. I added Aluminum Sulphate and we had acid soil there in PNW.

Opens like this.

Nice picture. So are still now in an acidic heaven kind of place?

Reminded me of pictures I once saw from someone -maybe the name was livinez or something like it- That person had created a blue garden with plants (hydrangeas and others) that bloomed blue. Very cool.

These blues were along the front more partial sun area of our shady yard. They called us the Hydrangea House locally.

Not in acid soil heaven at next house. Can't depend on soil pH being right

in many cases. So use Lime, Super Phosphate, or Aluminum Sulphate to adjust colors. Bark over the top can help keep things acid over time. If you don't broadcast the treatment evenly, I get 'horrible uneven color consistency' like this ... which can make me quite happy. Mathlida Gutches here, so don't need to buy LA Dreaming to get color range, unless want less color intensity, and to not monkey as much with soil amendments!