When a plant doesn't bloom, it is generally insufficient light. For peonies temperature is often a problem here in S.C., but not for you northern gardeners. Also you might want to enrich the soil with with a low nitrogen, high phosphorous high potassium blend. I once had a clematis that would not bloom. For about three years, blended wood ashes in the soil around the base of the plant, has bloomed like crazy every since. If your plant look lush and green but doesn't bloom, consider my suggestions. If the plant is in denser shade that lightly filtered, consider moving the plant to a sunnier location. If the plant looks sickly, then it could have other issues related to pH, soil compaction, etc. Good luck with the peony.
P.S. - found this via Google
Plants That Fail to Set Flower Buds
If you have a healthy looking peony that sets either very few or no flower buds, it is most likely due to one or more of the following conditions:
A peony is planted at the wrong depth: Peonies are fussy about planting depth. Depth is the distance from the eyes of the root system to the surface of the soil. You can find the eyes by examining the woody crown of the root system when the plant is dormant. The eyes are the large, pinkish-red pointed buds emerging from the top of the woody crown. In our climate, the eye of the peony should be as close as possible to 1 1/2 to 2 inches below the surface of the soil. If they are too deep, flower buds may not form. If they are too shallow, flower buds may be killed by cold. Sometimes plants that started out at the right depth settle or the soil level is raised over time by layers of mulch and the eyes end up too deep.
The peony does not get enough sun: Peonies require lots of sun to bloom well. Sometimes a peony will be planted in full sun and a few years later, surrounding plants have grown and may provide too much shade.
A late freeze: Once the peony starts out of its dormancy in spring, a late freeze can kill any developing flower buds, even if they are still under the surface of the soil.
The plant is too young: Generally, peonies bloom very little, if at all, during the first year or two after they are planted.
The plant is too crowded: Peonies like elbow room. Leave at least a foot all the way around. When they are crowded or have to compete for room for their roots, they may not bloom well.
The plant gets too much nitrogen: Peonies should be fertilized with low-nitrogen formulas. When they are over fertilized or they are planted close to a lawn that gets a high nitrogen fertilizer several times a year, they tend to develop lots of foliage and very few flowers.
The peony was divided recently or moved: If you can avoid it, do not disturb a peony. Peonies bloom best when they haven't been moved or divided recently. When they are disturbed, they may take a year or two to recover.
Plants That Set Buds That Don't Produce Healthy Flowers
When a peony actually starts to form buds that do not fully develop or open, it is usually due to an insect or disease problem. Here are examples of bud problems and how to deal with them:
Botrytis: This is a fungal disease that can ruin a bud as it develops. Botrytis causes a fuzzy gray coating on the flowers and often kills the buds. Botrytis can also affect the rest of the plant. Botrytis thrives in humid conditions and can be avoided/minimized by making sure the peony is planted where it receives lots of sun and has good air circulation. Once the disease is noticed, it is too late to save the buds for that season. Diseased buds should be removed and the whole plant treated later in the season with a fungicide.
Temperatures: When it is either excessively hot or cold, developing peony buds may be killed. This is not a common problem in our area, but it can be minimized by planting mid-season varieties.
Water: Too much water while flower buds are developing may cause them to wilt and die. Try to keep the soil evenly moist and make sure the peony is planted in well-drained soil.