Peonies are a garden favorite and their big blooms appeal to most everyone. Figuring out what the problem is when they won't bloom can take a little detective work but with some determination you can find the root of the problem and get your peonies blooming before long. This slow-growing, finicky plant is well worth the time invested when the buds begin to open.
Peonies enjoy full sun. While a little shade won't hurt them much, full shade or even shade through half of the day can prevent them from blooming. If your plant developed buds but they did not open or if it bloomed in past years but did not this years, the problem could be nearby foliage. Your plant may have received enough sunlight in the past or earlier in the spring to develop buds. Perhaps a tree or large shrub has filled out with leaves or has grown larger and now blocks much of the light from reaching the peony. Trim the offending foliage if possible otherwise you may need to move the peony to a sunnier location.
If you use fertilizer and your plant is thick and bushy but not blooming, you may have over-fertilized. Water the peony thoroughly to rinse away excess fertilizer and cut back on further applications. If buds develop but do not open, it could from a lack of nutrients. Top dress or add to the top of the soil around the base of the plant a layer of compost. Do not cover the crown.
Peonies are very slow growers and take several years to adjust to a new location. Whether you plant new ones or transplant, it can take three years before the plant bears blooms. Peonies can be divided when they grow too large. However this dividing causes the same reaction. The more sections the root ball is divided into, the longer it will take for each section to recover and produce blooms. A good rule of thumb is not to move or divide more than once every five years.
Peonies do not like to be buried too deeply. This can happen when planting a new peony or when dividing an older one and planting the smaller sections. The eyes of the plant should not be more than 2 inches under the ground. If they are deeper, you will need to dig them and replant them to the proper depth.
The roots could be in competition for soil nutrients from a nearby tree. In this case the peony will have to be moved. Another source of root problems can come from moles or gophers. Protect your peonies by installing a wire mesh barrier around the bed in the soil.