Apparently, it's what is wrong with your site.
I'd guess it's a water or nutrient issue, with water being most likely. Probably too much of it would be my guess.

I live on top of a hill and the ground drains well . Is it possible that the full sun could be the issue ?

Not to disagree, dbarron, maybe it could be the drainage. I keep them mulched to keep the grass down around them . What about making a raised bed six inches high and moving them into that ? It sounds like peonies don't like wet feet

Well, it's not the sunlight, and it's not (according to you) the depth (and I've found they will adapt and situate themselves as they like anyway to some extent), and I would seriously doubt it's nutrition. It must be water (that being about the most common thing).

Derby42,

You do have a problem that is hard to figure out, age, disease, nutrition, and site all affect a peonies growth rate.

I grow many peonies, they love full sun but do not like wet feet and will rot, sort of like a potao tuber, but that said, a flower bed that drains well is good enough for them they don't like a constantly moist place. The depth of a peony is one inch below the soil surface, deep roots will not bloom.

However you said they formed buds which then die, this leads me to think that botrytis could be the cause. But without seeing them it is hard to tell.

I would not make another bed for them unless your were sure that moisture is the culprit.

Maybe I will take some photos this spring and post them here.

Peonies won't bloom if planted too dep. Are you sure the eyes of your peonies are planted less than 2 inches deep? Deeper than that, the peony will suffer. Mulching in the summer is ok but you must pull the mulch away in spring when the peony starts to grow.

When I dug them it was early spring and the eyes were just poking up through the soil. I cut around them and took them all out in one solid mass. When I got them home I took a shovel and cut them into three equal pieces. They remained intact with the soil that I dug them in. I dug three holes just deep enough to fit each of the pices in. I did not put any fresh dirt on top of them, just set them in the holes and firmed up the dirt around the edges. They come up later and grow slower than other peonies in my area. When other ponies are blooming they will be short and have small buds the size of a pea. The small buds dry up. I think it made one flower once. Then as it starts to get hot and dry in the summer the plants wilt and dry up. I water them some but they just decline all summer.

No Wonder! You divided and transplanted the peony in spring during its active growth phase. Peony roots do not like to be disturbed during this phase. When they are disturbed, the plant suffers from severe transplant shock and therefore its growth is stunted. But don't worry, they won't die. This spring, you will see significant improvement over last spring but I am not sure if they will recover enough to give you blooms.

KarenPa, I transplanted them four years ago and I see no improvement yet.

I second what Karen said. You described classic symptoms of peony transplant shock. It was not only dug out but chopped into pieces in a whole wrong time of year. Traditionally peonies are being transplanted/divided starting in August and even then plants will need some time (a year or two) to recover from that treatment before they bloom. Inappropriate time of digging/dividing can set plants back for four to five years and it seems that is exactly what you are experiencing with your peonies. Give it more time and it will bloom again after it fully recovers.

Sorry, I miss that. Given the amount of time of 4 years after transplanted, they should recover already. If you do not see any improvement this year, the only thing you can do is to dig them up this fall and examine the roots. Are they showing any signs of rotting or tangling? Trim off all bad parts. Replace the soil with new soil and if drainage is a problem perhaps you need to make a raised bed and plant the eyes of the peonies no more than 2 inches deep. I have peonies foliage withstanding 90+ degrees in my zone in full sun without wilting. Where are you located?

South west missouri

It sounds like I should have done a little research on when to transplant them.

Derby42, don't feel bad. We all make mistakes in the garden plus sometimes certain chores must be done outside of their perfect time frame.
I have a question about how you divided your peony. Did you dig it out, cleaned all the soil to expose all roots and than carefully examined where the emerging eyes are and where to make cuts through the root ball? Peony is not a typical perennial in a way you divide it. It's not only a matter of slicing a piece off with a shovel like you would do with hosta or epimedium. And it does take a little practice. I'm asking about this because everything else you provided for your new plants seem perfectly OK: full sun, fertile soil, good drainage, right planting depth, room to expand. That's why I'm leaning towards serious transplant shock.
I would leave it in the ground until August or September and if it still doesn't start recovering by then I would dig it out and inspect the roots.

