APPARENTLY I’M the kind of person people give tree peonies to, because over the years I have been gifted four of them by four different people. Call me the accidental tree-peony gardener, I guess–one who is long overdue for a 101 on their history, their pruning and other care. That’s what I just got from Jeff Jabco of Scott Arboretum at Swarthmore College in the horticulture-rich Delaware Valley of Pennsylvania.
Jeff is Director of Grounds and Coordinator of Horticulture at Scott and Swarthmore, where among the extensive and diverse plantings is a whole Tree Peony Garden area, one of the first collections established after Scott was founded in 1929 and now including more than 80 varieties of tree peonies. He is also vice-president of the Mid-Atlantic Peony Society.
Why consider these plants? Tree peonies are deer-resistant, extremely cold-tolerant, long-lived and really don’t require a lot of complicated pruning. And oh, those flowers (that’s one of Jeff’s favorites, ‘Nike,’ up top.).
Read along as you listen to the April 10, 2107 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Spotify or Stitcher (and browse my archive of podcasts here).
At the bottom of the page, learn about visiting Scott Arboretum at peak moments for tree peonies and other outstanding gardens and plant collections there.
tree-peony q&a with scott arboretum’s jeff jabco
Q. I’m so glad to finally get the lesson I am way overdue on. [Laughter.]
A. And it’s not too late.
Q. It’s never too late. I do try to be nice to them. Does that count?
A. That certainly counts; they are very forgiving.
Q. Before we get into tree peonies, as a bit of a scene-setter: Tell us a little about the Scott Arboretum.
A. The Scott Arboretum is at Swarthmore College, so the entire college campus is around 400 acres. About 125 acres are intensely managed, and the Arboretum surrounds all of the academic buildings, administrative buildings, residence halls—so the Arboretum really surrounds people who live and work at the college and our students every day.
Q. A lot of plants.
A. A lot of plants, yes. Mainly the Arboretum originally started with woody-plant collections, but over the past 25 or 30 years we have focused more on garden situations—so space between buildings, and courtyard gardens. So besides being a place to grow and display the best plants, to inspire home gardeners here in the Delaware Valley, we can also teach them about plant combinations, and good garden design also.
Q. I think I read somewhere that you have 4,000 different kinds of plant growing there on the campus; it’s probably even more now.
A. It probably would be more, if we kept track of our herbaceous plants.
A. All of our woody plants are mapped and catalogued, with computer records for all of them, and we’re just in the very, very beginning of starting to do that with herbaceous plants.
Q. You have really noted collections of flowering cherries, and crabapples, and so many things—lilacs, magnolias and more.
A. Yes, so as well as the old tress that have been growing here on site since the college started in 1864, the Arboretum started in 1929. So that was when the real collections idea started, with getting the various collections of plants so people could kind of compare one to the other and see which ones they liked for their home gardens.
Q. As I mentioned in the introduction, the tree peony collection was one of the early collections in that effort. Maybe we should define what a “tree peony” is, because it’s not just one species, correct?
A. That’s correct. “Tree peonies” is really more of a misnomer, because they are more shrub-like than tree. But I guess they get the idea of being “tree” because they are a woody peony. So if you would treat these peonies like you would for most of the peonies that people are familiar with—the herbaceous ones—and cut these to the ground every winter, you would never get flowering at all, because they flower on old wood.
Q. Good thing I didn’t do that. [Laughter.]
A. That’s the Number 1 thing to learn: If you have a woody peony, you do not cut it to the ground in wintertime.
Q. Taxonomically speaking, where do we place these? Are they called a particular group, or do they have a Latin name that encompasses them all or what?
A. It’s funny, because as with most taxonomic things, it’s a real confusing thing. It all depends on which botanist you listen to and believe. It’s confusing also because these have been cultivated for hundreds and hundreds of years. There are records from the Chinese that go back into the first several centuries AD, of these plants being grown in a garden setting.
A. And before that they were used medicinally—but they have been used as garden plants since very, very early centuries AD. What they basically come from are several different species of woody peonies from the mountains of China, so they all originate from there.
Over the years, these were crossed back and forth, and crossed back and forth, so over the time it has become fairly complicated as to what actually they are. There are several species that are recognized that they are probably hybrids of.
So there was an original Paeonia suffruticosa—and many times if you look botanically, that’s what all tree peonies are listed as: suffruticosa, or suffruticosa hybrids.
Q. So instead of—what is it, Paeonia lactiflora, the herbaceous peonies?—gardeners would say “these are the suffruticosas” and “these are the lactifloras,” like it was black and white or A and B. But it’s not that simple?
