AMONG SHRUBS, the most common ones I hear people wondering aloud about are hydrangeas, hydrangeas, and more hydrangeas. But when it comes to questions about perennials, herbaceous peonies top the list. To help us learn more about these extravagant, long-lived bloomers, I called peony expert Jeff Jabco of Scott Arboretum at Swarthmore College in Pennsylvania. Jeff is Director of Grounds and Coordinator of Horticulture there, and an officer of the Mid-Atlantic Peony Society.
Learn from him when and how to plant them for best results; which varieties stand up to wind and rain best without toppling; how to have a peony season that extends to about seven weeks of beauty, and even when to cut flowers and prepare them to be longest-lasting in a vase (that answer may surprise you). And yes, he’ll explain why those ants like peony buds so much.
Read along as you listen to the June 10, 2019 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).
The photo of Jeff below is by Rutgers University, which gave him a major award not long ago for his “unsung hero” role in horticulture. Here at A Way to Garden, we like to sing about Jeff, too. (We also like coral-colored peonies like ‘Coral Charm,’ above.)
herbaceous peony q&a, with jeff jabco
Margaret: Yes. How has the peony season been there in your region?
Jeff: Actually, it has been a really, really nice season, up until the past couple of days [at the end of May], when we had some very severe thunderstorms.
Jeff: But we’re really at the end of our season. We had great flowering, and the flowers really seem to last a long time for us, so that was very nice.
Margaret: Do you attribute it to lots of moisture and cool weather, or what?
Jeff: Yes. Well, I think part of what it was… Yes, we had lots of moisture last year, and, just so peonies were planted in the right spot, it didn’t affect them. And actually, it probably helped them a bit. It was a good winter. It wasn’t exceptionally cold, and peonies are very cold-hardy anyway, so that wouldn’t affect them.
Jeff: We didn’t have any really late frost. Sometimes, the peony shoots will start coming up in spring, and if we have a really extreme cold period at that point, then we can get a little tip dieback. But that didn’t happen this year. And then, when peonies started flowering, the temperatures… At that point, we didn’t have lots of rain, so it was relatively mild or just a very light rain and not excessive humidity, and some bright, sunny days, and then cool nights. So the peonies just lasted for a long, long time.
Jeff: The worst thing to have is the peonies just starting to flower, and then you’ll get 88 or 90 degrees for a day or two and really intense sun, and the peonies last two days, and that’s it.
Margaret: I know. So disappointing. Now, last time we spoke on the show, we talked about tree peonies [above, some of the tree peony collection at Scott Arboretum]. But what we were just speaking about, we were going to talk about herbaceous ones today, and what you were just speaking about kind of leads us to the basic 101 that I’m eager to get from you, and I know people want, and sort of creating their happy place [laughter]: siting and planting and aftercare. So, why not to give us some of the details or sort of the cheat sheet on making herbaceous peonies at home?
Jeff: Sure, sure. Well, first off, just to clarify about herbaceous peonies, these are probably the more popular peonies and the ones that people are most familiar with. A lot of times, it was used as an old-fashioned pass-along plant because you can have peonies last for 100 years or more. There are certain ones growing in gardens that have been there for 100 years. No one’s ever divided them or fussed with them or whatever, and they just keep coming up every year and flowering.
So, there’s a great, old-fashioned plant. But also, it’s a group of plants that there are some really active hybridizers. So, for decades now, there has been a lot of work going on in the U.S. and elsewhere around the world with hybridizing the peonies. And they’ve been a cut flower, kind of a mainstay cut flower, for June weddings and late May for a long time.
Margaret: So, this is Paeonia lactiflora? Is that what we kind of…
Jeff: Yes. So, mainly. I mean, there are some herbaceous peonies we call the hybrids which have some other species. [Above, ‘Christmas Velvet.’]
Jeff: They might be a little shorter, might flower a little earlier, but the main season, and the ones that people are probably most familiar with are the lactiflora hybrids.
Jeff: Yes. So, that is a species native to the far reaches of eastern Russia and then down in through China and Korea, so they’re Asian, Asian species.
Margaret: O.K. So, siting them and, you know, so you could… what are sort of the optimal conditions? Yes.
