What’s wrong with my peony bushes?

Question

A couple established bushes start to grow, then suddenly the bud and upper stem turns black and dies. This is the second year that it has happened.

The second problem is affecting a couple of bushes that I have had at least 18 years.
This year, most of the bushes grow about half the normal height and only a small portion grew to its full size.

The first picture I attached shows the black buds and stems. The other show the two heights of my older bushes.

This year, we have had a tremendous amount of rain. So much that the soil does not dry out between storms. Does this have anything to do with it?

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Answer 1

Are the plants in more shade than they used to be? I can see in the photo the peony is in shade but the irises are in sun. Peonies need full sun to thrive.
Bud blast causes the black buds and stems and is usually a cultural issue. I've included a link to a care article below. Because of the rain, you may have fungal issues such as root rot going on that is causing the plants to stop growing. Plants normally can't be saved from root rot.

https://www.gardeningknowhow.com/ornamental/flowers/peony/peony-care.htm

https://www.gardeningknowhow.com/ornamental/flowers/peony/peony-bud-blast.htm

https://www.gardeningknowhow.com/ornamental/flowers/peony/how-much-to-water-peonies.htm