A. Right—and botanists group all the herbaceous ones into a subsection of Paeonia and then a couple of different groups in there, and under the genus Paeonia for tree peonies, they have a subgenus of Moutan, which is actually the Chinese name for tree peony.
Q. It sounds puffy: moutan. It sounds like a big puffball to me; I don’t know why. [Update: When I got home from the recording studio, I remembered: The homonym “mouton” refers to sheep fur that has been made to resemble that of seal or beaver, hence my association with the word.]
A. It would probably be easier if we called it something completely different than just peony.
Q. So they have been cultivated since early centuries AD, as you said. I mentioned herbaceous peonies, and haven’t some of the woody ones and herbaceous ones also been crossed to make even further confusion?
A. Yes, and that’s a more recent thing. Basically those are a cross between different sections of the whole genus of Paeonia, so sometimes they are referred to as intersectional hybrids, but more recently they are called Itoh hybrids, because a gentleman by the name of Itoh from Japan was the first one to do this cross between a tree peony and a herbaceous peony, a Paeonia lactiflora.
These are very interesting plants that are really in fashion now. They are still relatively expensive because they are still new, but they do have that hybrid vigor, so they grow very fast.
What they do is they have the form and the substance of a tree peony—very large flowers, and in the color range that tree peonies come in—but the stems die back to the ground in the wintertime.
So you’ll get this big shrub, kind of like you would for herbaceous peonies; it can tend to be very rounded and full, and they want the same types of growing conditions as herbaceous peonies do, but they will die to the ground in the wintertime. They make excellent cut flowers and are a really beautiful plant.
Q. Wow, there is a lot going on. [Laughter.] I think I have some of those, too, by the way—I think Roy Klehm, a friend and one of the people I associate with the genus Paeonia, has gifted me some new invention of his. When I say invent obviously I mean breed and introduce. He has sometimes sent me surprise packages. [A flower cut from one such intersectional gift, above.]
I think I mentioned when we were emailing back and forth, that I have one oddball species that someone else who is a peony lover—Tony Avent of Plant Delights Nursery—he said to me once in a conversation that the most-underappreciated woody peony was Paeonia ostii [below]. So is that a tree peony?
A. That’s also in that sub-genus of Moutan, as Paeonia suffruticosa, and some people list that as a sub-species of suffruticosa. Another one like that is Paeonia subspecies rockii, or Paeonia rockii, the Joseph Rock’s variety. Some people are familiar with rockii from that.
Some of those species are wonderful. And a couple of other ones: One that’s pretty common in England is lutea, Paeonia lutea, and that’s a small yellow-flowered tree peony. And delavayi, and that’s a dark almost kind of brownish deep red-maroon color, is another species. So many of those have been some of the parents or greatparents or great-greatparents of our more modern tree peonies that we have.
Q. So it’s the big gene pool.
A. It’s not a huge gene pool. Depending on who you talk to there can be anywhere from five to maybe 12 species that are in that section of Moutan, or the tree peonies.
Q. Among tree peonies: What’s the range of colors, and plant sizes? How does that work?
A. If you kind of get away from the whole taxonomy-nomenclature side of things, many times tree peonies are listed by color, and sometimes by form of the flower, and sometimes by the form and shape of the plant. It can kind of get confusing to people who are not familiar with this at all.
So color range is really wide: They go from white, and you can have pinks, yellows, true reds, you can go deep reds and maroons, and you can go into lilacs. You can go into many colors, except there is no green and no true blue—but everything from purplish-reddish that’s very deep, and the literature calls it black but it’s really a very deep maroon—all of those ranges in colors.
You can have multi-colors in the same blossom, so it might be like in rockii, where the deep center of the petal has a dark flare. You can always tell something that has rockii in its background, because it’s deep purple down at the base of the petal.
Q. See, that’s what I love—where you see the hints of the genetics.
Q. And that’s what I love about people like you who can say, “And that’s where you see that, Margaret.”
Q. That’s what’s so cool, when you start to recognize something, and the next time I see it I am going to remember that you told me this.
A. And actually there is a whole group of those rockii hybrids. We have very few of those in Europe and the United States, but the Chinese really love them. We had a fellow visiting here from China, and he gave me his new book that’s all on these rockii hybrids.
Q. Besides the colors, you mentioned the form of the flower. I think of them as being tissue-papery or crepe paper—these big flowers. What’s different?