Jeff: Well, the optimal condition would be, Number 1, good drainage. Peonies do not like to be in a wet site, so whether you’re talking a tree peony, a intersectional hybrid peony, or the herbaceous peonies, they don’t want to be in a wet site. The herbaceous peonies want sun, so at least six hours of direct sun every day. If they are getting too much shade, the plants won’t be as vigorous and they will not flower as well.
So that’s one of the common things. People say, “Oh, you know, I have a peony and it used to flower well and it doesn’t flower well anymore.” And I say, “O.K., has the water conditions changed?” And if they say no, then I say, “Well, what about shade? Has a tree grown over that area so that it’s more shaded?” And that’s usually the Number 1 culprit for a peony not flowering so well any more, or not being very vigorous. So they do need to have the sun.
Jeff: Yes. The other thing about planting is, typically, when you buy peonies, the ideal time to buy them and plant them would be in the autumn. So usually peony growers would be digging their peonies in very late summer, so usually in September time, and then they would sell them dormant and as a bare root. They may be packed with a little bit of peat moss in late September through October.
And as soon as you get them, you want to plant them in the ground. You want to prepare a site that is maybe 2 feet across and about a foot deep, compost in with it. Once again, make sure it’s in a well-drained site that’s going to be in the sun, and to give it a little start, you can use some bulb fertilizer, because you want to use something that’s now in nitrogen. So a bulb fertilizer, you can go the organic route, which would have a lot of bone meal and potash in it, or you could use a chemical fertilizer, but you don’t want to overdo it. So for a bulb fertilizer maybe half a cup or so, quarter to half a cup for that and mix it into the soil.
And then you lay the… what would be… it’s a thick fleshy root, so it almost puts you in mind of a very thin carrot, and it’s usually darkish-brown on the outside, and then if you cut into it it’s kind of a yellowish or creamy yellow or white on the inside of that.
Margaret: But we’re not going to cut into it, right? [Laughter.]
Jeff: And then, at one end where it’s thicker, you’ll see several buds, and the buds really look like the tip of your little finger, so they’re kind of pinkish or maybe whitish or maybe have a little brown skin over the top of them, but they are about the size of the tip of your little finger.
Jeff: And that’s where the shoots are going to grow up in the spring.
Jeff: So, at that point, you want to plant that so that those buds are 1 to 2 inches below the finished soil level. So you plant your plant with these roots kind of spreading out to the side and then cover it so that there’s buds or 1 to 2 inches covered with soil.
Margaret: O.K. And that’s-
Jeff: And for that first year just put a light mulch over it for the winter, then in spring you just peel back a little bit.
Margaret: And that depth thing, is a “thing,” isn’t it, with peonies? Because they can sulk if they’re too deep. Can’t they?
Jeff: Yes. Right. So if you plant them too deep they’re going to suffer because it’s too hard for the shoots to reach up to the top. And if you plant them too shallow, then the crown of the plant is really exposed to harsh conditions in the wintertime. So, the planting depth is pretty important about that.
The other thing, at the time of planting, if you are planting into an area where you have low pH, and a lot of our areas in the Eastern United States are low pH, you want to put some pulverized limestone in with them at the time of planting.
Margaret: Oh, interesting.
Jeff: So, if your soil typically is in the range of a pH of 5 to 6 or something like that, about 1 cup of pulverized limestone in your hole mixed into that.
Margaret: Huh. So, now this is an investment. You said they’ve been known to live 100 years or whatever. Many people have or may buy an old house, and it has peonies that probably have been there for 30 or 50 years or whatever from a previous owner. So you’re saying, prepare well because these are going to go the distance, these plants.
Jeff: Yes. They’ll be there a long time.
Margaret: This is not a marigold.
Jeff: Right. Right. Exactly. And most likely, you’re not going to be digging these up and replanting them. I mean, you can, once they get bigger, you can dig them up and divide them and share them, or you’ll get a couple more plants out of it. But you don’t have to do that. If you do a good job of preparing the site, the peony is going to be there for a long time.
Margaret: And if you ensure that the tree limb doesn’t grow over it and shade it. [Laughter.]
Jeff: Right. Right.
Margaret: Yes. Yes.
