How tall are they? They may have been bare-root plantings, which take about three years for any blooms to appear, they MAY be planted too deep, I wouldn't fertilize them too much, in fact I don't fertilize mine, I just have very good amended soil, and I mulch. Peonies are slow growers to begin with, you may have to watch them again next year, and then make a decision.
I have many that I planted bare-root, and this will be the first year for blooms on many of them, I'm excited to see them. Good luck.

Well, I didn't plant them, and no one lived here for years before us, so I'd say they're at least 10 years old. The ones that I noticed and fertilized a little last year are about two feet high and bushy - a few others that I just noticed this year are just a couple stems with a few leaves - maybe six inches high or so. We figured out that we have them about every twelve feet down the driveway.
Our soil is super sandy and doesn't hold nutrients very well - that's why I foliar feed my veggies so much.

Do they get full sun (more than 6 hrs/day)? How close to the driveway are they?

Here is a link that might be useful: The bottom of this page seems to address all your questions

My suggestion would be to haul in alot of compost, and get your soil properly amended, it makes all the difference for the health of your plants. It sounds like they're pretty close to being fully developed, if they aren't getting enough sun, they won't bloom, they just develop foliage.I'd check the depth of the planting too. If they're more than three inches, it's too deep and they won't bloom, you could divide the others if you wanted to, but I'd do that in the fall.

I second primgal 's advice. Peonies are usually pretty tough but they do need water and full sun. Especialy water before they bloom. Being planted too deep lots of time is the culprit. Some of mine nearly have roots on top of the soil. I do dig mine earlier since I'm a zone 3 and feel they need a little more time to become established before Winter.Do yours get good snow cover? Good Luck !

Thanks guys. I guess I'll dig them up and replant them shallower later this summer and see what they do next year. They have full sun, I water them quite a bit and I've also been fertilizing more besides adding a slow release fertilizer around them. They're about 10 feet from the driveway with a bit of ditch in between.

My peony bloomed two years ago but hasn't for the last two years. Why?

I suggest redigging them in the fall. That is the best time to do any digging of peonies.
not more than 2" deep. Dig carefully as the roots may break off of the eyes . I dug out my Barzella last fall and it took hours, lost quite a few roots though. Go easy..

Peonies generally do not need very much fertilizing.

Good luck!
Lynn

I've been told (by a nursery owner) that peonies like a little bone meal. It should help encourage blooming. I haven't tried it yet, but plan to put a little around my 2nd and 3rd year peonies this year.

Mine had buds but they wilted and all was left was leaves. Why?