Tree peonies flourishing in my cold-climate garden
Tree peonies, also called woody peonies, are plants with breathtaking flowers that immediately capture the attention of visitors in my peony garden. While these magnificent flowering shrubs are often associated with slightly warmer climates, their ability to thrive in colder regions adds an extra layer of colors in mixed borders. In this article, we’ll explore the fascinating world of tree peonies and discover the secrets to cultivating these floral gems in chilly environments.
Embarking on the cultivation of tree peonies in my zone 5 garden marks an exciting new venture for me as a gardener. While I’ve previously explored the world of herbaceous and Itoh (or intersectional) peonies, the prospect of nurturing these plants adds a new layer of anticipation to my gardening journey.
I first fell in love with tree peonies many years ago at the Montreal Botanical Garden, which boasts an extensive collection spread across its gardens, particularly the Flowery Brook and the Chinese Garden.
Additionally, I had the fortune of visiting the Ueno Toshogu Peony Garden in Tokyo, dedicated to Kan-botan tree peonies or winter peonies during 2019.
Paeonia ‘Baron Thyssen Bornemisza’ (suffruticosa) at the Montreal Botanical Garden
I am far from being an expert like some of my friends from my local peony society. My new interest with tree peonies represents a learning opportunity, encouraging me to delve into specific planting techniques, winter protection methods, and overall care practices tailored to these plants. As I witness the first signs of growth and the unfolding of spring vibrant blossoms, I anticipate that this new chapter in my gardening endeavors will not only enrich the landscape of my peony garden but also deepen my appreciation for the diverse and enchanting world of peonies.
Diversity of tree peonies
With roots tracing back to China, where they are known as gānsuǒ mǔdān, tree peonies could well have been one of the earliest plants cultivated for ornamental reasons in history. In Japan, these tree peonies, also referred to as botan, carry rich symbolism associated with wealth, prosperity, fame, and fortune.
While Paeonia suffruticosa, commonly known as the Japanese tree peony, holds a special place in the hearts of garden enthusiasts, the genus Paeonia encompasses a broader spectrum of tree peony species and hybrids. Varieties from other species of Paeonia lutea and Paeonia rockii, and their hybrids have gained popularity for their adaptability to colder temperatures and distinct floral features.
The resilience of tree peonies
Differing from their herbaceous counterparts, tree peonies showcase a robust nature characterized by the persistence of their stems throughout winter. These perennial plants have adapted to withstand the challenges of frost and snow. Their woody stems and sturdy structure provide a robust framework that allows them to weather the chill and emerge with breathtaking blooms each spring.
These peonies usually grow up to 3 to 5 feet in height. Plants may have many stems and may become wider than high. Their floral buds are usually pointy (as in Itoh peonies compared to usual round buds of herbaceous). They are apparent on the fall plant and fatten in early spring becoming big flowers among the first peonies to bloom.
Choosing the right varieties
When venturing into tree peony cultivation in cold climates, selecting the appropriate varieties is crucial. Look for cultivars that are specifically bred or adapted to withstand lower temperatures. Some popular choices include ‘High Noon,’ and ‘Kamata-nishiki,’ known for their ability to thrive in cooler zones.
Planting and location
Proper planting and strategic placement are crucial for the success of tree peonies in cold climates. Select a location that receives ample sunlight, promoting robust growth and vibrant blooms. Tree peonies, compared to herbaceous peonies, are known to tolerate partial shade more effectively. While they still prefer full sunlight for the best flowering performance, tree peonies can adapt to areas with dappled or filtered sunlight. In fact, in regions with hot climates, providing some afternoon shade can be beneficial to protect the flowers from intense sunlight.
It’s essential to ensure well-draining soil to prevent waterlogged roots, especially during the winter months. Prepare the planting hole with loose, nutrient-rich soil, incorporating organic material such as compost. When planting tree peonies, position the graft union (the point where the flowering part is grafted onto the rootstock) at least 4-6 inches below the soil surface. This depth provides insulation and protection against harsh winter conditions, fostering the health and resilience of your tree peonies.
Winter protection
While tree peonies are inherently hardy, providing some winter protection can go a long way in safeguarding them against extreme cold. Applying a thick layer of mulch around the base of the plant helps insulate the roots and retain moisture. Additionally, consider wrapping the lower stems with burlap or using protective covers to shield them from harsh winter winds.
I’ve implemented a careful protective strategy, mulching with wood chips with rose cones for smaller specimens and using rhododendron cones for medium-size plants. I employ insulating envelopes to wrap my few larger specimens and I secure them with anchors. Mulches and protections need to be removed as soon as possible in the spring.
Frost and rain susceptibility
Late frost poses a significant challenge to the floral buds of tree peonies, particularly as these buds start to emerge in early spring. The main disadvantage lies in the potential harm to the delicate buds, hindering their normal development into vibrant blooms. Late frost can cause damage or even destroy the nascent buds, leading to a reduction in the number of flowers that the tree peony can produce during the blooming season. This setback not only impacts the aesthetic appeal of the plant but can also affect its overall health and vigor although next year’s flowering will not be impaired.