Jeff: So I mean that’s basically what you do for the time of planting. Now, I do know that probably most of the peonies that are sold every year are sold in the springtime and they bloom in May when you see them coming up or they’re in flower and the garden centers have them, and what I tell people is like, “O.K., you buy it because it was an impulse thing. You see it in flower and you really want that one.” So, you have two choices. Either you can keep it in that container and then hold it until fall, but just make sure you do not overwater it if you hold it in for the summer.
So, still put it in a mainly sunny location or partly sunny location, don’t let it go dry for long periods of time, but don’t overwater it, and then when we get to be September, knock it out of the pot. You can cut the stems off because they’re finishing up by that point, and even if they are a few green leaves, it’s not going to really give it much more energy to the root. And then knock the potting soil off that’s in the pot, and then plant it just like you would if you had bought a bare root.
Jeff: The other option is, if you really want to plant it into the ground, you don’t want to disturb the roots. So, basically, you’re going to knock it out of the pot and plant it, just with minimal disturbance to the roots at that point. And the big reason for that and the reason that we divide and plant the peonies in the fall is right after a planting in the fall, so that period of mid-October through November or up until the ground freezes, that’s when those thick peony roots are putting out really, really fine little white feeder roots, and they don’t do that in the springtime.
Jeff: So, if you get your plant divided and planted in the fall, then you’re going to have these good new feeder roots that are going to nourish the plant. And if you do all that planting in the spring, you don’t have any of those roots that are going to be coming on until the fall.
Margaret: Right. So, I’d love to encourage people to have a longer peony season over all because a lot of gardens, you know, people say, “Oh, I love my peonies,” and they point to the one that they may have, and maybe one of the big, kind of puffy, late ones, or… And I think, “Gosh, you know, we should all go to the specialty catalogs and look at the extra-early, early, middle, late whatever.” Because, how long can we have… And I don’t know if you want to include some of the non-herbaceous types or whoever you want to include in this, we’re going to have peonies for a long time in our garden if we choose correctly. Yes?
Jeff: Right. Right. So, just say here, for our location where we are, we can have peonies start flowering in mid-April. Sometimes it’s an early year, maybe even the second week of April, but usually it will be around the middle of April, and they’re going to continue probably until the second week of June. So the main peak of herbaceous flowering is just finishing up now [note: taped May 30, 2019]. Some of the Itohs are… they’re a little bit later and so they kind of wrap up the season. And then there’s some very late herbaceous ones in their peak right now, too.
So, really, I mean with your selection of peonies, you could go five to six, maybe even seven weeks, depending on the season. But if we get that hot spell in the middle of all that, then it’s just going to shorten the season a little bit.
Jeff: And there are all different types. Even if you’re just staying with herbaceous, there are descriptions to say when they’re roughly going to flower. They’re not going to give you a calendar date, the kind in peony bloom season. They usually… and actually if you go and you look at the catalogs or you go online and look at the places that sell peonies, descriptions are always very good about the time for flowering. Because, remember, the main reason that a lot of people started growing these was as a cut flower.
Jeff: And so people were selling them or using them for themselves, so they wanted to have something earlier, something around Mother’s Day, or something that’s going to be happening around graduation or wedding time in June, or something like that. So usually they’re listed as very early season, then early season, then midseason, and then late season.
Margaret: Not unlike daffodils, you know.
Jeff: So you have to prepare one to the other that way.
Margaret: Yes. Like, the same as if you look in a daffodil catalog, a specialty catalog, they’ll group them for you. And if you just get one variety, you’re going to have a week or so, and if it’s 90 degrees, you’re not. [Laughter.] If it’s 90 degrees you’re not.
Margaret: And then the color range and the form range is… Yes.
Jeff: Well, one other thing about the peony season, there are some peonies, herbaceous peonies, that when the stem comes up there’s going to be one flower on the top of each stem. And then there are other ones where it’s going to have one main flower but then they’re going to have some side shoots or side flower buds.
Typically, what will happen, is that main flower will open up and then a week or so later, then the side buds will open up. If you do a good job of deadheading, you know, you don’t even see the old large blossom, but then you have these other later ones coming. They will be a bit smaller but they’ll also be a week later, and it still can be a very attractive plant by selecting ones that will do that. That’s another way to kind of extend the season, with the same plant, by selecting ones that will do that.