Enith, I just cut through it with the shovel making three equal pieces. There were many emerging eyes and I just made sure there were several eyes on each piece.

Hi Derby, I've dug, divided and replanted peonies in the spring after they've started growing multiple times before--it should've only impacted their growth that same spring. The fact that it grew back at your mom's and bloomed already certainly indicates that the pieces you planted should've, also.

Spindly and weak stems could indicate too much shade--you said they're in full sun. Also could be planted too deep but you already said your replanted at the same depth (I'd make sure it wasn't more than 2 inches deep, though). You said the root was around a foot across, how deep was the plug that you took out? A peony of that size should probably have feeder roots that should've been around 18 inches deep. If you didn't get enough feeder roots to support the growing eyes your plants could still be recovering. Also could be getting too much moisture from being in water retentive soil, they hate wet feet. Are you in a humid area? Could they be getting mildew from watering too much on the leaves? I wish we could offer a sure fire solution but without seeing the roots and where/how they're planted we can only guess based on our experiences.

If your plants are getting sun and are not in really wet soil I'd just give them a good, organic fertilizer, maybe the bulb booster one Kousa recommended last summer, when they start growing this year. Water at the ground as needed while they're actively growing. Established peonies don't need a lot of supplemental watering--they're actually quite xeric. I normally only water mine in the evening if I see them drooping, they'll perk right back up that same night. If you get a lot of buds you might want to think of pinching some of them out, just to give the most likely bloomers a better chance of making it to full flower.

As your peonies emerge this spring please post pictures, maybe someone will recognize a problem that you can easily resolve. I'd certainly try the fertilizer, judging from her beautiful pictures of peonies last year the one Kousa uses works well. And if this is the spring that they make it to full bloom just because it's the right time we all like to see pretty peony pictures, anyway!

Thanks everyone for all of the good advice.

Lisbest1, it is possible that I did not get enough feeder roots. The soil where they were growing in at my mothers was extremely rocky. The plug I took out was about a foot across but only about eight or ten inches thick, less around the edges because when I dug them I angled the shovel in under them as I cut around the clump.

If they came back at all you got enough for them to survive! That's the biggie and they'll recover. Hopefully this will be their year to make you glad you did the work to transplant them!

Thanks again for all of the advice from every one. I have only recently discovered how helpful these forums can be.

When I've had peonies form buds which then fail to develop, it's either because they're infested with botyris, which if you google it, is pretty easy to diagnose, or because their water supply was inconsistent during the growth phase in spring / early summer. Later on in the summer, after they've bloomed, inconsistent watering doesn't seem to matter so much, at the very worst, they will just go into hibernation early.

I googled to see what it looked like. I don't recall them having anything that looked like that. The inconsistent watering could be another culprit.

Doesn't anyone else think it could be not enough water during the growing season? OP wrote:

"I live on top of a hill and the ground drains well."
"The small buds dry up. I think it made one flower once. Then as it starts to get hot and dry in the summer the plants wilt and dry up. I water them some but they just decline all summer."

All I know is that my peonies stay green and never wilt until fall when they yellow and go dormant. Once I had sprinkler troubles that affected one peony, and it did get a bit wilted with yellow edges, which is what alerted me that there was a problem. I remember the next year it had a lot less flowers than usual. ....So have you checked to see if water is sinking in well enough?

Hi Derby, Do you use miracle grow or other water soluble fertilizers, or granular fertilizers on your peony? If so, the nitrogen from these fertilizers are too much, which will give you lots of leaves and no blooms. Only use 1 lb of bone meal per plant in the fall. This should get your blooms back, If it is because of fertilizer.

I guess inadequate moisture can be a problem if OP lives in a very dry climate. Unless he has his plant under a roof overhang or under a tree where rainfall cannot reach, then I can see the plant has an inadequate moisture problem. But he did not note that. My mother's peonies had grown well eventhough she never watered or fertilized them. The only other thing that I can think off that may affect his peony growth is the ph of the soil. I wonder if it is too acidic or too alkaline.