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Tree Peonies

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Picture of a pink tree peony flower.

Picture: the 7 1/2-inch flower on my pink tree peony.

David Beaulieu

Plant Taxonomy of Tree Peonies:

Plant taxonomy classifies the tree peonies with which I mainly deal here as Paeonia suffruticosa. Various cultivars are available, including 'Kinkaku,' which is one of the types that I grow.

Plant Type:

The plants considered here, despite their common name, are classified as deciduous sub-shrubs. Thus, while they share similarities with the better-known peony plants, the two are also different in important respects. The latter, whose Latin name is Paeonia lactiflora are herbaceous perennials. But Paeonia suffruticosa sticks around for the winter, being a woody plant. Both are remarkably long-lived.

Characteristics:

Tree peonies may reach 5 feet tall or more at maturity (10 feet is possible for some types), but they are slow-growers. Growing conditions also affect size. So it is quite possible that your plant will remain relatively small for quite some time.

While their leaves are attractive, it's all about the flowers with these plants, which, as noted above, really are not "trees" at all.

But that's not the only misnomer you may encounter in growing these beautiful plants. I bought a type called Paeonia suffruticosa 'Red,' which is shown in the picture at right. The label even showed a picture of a red flower. But as you can see from my picture, the blossom, while gorgeous, is a pink flower and not at all a true red in color. You'll encounter the same discrepancy with another cultivar: Paeonia suffruticosa 'Zi Qiao,' also known as "Luoyang Red."

As I said, I also grow the Kinkaku cultivar. Kinkaku's flowers are bicolored, sporting a pale yellow color with pink on the edges. Fortunately, my two tree peonies do not bloom at the same time, effectively staggering the color display they furnish my landscape. One year, for example, Paeonia suffruticosa 'Red' bloomed the first week in May in my yard (I'm in zone 5), while Paeonia suffruticosa 'Kinkaku' bloomed the last week in May.

Some types of tree peonies have fragrant flowers, and some don't. The two types I'm currently growing, myself do not (or at least the smell is nothing like the fragrance that my herbaceous forms have). Both among the tree and herbaceous types, there will be differences in aroma based on cultivar selection.

Tree peonies are deer-resistant shrubs.

Planting Zones for Tree Peonies:

Tree peonies can be successfully grown in planting zones 4-8. They are not quite as hardy as Paeonia lactiflora, which is listed for as far north as zone 2. But like Paeonia lactiflora, they are not a plant that Americans in the Deep South have much success growing. Both have chilling requirements, so they grow best in regions that experience cold temperatures during the winter.

Sun and Soil Requirements for Tree Peonies:

Grow tree peonies in full sun to dappled shade. The further south you go in their range, the more sense it may make to grow them in dappled shade. The plants like to grow in ground that is well-drained, with a soil pH that is neutral or slightly alkaline. Plants should thrive in a loamy soil fortified with compost.

Care for Tree Peonies:

The tree peonies you buy at the nursery are typically the result of grafting. The scion is a tree-peony cutting, which has been grafted onto an herbaceous root stock.

Why is it important to be aware of the graft? Well, for one thing, you should plant the graft union at least 2 inches below the soil surface (some recommend more; follow instructions on plant label, if any). This will promote establishment of the scion's root system.

Knowledge of the fact that you are dealing with a grafted plant also comes into play in pruning. Pruning is rarely necessary on tree peonies. But there are two exceptions:

  1. Cut off dead branches
  2. Also prune off branches that are the result of suckering from the herbaceous root stock.

In the case of #2 above, pruning is advisable because you want to promote the growth of the scion, not that of the root stock.

When you do prune, wait till early spring to perform the operation; avoid pruning in fall, as above-ground growth helps shelter the root system in winter. Mulch to provide additional winter protection if you live in an area where the plants are only borderline-hardy.

Like the herbaceous form, tree peonies do not like to be transplanted. So find a suitable home in which to establish them when planting and consider it their final resting place.

Uses in Landscaping:

Use tree peonies as specimens, edging plants or even in hedges.

Outstanding Feature:

The beauty -- including the size -- of their flowers is their most outstanding quality. The flower pictured above right measured 7 1/2 inches across. But as somebody who has always had extremely fragrant types of herbaceous peonies, the two cultivars of Paeonia suffruticosa that I'm currently growing suffer by comparison. But that's why comparison can be such an enemy of human happiness. When I consider my tree peonies simply on their own merits, I judge them to be superb plants, beyond a doubt.

Other Types:

Another popular species of tree peony is Paeonia delavayii.

But even within the suffruticosa species, there is plenty of variety, including different floral colors. For example, Paeonia suffruticosa 'Kinshi is also called the Golden Bird, because it bears huge flowers in a golden-yellow color. While many tree peonies have double flowers, the white Paeonia suffruticosa 'Qing Xiang Bai' produces single blooms.

I've already mentioned the differences between tree peonies and herbaceous forms. But yet another major class is known as "intersectional" peonies, also called "Itoh Hybrids." Think of them as the intersection where the two other forms meet, as they are a cross between the other two types.

Meaning of the Names:

Paeonia, the genus name, derives from the name, Paeon, who, in Greek mythology, was a disciple of the god of medicine, Asclepius (the Roman Aesculapius). The origin of the specific epithet, suffruticosa, may not boast the same pedigree, but it is more useful, being descriptive in nature.

Think of suffruticosa as being composed of two parts:

  1. fruticosa means shrub-like
  2. suf- is really the prefix, sub (meaning "under" or, in this case, "less than"); the "b" mutates into an "f" when it precedes an "f," as in the English word "sufficient"

Thus suffruticosa literally means "sub-shrub," which is how this plant is classified.

Because tree peonies are plants from China (and surrounding areas), you will sometimes see them referred to as "Chinese tree peonies."

The Itoh Hybrids are named after Toichi Itoh, the Japanese grower who originated the intersectional class.


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