Margaret: And I think… I was just going to say, it’s the forms and color range. I mean, it’s not just big puffy fully double pink things, there’s an incredibly extravagant range of flower forms and colors. [Above. ‘Karen Gray’ peony.]
Jeff: Oh, yes. And I think it probably one of the things that has done peonies more of a disservice than anything, are somebody’s really old pass-along ones. You know, their beautiful, beautiful color but you get a light shower in early May and-
Margaret: Flop. [Laughter.]
Jeff: ... the blossoms just collapse to the ground. And then that’s what you have the rest of the season.
Jeff: So, and those were some old ones that people loved the blossom, and those were the ones that were selected for cut flower. So those would have been grown in nurseries and usually what the nurseries did, the extras that they had, that they didn’t need any more, they would sell. And so that’s where people got them, or gave them away or whatever.
But in growing them in a nursery for cut flowers, they would usually stake them, or you have them in some kind of system where they’re going to be staked and kept upright. And you know, they have good stems but, if they get a lot of water in them from rain or too strong of a wind, then they just collapse to the ground.
So those are not some of the best ones, unless you’re prepared to stake them.
Margaret: And so, with ones that are planted properly and grown in six plus hours of direct sun, do you think we don’t need the peony ring or the grid, you know, or do we? Do you use a support there, at Swarthmore?
Jeff: No. No, we don’t, and some of ours fall to the ground if we have wet weather. I wish we had time to stake them, but we don’t. But, if someone’s like, “O.K., I love peonies but I don’t like how they flop,” the best thing to do is to go online to the American Peony Society website and there is a section called Awards, and if you look under the awards, there’s something called Award of Landscape Merit, or ALM.
Now these are peonies and they’re probably, every year there are a few more that get added, so they’re probably up to 30 or more peonies on that list now, and these are ones that have good strong stems, they hold up well in a landscape, they don’t need staking. And if there’s anyone that really likes peonies or wants to get started in peonies, I’d say, “O.K., pick one of these. These are the ones you should start with,” because you don’t have to worry about staking them. And that, I think, is the main thing that really turns people off with some peonies, is the staking.
Margaret: Now, just take a minute to talk about… I love some of the early, little guys that are herbaceous but they’re not lactiflora, like… I don’t know if I’m saying it right, mlokosewitschii, Molly the Witch, or obovata, is that right? Sometimes I make up names, Jeff. [Laughter.]
Jeff: Yes. Yes.
Jeff: Yes. Paeonia mlokosewitschii, or sometimes called Molly the Witch, yes. [Molly, above, at Margaret’s.]
Jeff: It’s a very nice yellow-flowered peony. It’s pretty rare, so it’s not that easy for people to find that one, but it really is a beautiful plant, and can be really, really long-lived. When it comes up, the foliage looks more like tree peony-like foliage, but it truly is a herbaceous plant, it will die back to the ground every year. And for me that is going to flower before any of the other lactiflora–
Margaret: Me, too.
Jeff: … herbaceous peonies are going to flower. So for me, it’s flowering around tree peony time, which is a bit earlier, so usually that’s late April, early May, for me.
Margaret: So we could add to our peony palette, we could add even some of the little woodland peonies, like that.
Jeff: Yes. And the woodland peony’s very, very nice. The woodland peony, it’s a peony that wants to grow in shade. And all the others I’ve been telling you, they want sun. But the woodland peonies, and so sometimes these go by the botanical name of Paeonia obovata, or Paeonia japonica. And depending on which botanist you listen to, sometimes it’s Paeonia obovata sub-species japonica. [Laughter.]
So, the whole thing is really, just a little difference in what the hairs on the leaf are and how tall they get. So usually the japonicas are ones that are around 20 inches tall, the obovatas are a little bit taller than that. The obovatas can be a very, very light pinkish-purplish blush to the white, where japonicas are going to be white. And you know, like you say, they stay relatively small, they flower in the shade. They are a single-flowered peony, the blossoms don’t last very long. I usually think if a blossom on those last three days, it’s lasted a long time.
Margaret: Oh, but they’re so beautiful.
