why and when to divide perennials, with ken druse (and tales of his latest flood)

I’VE BEEN SCOUTING around in my garden for orphaned plants, ones that used to be in visually pleasing clumps or masses, but because of expanding shade or a naughty vole or who knows what, aren’t looking as good as they used to. Over in New Jersey, Ken Druse has been digging and dividing some perennials, too, but for different reasons.

And that’s our topic: what and when and why and how to dig and divide.

Ken Druse is author of 20 garden books, and gardens on a small island in a river in New Jersey, which sometimes backfires as it did recently during Hurricane Ida, when the place flooded. He’s no longer underwater, so we talked about digging and dividing our way to a better garden.

Plus: Enter to win a signed copy of my book “A Way To Garden” by commenting in the box near the bottom of the page.

Read along as you listen to the Sept. 27, 2021 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on Apple Podcasts (iTunes) or Spotify or Stitcher (and browse my archive of podcasts here).

dividing perennials, with ken druse



Margaret Roach: Hi Ken, how are you doing? High and dry [laughter]?

Ken Druse: Dry.

Margaret: Is the ship afloat?

Ken: Drier. Well I love “a naughty vole.” A naughty vole.

Margaret: Yes.

Ken: Well, it’s not that hard to say. “A naughty vole.”

Margaret: A naughty vole. So the swamp report:  Maybe give us a couple of minutes of what happened.

Ken: Well, you may remember in the far-distant past, like four weeks ago, we had Hurricane Henri, and it didn’t flood. And I thought that we dodged a bullet. But the water was high, because I garden on an island in a river. And it has a fast branch on one side and a slow branch on the other. And the water did come up really high.

And there’s a wall on the fast branch, and it was about 6 inches below the top of the wall. And I thought, oh that’s great. And then 10 days later, on September 2, we had Hurricane Ida, and it did come over the wall. It was only about 4 inches more of water, but that was enough to burst everything.

Margaret: Right.

Ken: So the water came over the wall for about 24 hours, and the entire place was flooded. People always ask about the basement [laughter]. The house is one story higher than the garden, so I guess there was about an inch of water in the basement, and there’s the sump pump and that wasn’t really very bad.

But there was water on the entire garden. And in some places, the garden was the river. And I didn’t go out at 2:00 AM, but I’m sure that if I had, there were places where I would have been knocked over, because the water was deep.

Margaret: I was going to say is, it’s not just water, because when the water rises …

Ken: That’s where I was going, because usually we get sand and garbage and debris, and even rock, stones, right across the lawn. But this time it was… I call it debris, but it was mostly wood. And we had like six beer cans and some other things. There’s always a shoe sole, for some reason or another. But it was mostly wood mixed with sand. And we’ve had 2 feet of sand on beds in the past.

Margaret: Wow.

Ken: Distant past. But this time it was pieces, chunks of wood. And in some places it was a foot deep of chunks of wood, mostly small parts, but there was one tire, and some logs that were kind of bigger.

So we got to work, and the water receded in about 24 hours. And I took some video and some pictures. And then we started just picking up the wood and putting it in wheelbarrows and taking it across the river to where we have the compost piles. And we have a new, all-twig compost pile, which I guess we’ll mix with some other things.

But in the recent past, since Hurricane Irene about seven years ago, we’ve been planting to have more erosion control, and haven’t completely finished that yet. But there was one spot where an ash tree came down, and we planted some new plants this spring from Ed Bowen [at Issima Nursery] in Rhode Island, great unusual plants. And they were all gone. Nothing got washed away, because they… I mean, things got flattened and covered with this debris, but those new plants got washed away. And we found just about every single one stuck in the twigs and branches of flattened shrubs.

But I guess about three or four years ago, I had two Fargesia bamboos [below], which are the only non-running hardy bamboo, hardy to I guess Zone 5, maybe even colder.

Margaret: Right, you’ve talked about them on the show before. Right.

Ken: And so I started dividing them, which is not that easy, but they were young then. And planting them, because they’re very twiggy, right up against the wall that keeps the fast branch out. And I haven’t finished. And I did also some ostrich fern, but that Fargesia, really, it caught a lot of stuff and you can’t see it, which is great. But the soil didn’t wash away there, and usually the water runs right along the wall, so it’s working.

I’ve got to divide those plants—now they’re as big as the original plant. So I’ve got to dig them up and divide them, which I’ll probably do in the fall pretty soon. And plant more.

