For a fertilizer to change the pH it would depend on the components. Some can change it downwards and some upwards or no effect (would depend on the amount as well). Some daylilies find a neutral pH too high and you've had interveinal chlorosis on the newer leaves which suggests either iron or manganese deficiency. I've had micronutrient problems with mine at 6.8. A range of 5.5 to 6.5 was recommended by someone who did some formal research on daylily nutrition although it would also depend on other factors. Some daylily cultivars seem to need more acidity than others. Rhododendrons can also vary, while most need a distinctly acidic soil there are some that will tolerate a higher pH. I don't know which ones you have there but we have a couple of rhodos here that grow and flower on a soil that is barely on the acidic side of neutral.
I wasn't suggesting a pH value would be on fertilizer bags but it may be given for compost. I don't know what the conventions or rules are there in Italy. Here to be classified as a fertilizer it must show an NPK analysis.