Jeff: They’re very fleeting, but they’re beautiful-
Margaret: Oh, they’re so beautiful.
Jeff: ... in a shaded woodland garden.
Margaret: Yes. They’re beautiful.
Jeff: And the nice thing about those, they are as easy as anything to grow from seed.
Margaret: Yes. I even get self-sowns.
Jeff: And actually, the seedpods are beautiful.
Jeff: The seedpods are gorgeous. Yes. So you have these, you know, several carpals and when they mature in the summer they open up and the background of the pod where the seeds are is a bright pink and then the seeds are this bluish-black. And I used to try to collect them, but the squirrels on my property love them and they plant them for me.
Margaret: Yes. And I get self-sowns, yes.
Jeff: And a year or two later, they pop up in the beds. They pop up in the lawn. And they pop up in the lawn before I do the first mowing of the lawn, so I… and I recognize what they are now. It looks like a very tiny little peony leaf, and so, I just, with a little trowel, pop them out of the lawn and then plant them into the garden.
Margaret: Yes. Who would have thunk self-sowing peonies.
Jeff: Yes. And so, right now, I have dozens, dozens in my garden now-
Margaret: Yes. Yes. It’s exciting.
Jeff: …thanks to the squirrels planting them.
Margaret: So, in the last couples of minutes, few minutes, I wanted to ask you about, if we go back to the floral kinds or the lactifloras, if we want to use them as cut flowers, say we have a few that we want to put in a cutting-garden area, what’s the best time and way to cut them that makes them last? What’s the protocol there?
Jeff: Oh, O.K., great topic—and actually our local peony society, the mid-Atlantic Peony Society just had our last official spring gathering the other night, a members’ garden tour, and we had a peony judging. So, because we are at the end of the season we were telling people that if you want to enter some flowers into the judging, what you do is, when the flower bud starts to show color, so you’re going to see the petals there but it’s not open yet, just lightly squeeze it with your two fingers, and if it feels like a marshmallow—you know, the large campfire marshmallows, you make some S’mores out of-
Jeff: ...if it feels like that, that is the stage where you cut the stem, O.K.? So you cut it off at the length that you would want, and then you wrap it up in newspaper. You just roll it up in newspaper and put it in the refrigerator. Just dry, like that.
Margaret: Dry newspaper. Oh.
Jeff: And then… Dry newspaper. Yup. And put it in the refrigerator, and then, you can leave it in there for days. You can leave it in there for a couple of weeks, and then you take it out, recut the stem just a little bit from the bottom, you cut an inch or two from the bottom, put it in water and then within one to two days it will be open fully for you.
Margaret: And this is the trick that the cut flower growers… Because they can’t afford for their whole crop to suddenly, if 90 degrees are coming, right? Or, you know-
Jeff: Right. Right.
Margaret: ... they can’t afford to have a wholesale loss. So this is what they do, I think.
Jeff: And if you order peonies by mail, that’s what they’re doing. They’re cutting them at that stage and shipping them to you, telling you, “Oh, when you get them, just cut the stem and just put it in water and in a day or two they’ll be blooming.” Or, to have all these peonies for June weddings, you know, not everyone’s growing these in the far North, so they pick them earlier, they keep them, wrap them up, keep them in their coolers, and then they just take them out a couple of days before and they’re all set.
Margaret: How about a quick 30-second question I forgot to ask. What about the commonly asked one about, “I have ants on my peony flower buds.”
Jeff: [Laughter.] Yes. A lot of people say, yes, “So, what’s the deal with the ants and the peonies?”
Jeff: And they think it’s a problem. You know, if you see herbaceous peonies, when the buds start to swell, there is this covering over the bud, a little green leafy little structure that covers the petals, and they exude a sweet, sticky material there. So the ants are just there getting a free meal.
Jeff: So even after the buds open, there’s still a little bit of that… so, it’s like a nectar. And so they’re there getting that nectar, and so peony flowers do not need ants in order for the flowers to open, I hear that tale-
Margaret: I know, right? [Laughter.]
Jeff: … No, no, has nothing to do with it. The ants are there to get a free meal and that’s all that it is.
Margaret: Well, Jeff Jabco, you’re the best, and thank you always for just enriching our knowledge and enthusiasm about peonies. I’ll give lots of information with the transcript to the show about visiting the Scott Arboretum and about events that are coming up and so forth, but thank you so much.