Margaret: O.K. So speaking of that then, of dividing: One of your motivations having experienced the flooding in the past, or just wet conditions in the past, however severe or not, was to do some, using some of the plants that are good for erosion control. Are there others do you use? Are there any other things?

Ken: No, I have tried the… Yes. I tried the ostrich fern, I tried yellow root. You know, Xanthorhiza.

Margaret: Xanthorhiza [simplicissima], yeah.

Ken: But it flooded very soon after I planted it. So I lost about half of those, and they take a while to get established, but I thought with that intricate root it would help. I’ve tried a lot of things, but the Fargesia is the winner so far.

Margaret: O.K. So my motivation for digging these last couple of weeks, and that I’ll be doing into the next few weeks, I have to say, it’s not force of nature. It’s force of neglect [laughter]. You know, where I haven’t had a lot of help last year and this year with the pandemic, the change in workforce and people’s realities where I live. There haven’t been a lot of people to help. And so certain things I turned a blind eye to. And it catches up with you.

So I’ve had groundcovers spilling out into the grass and kind of melting the grass, and making misshapen, too-big beds. And I’ve had in some cases, as I said in the intro to the show today, maybe a shrub or a tree has just gotten to that critical point of too big, casting too much shade on what used to be a gorgeous grouping of fill-in-the-blank. Sedum, primroses, you name it. Hostas, for goodness sake. And they’re in now too much shade, or maybe there’s too much rude competition from the nearby woody thing, and they’re not getting what they need, whatever the reason.

Or like you said before, naughty vole [laughter], or somebody digging, or who knows what. At the moment I’m in a fight against chipmunks, who are digging everything up.

But so there’s lots of reasons to be digging and dividing, and what I wanted to do both in the case of taking back the lines, the edges of the beds and getting all those flopped-over things back in place, cutting back those perennials that were trying to escape—and also finding ones that were orphaned, as I said before. The kind of onesies, where you used to have a nice patch of that Primula, and now you’ve got one here and one 3 feet away. It’s not a nice patch anymore [laughter]. And aggregating them, digging them up and finding a place for the new patch, and putting them together and trying to make more mass. So I don’t know if you’re doing any of that.

Ken: Well, I have in the past, but I’m kind of in recovery mode at the moment [laughter].

Margaret: Right.

Ken: But as you say that, that’s something while I’m recovering, I will be thinking about that. [Above, some small pieces of European ginger, Asarum europaeum, dug up and aggregated to eventually make a new mass.]

Margaret: Right. Because when I walked around—and I was really lucky, two friends who were professional gardeners came from the city, and I hired them and they came for the weekend and we had a lot of fun besides working. But we kind of went on a tour, that’s how we started. And we each brought a pad of paper, and we walked around.

And like you and I have talked about before, I call them treasure hunts. I try to accentuate the positive [laughter]. Like when I’m looking for weeds, I call it a treasure hunt because I might find some cool seedling of something, as you and I have discussed on previous shows, in the process of finding all the weeds. It was like a treasure hunt, finding those three primulas is that would look better together than they do three feet apart. And finding, ooh, I have this giant ‘Krossa Regal,’ two giant clumps of ‘Krossa Regal’ hosta way, way, way, way, way, way, way out there, where now it’s not an area of the garden anyone even looks at. And I’ve got like, $500 worth of ‘Krossa Regal.’ It would probably be even more than that, the way plant prices are right now. And I could make this whole beautiful show of that somewhere. And it feels cool shopping in your own garden, right?

Ken: You know, as you’re saying this, I’m also thinking of something that I call the third eye. And even if you can’t hire people, or you don’t have to hire people, just have guests come over with a pad and pencil and a third eye, because when you see stuff every day, you don’t see it very often [laughter].

Margaret: Right. Well, and that was the thing they were saying, my friends were saying, “What’s that?” And I was like, oh right, I’ve got six more of those, but one’s across the yard, and one’s up the hill, and one’s down by the road. Because it jogged my memory.

And what I did is—this is going to sound really nutty—but to store my cannas a couple of years ago, I have so many cannas that I store over the winter in the cellar, just bare-rooted, cleaned off. And I had bought a bunch of laundry baskets, big plastic, laundry baskets with the gripper handles. And so I got those out, and we put like-minded plants, similar plants—like we put all the hostas we found, we put in one basket, and all the whatevers, sedums that needed a sunnier spot that were now being shaded and splaying open and looking limp and stupid when they bloomed. We found them, and we’re going to find them a sunnier spot. We put them all in one basket. So I had these little stashes, and then we looked around for places to put them. And it was kind of fun. You have to make it fun, otherwise it’s just work, right?