A. If you think of something like a dahlia or a chrysanthemum, you can have single-flowered, you can have semi-double, you can have double. But it goes beyond that because in a single flower; if you look, its parts are very visible in there. Sometimes the male part—the stamen—can turn into something almost like a petal, which they call petaloids. Those might be a different color, or be much smaller than the true petals, so you can have all these kinds of variations.
And then you start getting anemone-flowered type, or bomb-flowered type, or thousand-petaled flower type. Actually the Chinese get very, very creative and they group it into something like 24 different groups based on flower type.
Q. Oh my goodness. That’s a lot. [Laughter.] We won’t have a quiz on that; not on the air.
Q. And then the stature of the plant is another category?
A. Yes, based on the stature of the plant. You can have something that can be lower and spreading; I’m thinking of something that might be 2 or 2-1/2 feet tall and kind of spreading to 3 or 4 feet. You could have something that’s more of an upright, rounded shrub, anywhere from 3, 4, 5, 6 or 7 feet. Or you could have something just upright and relatively narrow—like 2 to 3 feet wide, but up to 6 or 7 feet tall. Some of these plants at maturity could get to be 8 to 9 feet tall, if they’re very old and in a very ideal situation, and you give them 40 or 50 years.
Q. I don’t think I have 40 or 50 left to give them, sorry to say. [Laughter.] But I can be optimistic and plant for the future. So let’s talk about caring for them. What do they want to be happy (besides 40 or 50 years)?
A. All peonies, whether you’re talking herbaceous or tree or the Itoh hybrids, all want good drainage. That’s the Number 1 thing. If you plant them in an area that’s too wet, they are going to suffer, and the roots are going to rot, and they will be very unhealthy looking and not perform well for you. Number 1 thing is to give them good drainage.
When it comes to sun, the herbaceous types really want as much sun as you can give them, so I would say at least 8 hours of sun a day.
Now for tree peonies, they also like sun; the more sun, the better they are going to flower, meaning the more flower buds are going to set. But with tree peonies, the blossoms are more delicate, so they would ideally be planted in a situation where they get morning sun and late-afternoon sun, but get some shade in the heat of the day. They’re going to be flowering in the Delaware Valley near Philadelphia, for us here, anywhere from late April to probably the third week of May, depending on the cultivar and what species they come from. Many times we have really intense sun—the first intense sun of the year—at that time. The flower will bloom, but they just won’t last as long. Everyone has probably seen pictures of tree peonies growing in Japanese gardens, and they have little umbrellas over them, and that’s why.
A. They’re shading them from the sun, and the flowers will last a lot longer.
Q. So I need to get a lot of umbrellas; I will put that on my shopping list.
A. The Japanese paper umbrellas.
Q. In the Tree Peony Garden at Scott, how is this perfection achieved? I assume you do not cart out the umbrellas each day.
A. No, we don’t do that. [Laughter.]
Q. You don’t have one special gardener who is the Umbrella Master.
A. No, unfortunately we don’t have that much staff. Our collection has changed locations several times over the years, and while we have tree peonies represented throughout much of campus, there is one main area that is our Tree Peony Garden.
It’s on a south-facing hillside, so it has really good drainage. It’s good soil and we worked up the soil initially. At that time, you do want to check pH, because peonies don’t like to have pH that is too low, which is more of an issue here in the Eastern United States. You want something that is more between 6 and 7.
What we have is couple of older trees: a red oak and a very old ginkgo. Just so we stay away from the base of the plant, and we’re not competing with the roots too much, the peonies are ideal in situations like that. These are really tall trees, and they give that high, dappled shade that the plants really like.
Q. But they don’t get baked, and you don’t lose the flower so quickly. Do you feed them? And you said they need good drainage but are they thirsty? What else?
A. For the most part once they are established, they are very drought-tolerant. In the areas they originate from in China, they have extremely dry summers. That said, the plants will be a lot healthier if you don’t let them get into moisture stress in the summer. So really the only time we would water them is if we get into a dry spell in summer—if we have hot temperatures, and haven’t had a good rain in two weeks, then we would put some water on the tree peonies. Other than that, they are not particular; they just don’t want to be in an area where the soil is too heavy and wet.
As far as fertilizer requirements, we worked in a good amount of compost to the soil in the first place, and we try to do things for the most part as organically as we can. So we’d use an organic fertilizer, and we’d be applying that in late winter, just as the growth is beginning to start.
Q. If people were looking at a brand, one that people know is Espoma that’s high in organic content, and it has Holly-tone, Rose-tone and so on. I’m not doing an ad for them, but I know that’s one people are familiar with. So which formula?