Another concern for tree peonies is the impact of rain on their flowers. While moisture is generally beneficial for plant growth, excessive rainfall can be detrimental to the intricate and often large blooms of tree peonies. Heavy rain can lead to the bending or breaking of stems, causing damage to the flowers. Additionally, prolonged wet conditions increase the risk of fungal diseases, potentially affecting the health of the entire plant.
To mitigate these risks, gardeners often employ temporary protective measures, such as providing physical support for the stems during heavy rain and utilizing covers or shelter to shield the delicate buds from late frosts like the little huts at the Ueno Park’s peony garden. These precautions help ensure that tree peonies can withstand unpredictable weather conditions and continue to grace the garden with their exquisite blossoms.
Tree peony protected under a little straw hut in the Ueno Toshogu Peony Garden, in Tokyo
Pruning and maintenance
Tree peonies are often grafted, a horticultural practice where the desirable flowering part is attached to an herbaceous peony rootstock, combining the ornamental features of one plant with the vigorous root system of another. This grafting technique allows for enhanced bloom varieties and increased adaptability. One small disadvantage consists that rootstock may send out new shoots during the growing season. Prompt pruning of these shoots is essential to prevent the rootstock from dominating and ensure that the grafted tree peony maintains its desired characteristics.
Tree peonies typically exhibit pointy floral buds. The presence of a round bud indicates growth from the herbaceous peony onto which the tree peony is grafted. In such cases, the herbaceous peony is considered a sucker and should be removed to promote the optimal thriving of the tree peony.
Below: Pruning the rootstock became apparent when a simple pink flower of herbaceous was taking over the grafted tree peony (yellow flower).
Pruning is an essential aspect of tree peony care, and it’s particularly important in cold climates. Remove all foliage in the fall to prevent fungal diseases but be aware of flower buds. Prune any dead or damaged wood in late fall or early spring to promote healthy growth. Be mindful not to prune too heavily, as this can reduce the number of flower buds.
Fertilization is not necessary; it is preferable to add compost around the crown in the fall. However, refrain from applying mulch, and ensure the surroundings are cleared of weeds.
Most tree peonies do not need staking, but heavy flowers may benefit from individual support.
My budding collection of tree peonies
Apart from discovering a mature tree peony in poor condition in my garden when I moved nine years ago, most of my other specimens have been acquired within the last 5 years. In comparison to herbaceous and Itoh cultivars, tree peonies require a longer time to produce numerous flowers. Consequently, most are still in the early stages of maturity, with some just beginning to showcase their first blooms.
My acquisitions started with Paeonia suffruticosa hybrids. These are most common in garden centers. Because of my lack of knowledge, I planted them only an inch or two below the grafting point. Nonetheless, many bear beautiful blooms each spring.
Four years ago, I also planted the well-known Paeonia lutea hybrid by Prof. Saunders, Paeonia ‘High Noon’, a floriferous hybrid, very hardy and maturing fast. In fact, many imported from the Netherlands tree peonies sold in non-specialized nurseries are mislabeled and turn up to be ‘High Noon’. This is the reason why I now have 3 specimens of this cultivar.
Paeonia ‘High Noon’ in my garden
In the fall of 2022, I bought six more Paeonia lutea hybrids. When I received their bare roots from Solaris Farms in Wisconsin, it was clearly indicated to plant deep, at about 6 inches over the graft point. All of them were 3 or more years old, having been field-grown grafts or divisions. Opting for grafted plants that are older is a superior choice, ensuring a swift establishment and a higher likelihood of successful blooming. In contrast, potted plants typically available in garden centers are usually grafts that are 1 or 2 years old.
Four of my new tree peonies were Daphnis hybrids. Nassos Daphnis, the Greek-American artist (1914-2010), had a unique and multifaceted career, achieving notable success in both horticulture and fine art. His contributions to the world of horticulture includes mostly his involvement in tree peony hybridization. Most of his hybrids bear greek mythological names.
‘Iphigenia’ (photo here), a hybrid created by Daphnis, pleasantly surprised me by blooming with two huge flowers on a 4-inch stems in June 2023.
With a collection of 24 tree peonies, I am eagerly anticipating the blossoming of each one this upcoming spring.
Below are some photos of my tree peonies’ flowers.
Conclusion
Tree peonies in cold climates are not just a possibility but a delightful reality for avid gardeners seeking elegance in their outdoor spaces. With the right selection, planting techniques, and a touch of winter care, these resilient beauties can transform your garden into a haven of floral enchantment, defying the chilly grasp of winter with their timeless allure. Embrace the sophistication of tree peonies, and let their blossoms paint a vibrant picture against the backdrop of a cold and crisp landscape.
With careful selection, thoughtful planting, and a touch of gardening passion, tree peonies beyond the well-known varieties can thrive, bringing a burst of color and elegance to gardens even in the chilliest of climates. Expand your garden palette and discover the hidden gems that await in the world of tree peonies.
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[…] Tree peonies are renowned for producing some of the largest flowers in the peony family. My budding collection includes several red cultivars, originating from both Paeonia x suffruticosa and Paeonia lutea species. […]