Ken: And these plants weren’t dormant, so you must have taken pretty big clumps of soil with them.

Margaret: Yes, I did. And we ended up cutting back, the splayed-open sedums, we cut them back. But it has been moist. So that was the thing is, they’re going toward their dormancy anyway, so they’re not doing a whole lot of growth right now.

Ken: And believe it or not, it’s fall.

Margaret: Yeah, it is. And speaking of that, so isn’t that what we’re saying, is that this is a great time for this type of activity, right? Consolidation, repair, rejuvenation, divisions, dividing and relocating things. It’s a good time, right?

Ken: Yep, as things… Yeah, and it’s a good time to plant some stuff, too. Well, even to move shrubs. And you can move trees if they’re not that big, but that’s a whole other episode of the show. But the thing that we both discovered, but you taught me, is that it’s also a good time to sow grass seed. And I don’t know if you want to get into that, but…

Margaret: Yeah, well, like what I was saying, I had all this groundcover stuff, like Geranium macrorrhizum, one of my bulletproof groundcovers, like living mulch. But it eventually will flop out of the bed, and then your beautiful line becomes like “whoa, whoa,” like a scallop, you know what I mean? Where it flopped, you lose your line, and it wrecks the overall look of the garden. So what do you? You cut back…

Ken: Well, it gets shaggy. I wouldn’t say wrecks. It’s just that it’s untidy.

Margaret: Yeah. Well, if you see the pictures of a few places where I really let it go, it wrecks.

Ken: Well, I guess so. As you’re saying this, I’m thinking about what it’s like when you do it. You don’t think it’s that much, but in a way it’s kind of cheating, because you get such a big effect and you don’t even have to mow. It really is a big transformation.

Margaret: So I basically got rid of the outer part of that geranium that was overstepping…

Ken: Flopping over the…

Margaret: I cut an edge to the bed where I wanted the bed to be again, made a clear demarcation. [Below, the hacked-back geranium on the right, and the first blades of grass poking through 6 days after sowing.]

Ken: And the grass had been shaded out under the geranium?

Margaret: Oh, it was all melted. Yeah, it was dead. Yeah. And then I had to scratch that up and sow grass seed and so forth, yeah. But it came in so fast.

Ken: Well, I just spread some grass seed right on the surface, not even… Of some patches here before the flood, and then the flood came and I thought, well, that’s that. The grass seed is gone. A couple of days later…

Margaret: It’s not cheap, by the way, grass seed.

Ken: Right. And then after the flood, I saw little green hairs. So I guess the grass… I know the grass seed had actually sprouted, sent down its radical, its first little root. And this is in places that the water wasn’t running really fast, but it was underwater. And the water receded, and the grass grew. And it was, I think it was like five days. Four or five days.

Margaret: Right, me too. Same thing. I’m going to put some pictures of the day five, day 10 kind of thing, because it’s pretty amazing. And what it does, the improvement is so great. So…

Ken: Do you know why?

Margaret: Well, in the Northeast, August 15th to September 15th is the best period for growing grass in terms of the… We still have enough daylength, but it’s not too hot and too dry and so on and so forth.

Ken: Or too cold, or too hot. [Below, the newly sown grass less than three weeks after sowing.]

Margaret: Right, right. So peonies, what about those? A lot of people talk about peonies they want to move. What about you? You have any?

Ken: [Laughter.] I have some that I should move, because I don’t get to see them. And they’re too close to… Well, they’re in a place that I don’t even get to anymore, because there’s so many things in the way. That’s a good tip.

But they always say don’t move peonies because they live for at least… I mean, we don’t know how long they live, because I’ve seen ones that are over a hundred years old, and they’re still blooming and everything. But sometimes peonies don’t bloom, and that’s usually because they’ve been planted too deep or too shallow. I’d say generally too deep, and we can talk about that.

But sometimes you want to move them because you have a whole lot, and you’d like to have them in more than one place. Or sometimes they’re in the way of something, or they’ve gotten into too much shade, like you talked about before. Or you might want to… I think this would be a good place for a patio, but my hundred-year-old peonies are there.

