Peonies are staples in Midwest landscapes. They are long-lived, easy to grow, and reliable garden performers. However, when they do not bloom well, those of us in extension are often inundated with calls, emails, etc. There are several possible causes for failure to bloom. The most common reasons peonies fail to bloom are cultural (planting in too much shade and planting too deeply). Remember that peonies are tough and often survive for many years in not-so-ideal sites.
If the buds do not appear (which is normally the case), some possible causes are:
Planted in Too Much Shade
Peonies need at least 4-6 hours of direct sun to bloom well. It's beneficial to reevaluate the amount of light the plants receive, as it can change over time as shrubs and trees grow and become larger. This is particularly true for long-lived perennials like peonies.
Transplant peonies to a new location with at least six hours of direct sunlight each day. September is the best time to transplant in Iowa.
Recently Divided or Transplanted
Peonies that are moved or divided in late summer rarely bloom well, if at all, the following spring. Sometimes it takes 2 to 3 years for plants to re-establish enough in their new location to bloom again.
Be patient, and flowers will develop once plants are fully established.
Planted Too Deeply
When planting, position peony buds 1 to 2 inches below the soil's surface. Nobody knows how they know if it is 2 inches versus 4 inches, but they do! When a peony is planted too deeply, it may have beautiful foliage but few (if any) flowers.
Transplant peonies, setting them at a depth of no more than 1 to 2 inches below the soil surface. Learn more in this article: Growing Peonies in Iowa: Planting.
Fertilized Too Much
Peonies that receive excessive nitrogen rarely flower well, regardless of site. Nitrogen promotes foliar growth at the expense of flowers.
Reduce fertilization. Learn more about appropriate fertilization in this article: Growing Peonies in Iowa: Care.
Clumps Too Large
Some references state that large, old clumps may not bloom well. However, I have seen several large plants in the Midwest that seem to bloom beautifully year after year. I would imagine that a clump would have to be several decades old before it would fail to bloom. If a clump is considered too large or possibly too old, it can be easily remedied by dividing the plant in late summer to rejuvenate it.
Plants are Too Young
If a clump can be too old, then the possibility exists that it can be too young as well. While most peonies sold are not typically grown from seed, some avid gardeners successfully attempt this process. Plants grown from seed take about 4 to 5 years to mature and ultimately bloom.
Be patient, and flowers will develop once plants are fully established.
Premature Removal of Foliage
Removing plant foliage in July or August will weaken the plant, resulting in fewer flowers.
Leave foliage in place until the first frost. Heavily diseased foliage can be removed when dead, but steps should be taken to address the disease issue for better growth in future years. Learn more in this article: How to Manage Potential Problems Growing Peonies.
Buds Appear, But Don't Open
If buds appear - but fail to open, some other possible causes include:
Late Freeze
A hard freeze in May may damage or destroy the flower buds. Fortunately, this doesn't happen often. Nothing can be done for plants this year. Hopefully, the weather will be more favorable next year.
Other Extreme Weather Conditions
Extremely dry conditions in summer may weaken plants and reduce the number of flowers the following season. Learn more about appropriate care to keep peonies healthy all season long in this article: Growing Peonies in Iowa: Care.
Fungal Diseases
Botrytis blight or other fungal pathogens infrequently attack the flower buds, primarily when conditions are cool and wet. For prevention, the best practices are removing the dead buds in late spring and removing any diseased foliage at the end of the growing season.
Learn more in this article: How to Manage Potential Problems Growing Peonies
Insect Pests
Also, on rare occasions, thrips or other insect pests can damage and distort flower buds and thus reduce flowering. Insecticides are usually ineffective since the damage is often done early in the season.
Undernourished
Low fertility is another rarity in most Iowa soils. Plants that are growing poorly (weak, spindly, yellowish, or "off-color") are not vigorous enough to bloom (but may set buds). Transplanting into a more favorable location and fertilizing lightly after establishment would be beneficial.
Learn more about appropriate fertilization in this article: Growing Peonies in Iowa: Care
More Information
- Growing Peonies in Iowa
- How to Manage Potential Problems Growing Peonies
- Growing Garden Peonies (pdf)
- Transplanting and Dividing Peonies
- Getting Peonies to Bloom (video)
- Gardening in the Zone: Peonies (video)
- Peony Types and Cultivars for Iowa
Photo credits: 1: Anna Merkulova/AdobeStock; 2: Aaron Steil