Your one peony may have verticillium wilt. It's a soil-borne fungus, so if you lose the plant, be sure to dig up surrounding soil and discard. Mulch looks rather heavy.

Thanks for the tip. Do you mean the mulch might be too close and heavy around the peony, or in general?

Around the peony.

What has changed in your garden since last year? I agree that your mulch is too close. Is it a colored mulch or a natural mulch I can't tell from the pic? Did you dig up the 'dead' one? If so, what did you find? Did you insert the circle cages in the Spring or have they been in at the same spot since planted?

It's black coloured mulch. I added new soil this year. It was bulk soil 1-yard delivered to my house from a popular sod farm many people in the neighbourhood/city use. My other plants seem to really like it. I put the cages on when they were about 2ft high. I haven't done anything different...I don't think. Could they both be ant related? I didn't see any on the one that's dying only the one whose buds didn't bloom, but I did see a lot of very tiny black specks on the stalk I cut off and wondered. I will clear the mulch back from being so close to the plant and see if that helps anything. Thanks.

I agree with Nancy your plants may now be too deep. See picture attached - the eyes should be no deeper than 2". I prefer keeping them 1"-1 1/2" to allow for the plant sinking. Also the ants should not be an indicator that anything is wrong. Since you added 2 different elements to your garden the same year you're seeing problems it may be that one of both are the problem. Like you said you'll move the mulch back that should help. Are the rest of your gardens doing well with the same topsoil and mulch? If so, then you know that's not the problem. Will you be digging up the plants in question? Perhaps they are just having trouble adjusting to the crazy weather we've had this year. As the season progresses you may see nice foliage. Every thing you do will be to improve the situation for next Spring.

Ants on peonies is normal. They are attracted to the sweet sticky stuff that covered the buds. I agree that your peonies are probably too deep. Something similar happened to me and I now make sure I do not cover the peonies with too much mulch.