KFredenburg said:Do you have any idea as to why it hasn't?
JBarstool said: I grow Philadelphus here, though not Belle Etoile. I find it reliable though it would prefer a bit more summer moisture.
Do you prune the shrub - if so how and when (generally blooms on previous years wood)? And, at 25 years, what is its approximate size (if it is mature age yet still not fully sized might indicate conditions less than optimal)?
Do you have access to leaves in the Autumn? As you are clearly a v e r y patient gardener (waiting 20+ years for a bloom) a thick mulch of shredded leaves/leaf mould will eventually help.
Going out on a limb here as you seem to be describing pretty lean, not very moisture retentive conditions and adding organic matter by mulching will slowly improve structure and moisture retention. Generally they like well drained (seems you have this one covered) but moist soil. I don't think of them as very hungry plants. Water the plant well and then apply a thick mulch, As it breaks down and is transported downward by worms top it up as needed.
Consider a summer hair cut this year - cutting 1/4 of its old growth to ground.
Too bad you can't smell mine, he said gloating... a new experience for me, trust me, there's very little to gloat about in my garden.