Board Thread:General Discussion/@comment-108.160.18.134-20160606210409/@comment-96.19.217.236-20160822185246

In the material edition, the part entitled Salvia, it does discuss Suguha's birthday, but it never actually says when it is. What it does say, however, is that Kazuto planted a lot of blue salvia flowers for her birthday:

"......Seven years ago...... On Sugu's birthday. You wished to gather a lot of Salvia to get its nectar, so I bought some seeds with my allowance and planted them at that vacant lot."

Unfortunately, it seems that that variety at least blooms from spring through fall usually, as the lady who lives there said that a lot of them bloom in the spring, and that in November the flowers fall off. So, I think that we can be sure that Suguha's birthday is not in the winter, and probably not too late in the fall, but that seems to be about all that we can draw from this part...