Q.Can’t get sweet peas to flower (2 years now), and hydrangea are very late (I think). What am I doing wrong?
I am an enthusiastic novice yet having reasonable success with most species, but not these two .

Certified GKH Gardening Expert
Since both of these are having issues flowering, it could be too much nitrogen in the soil. Feeding an all purpose fertilizer when you have legumes, such as sweetpeas, will halt flowering.
Legumes fix atmospheric nitrogen into the soil, making feeding with nitrogen unnecessary. Make sure to offset this with phosphorus and potassium, in the form of "bloom boosters" at 1/4 or 1/2 strength until you know which plants respond well to it.
These articles should help: https://www.gardeningknowhow.com/ornamental/flowers/sweet-pea/sweet-peas-not-blooming.htm
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-not-blooming.htm