Jeff: Thank you, Margaret. It was really fun. [Below, ‘Golden Angel’ peony with Amsonia.]
more about peonies
- Jeff Jabco and I talk tree peonies
- Award of Landscape Merit peony list
- The Scott Arboretum website
- Visiting Scott Arboretum
- When the normally tough peony fails to bloom
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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 June 10, 2019 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).
A couple peonies in my brother’s garden (Rochester, NY) have some stems that fall to the ground and are partially broken at the soil level. The stems might survive but they’re surely unattractive and worrisome. What’s the cause? They are in bright sun, sandy soil, not much water. Could it be the soil needs compost? Or is the soil depth built up by fussing around them so the roots are too deep?
Love your website & your podcasts, and congratulations on your NY Times book review – great!! I can relate to the ‘bossy’ comment… my parents and friends called me ‘the general’ when I was six and beyond because of my ‘take charge’ attitude myself…LOL!
Best of luck, I look forward to you every week!
Thanks, and regards,
How much sun do peonies really need? J have several on the east side of my home that cannot get more than a couple hours of direct sun because of all the trees to the east.
I am glad you mentioned the woodland peonies and how easily they self-sow. Come to think of it, my herbaceous peonies were grown from seed that I got at a rock garden meeting in Pittsburgh years ago.
Hi, Bill. Six hours of direct sun minimum is the recommendation…The peonies will grow in a more shaded spots, but will be mostly green with many fewer flowers.
I really wish peonies lasted all summer. i just love them and we have some oldies in our yard. I feel bad for flicking the ants off my mother’s peonies when i was little. I would also pop her hosta flower buds. I was such a little gardeners’ nightmare as a youth.
Hi My question is what happened or caused my Peonies to turn from the beautiful bright red/purple color to white?
And I did get more blooms but after the blooms the leaves turned very mild dew.
I planted a bareroot peonie three years ago that was supposed to be white with dark red center. Bloomed for the first time this year and the flower was white with a light cream center. Was the plant mislabeled or can the lighter blooms vary season to season based on conditions? All my others are dark, so I’d appreciate anyone sharing their experience.
Hello! This was, as usual, so interesting. I just wish there was more on the ant subject. I knew about the honeydew and I’ve always used the presence of the ants as an indicator of which tiny bud was viable. But what I REALLY want to know is how to convince those ants to leave when I want to cut the flower, not after I bring them inside and they march all over the house? I don’t even cut them any more because of those darned ants. And I don’t want to use some horrible spray. I tried submerging them in water for a few hours but the ants persevered and were able to march around the house anyway. ☹️
Are you supposed to dead head peonies? Or cut back the foliage in the fall?
First let me say that your podcast makes my looong commute if not outright enjoyable then at least much more bearable. I look forward to your podcast every week! I paid particularly close attention to your podcast about peonies and have a question about planting site:
I get that peonies like sun and should be planted accordingly. However, I have a location that gets full sun all Spring and well until the peonies have finished blooming. Then the area becomes shaded once a large sycamore tree leafs out. Would I get okay blooms in such an area or do the peonies need full sun even when they are not in bloom?
What goes on with plants that flower (including spring bloomers like daffodils and peonies, which are two good examples) is that after they’re finished flowering, the leaves do the work (utilizing sunlight) to store energy to produce next year’s flowers. So…peonies will probably bloom a bit in such a spot, but lightly. They won’t be loaded with flowers because the leaves can’t soak up the maximum sunshine in that key time after flowering but before winter dormancy to prep for next year’s bloom phase.
Thank you for your prompt response. That makes perfect sense and I really should have known that – I guess I was just preserving the slightest bit of hope that it might work regardless :-)
No need to post my response on your website – I just wanted to thank you. And thanks again for such a wonderful website/podcast. I recommend it to every gardener I know!
What about growing peonies in pots? Can you give me some tips on the best way to do this, please?
Hi, Robyn. Depends where you are (what Zone/how cold the winters) and how big the pots are to insulate the roots and also make room for them, as the clumps multiply underground. So like whiskey-barrel sized is going to give you more years than something small.