Putting a lot of work into something and then not seeing the results you expected is the worst. Many gardeners do everything they can for their peonies only to get no blooms and to be left wondering what could have gone wrong. Most of the time, the reason the peonies didn’t bloom is something simple that got overlooked.
Too Much Nitrogen for Peonies
If the peonies are established and have bloomed before, then this is the most likely cause. Over-fertilization is probably the most common mistake gardeners make. There are several options to remedy this, but probably the easiest is to fertilize with something that contains no nitrogen (a P-K mix for example). Another option is to lightly till and “drill” the soil around the plant.
Taking care to avoid the roots, “drilling” wide holes into the soil can cause much of the nitrogen encountered to release into the atmosphere. It also allows for easy access to add in fertilizers without tilling.
Above all, take care not to over-fertilize, especially in the month or so before blooming season. Most of the time, peonies really only need fertilizer in the spring (in a standard flower or 10-5-5 mix) and a good compost and mulch covering in the fall.
Not Enough Sunlight for Peonies
Getting them more sunlight will probably require that you either renovate other landscape elements or move the peonies themselves. Transplanting is likely the option you’ll choose.
Late in the fall, around September or later, after the plants are dormant, is the best time to transplant. Cut the peonies all the way down to near ground level. Dig around them in a relatively wide circle (roughly the diameter of the original foliage) and down as far as possible to preserve as much of the root system as you can. Remove and place in their new location quickly. Remember: peonies need full sun and well-drained soil. If you wish to divide plants, now is the time to do so.
Improper Planting of Peonies
Many plant their peonies too deeply, which “stunts” the plant and requires it to catch up before it will bloom. Most likely, improperly planted peonies that are still growing will bloom the following year.
When planting a peony, the hole it is placed in should be wide enough to accommodate the root system and no deeper than the top of the roots where the stem begins. Putting the plant in too deeply runs the risk of it not being able to grow high enough to sprout leaves in the spring and get a good, early start.
If planting in the fall (recommended), cover the peony with 4-6 inches of mulch and remove the mulch in the early spring after the first major thaw.
First Planting of Young Peonies
Peonies newly-transplanted or that are new in the ground will only occasionally bloom in their first year. So if you just purchased peonies and planted them and have not seen any blooms (but the plants appear otherwise healthy), you’ll likely just need to care for them as usual and wait another year.