A. I would go with something like Rose-tone; you wouldn’t want Holly-tone because that would reduce the pH.
Q. So a rose fertilizer would be the approximate formula you were looking for.
A. Or if you were non-organic, I would use something like 10-10-10.
Q. A balanced fertilizer.
A. And for a mature plant, if you are using something like 10-10-10, you would probably use half a cup or three-quarters of a cup spread out all around below the plant, scattered all around maybe a square yard or so.
Q. I want to talk about some favorites, because there are a lot of them to choose from. [Laughter.]
A. There are; we have a lot. I was doing a little bit of calculations here, and we have almost 300 peony plants here, and very few of those are herbaceous; most are woody. We have about 164 taxa of plants; about 120 taxa in the woody ones. So we have quite a few, and a very good representation of Dr. A.P. Saunders, who did his work in the early years of the 1900s, and he was in Upstate New York. So peonies are very, very cold-tolerant—and almost deer-resistant, too.
A. So there you go: Deer don’t like them and they can handle cold. These plants can grow up into Minnesota, so very cold conditions—certainly Zones 3 and 4.
Q. Do you have any personal favorites? [Above, ‘Chinese Dragon’ tree peony in the Scott collection.]
A. Yes I do. There is a Japanese one called ‘Ren Kaku,’ which is a beautiful white and a low grower, so kind of a low spreader. It will get about 2 or 2-1/2 feet tall and has a beautiful just pure white flower.
There is another Japanese one that is a brilliant, brilliant red. It is called ‘Kao,’ or you can sometimes see that spelling different ways, like ‘Kaoh.’ That’s a beautiful one.
Some of the newer hybrids: There is one called ‘Gaugin,’ as in the painter, that is beautiful—and talk about a big blossom that looks like crepe paper. I would say the background color is kind of apricot, yet it has some yellow in it and it has a red picotee edge and a little red veining through the petals.
Q. Oh my goodness.
A. And another one similar to that is called ‘Nike’ [photo at top of page], and that is by Nassos Daphnis, a Greek artist living in New York City who did this hybridizing.
Q. As a sideline.
A. Yes, as a sideline.
Q. Oh, good; I’m glad to know because it’s a little overwhelming if one wants to pick a couple to add to the garden. It’s like wow, wait a minute; which ones?
A. At some garden centers, you can find ones that are just listed as red or pink or white, and I would stay clear of those. Many times those are from older Japanese or Chinese types that had really big blossoms, blots of petals, but when they bloom all the petals point down and flop down to the ground—or just hang below, so all you are doing is looking at the back of the flower.
jeff’s tips on pruning and planting tree peonies
TREE PEONIES don’t require much pruning, says Jeff. The most important regular task: In early spring, prune the tips of the stems back to expanding buds. It is natural for tree peony stem tips to die back over winter.
The shoots that held the flowers can also be removed, in summer, just above the new growth. Caveat: If you want your plant to set seeds, wait until the pods have formed and ripened, in fall, before this deadheading operation.
If the tree peonies grow leggy, some stems may require removal at the base to bring them back to a fuller form—as with the rejuvenation of more familiar garden shrubs.
And two other tips:
Most tree peonies are propagated by grafting onto the roots of an herbaceous peony. Sometimes, in the first few years after planting, Jeff says, shoots of the herbaceous peony might grow up, too. As these are noticed, try to break them off by gently pulling the herbaceous shoot just below the soil level. This should separate the herbaceous shoot from the root system.
The ideal time for planting, lifting and dividing, or moving any peony (herbaceous, Itoh hybrid or tree peony) is in the autumn–typically September and October. If this is done in the spring, it may take the peony several years to recover. This is due to the fact that the majority of peony roots grow in mid to late autumn.
more about scott arboretum
THE SCOTT ARBORETUM at Swarthmore (in Swarthmore, Pennsylvania) is a must-visit for plant lovers any time of year. Other major plant collections include: flowering cherries, crabapples, hollies, lilacs, magnolias, tree peonies, rhododendrons, hydrangeas, conifers, vines, summer flowering shrubs, viburnums, and witchhazels.
- Visit the Scott Arboretum website and search the plant database, garden maps and more.
- Browse all the gardens and collections
- Calendar of upcoming Scott events
- Or create your own tour from suggested ones on the website.
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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 10th year in March 2019. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the APril 10, 2017 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify or Stitcher (and browse my archive of podcasts here).
(Photos except yellow intersectional flower and P. ostii courtesy of Scott Arboretum; used with permission.)