And one reason they say not to move them is because it takes a little bit of time, sometimes a year or two to recover. And because you don’t have to move them, they don’t like to be disturbed.

But if you’ve planted peonies deeper than 2 inches, they may not bloom. In cold climates we plant them about 2 inches deep, and in hot climates we plant them about 1 inch deep. So that’s the crown, the top of this big woody clump. You want that to be between 1 and 2 inches deep. And you can also often in this time of year, which is the right time to do it as they’re going dormant, we’re already cutting off their brown or black foliage. And if it’s spotted we put it in the trash, and if it’s just turned brown we can compost it. But you’ll see these little pink… I call them eyes.

Margaret: Eyes, right.

Ken: They’re buds for next year’s growth. And we don’t want to damage them, of course. But when we cut apart the peonies with a chainsaw—I’m kidding—but with something, a saw, something sharp, because it’s very woody. You want to have at the very least one eye, but usually three or four eyes on each piece of the clump.

Margaret: Right, the divisions need to have eyes, so like potatoes. I mean, not like potatoes in terms of texture or aggregation of the size of the clumps, but I’m just saying, something like that needs eyes in order to sprout.

Ken: Right. And with peonies they’re on the top there. They’re really easy to see, and this time of year they’re probably three-quarters of an inch high and pointed, and often kind of pink. But it’s interesting because they say never move a peony, but sometimes you have to.

Margaret: Right. And so mine, I have all these wonderful peonies in some of my favorite colors, a lot of coral ones and so forth. Well, where are they? They’re in an area, and this was on my little tour with my friends a couple of weeks ago with our notepads in hand. I have this big area, and a tree and a shrub near to them are now casting long shadows on them. And so they are not performing well. They’re totally alive, but they’re not making profuse blooms. And so I have this wonderful stash of great named peony varieties in beautiful colors that I’m, like you said, no longer getting to enjoy.

Now that would have been a whole day or two project for us, because it’s a lot of digging. And finding a new home for them that was sunny, because if I’m going to do the work, I want to put it somewhere where it’s going to have longevity in its new home, not a stop-gap situation. And as you said, they’re not going to be in peak performance again for another year or two. So I want to make sure it’s the right spot.

So I didn’t do that. But what do you think? I mean, we were talking that day after we didn’t get to those, and saying, you know what, maybe we’ll break the rules and do them in the spring. I mean, what do you think about that?

Ken: You can do it. It’s funny because peonies are almost always sold for planting in the fall when they’re dormant. I don’t know if that’s just convention or some kind of horticultural voodoo wisdom. I’m not exactly sure, but it’s probably that they get established better in the fall when the ground is still a little warm, and they can make some new roots and they are dormant. When we buy them in the spring, they’re usually potted. [Above, ‘Coral Charm’ peony at Ken’s.]

Margaret: Sure. Of course, there are up and growing already, so you’re not disturbing them.

Ken: So it’s a different kind of thing. I’m sure that you could do it without a problem. It’s possible that they maybe take longer to establish.

Margaret: That’s what I think.

Ken: And instead of blooming in two years, they might bloom in four years, and that would be kind of a drag. But I wonder [laughter] why don’t you cut down those trees? They must be special trees.

Margaret: Yeah, they’re special. And I think that’s what it is, is I’m not going to kill them by digging them at the wrong time, I don’t think. I think I’m going to delay their bouncing back.

I want to ask this before we run out of time, I want to ask you, other reasons. So we talked about reasons for dividing. So you’re making more of some things that are helping you to make, what were you calling it? What are you using the Fargesia for? Oh, erosion control.

Ken: Erosion control.

Margaret: I was about to say flood control, but that’s not what I meant [laughter]. And I was talking about getting rid of orphaned onesies. That’s another reason, aggregating for more visual impact.

And then I was also saying another reason for dividing or moving clumps of perennials right now is to take back the shape of beds if things have spilled over too much, gotten too big.

But then there’s another reason, some things get really weak in the center, like there’s a doughnut of dead material in the center of Siberian irises and stuff. Do you have any of that ever going on?

Ken: Of course. With Siberian iris, that’s a perfect example. And then you do need a chainsaw for that. But as you’re saying this, I said, “Cut down the tree.” I don’t cut down trees.

Margaret: I know that.

Ken: Sometimes I think, oh, I should cut that tree down. But I planted it, blah-blah-blah. But as you’re talking, I’m thinking really another reason to do it is to share. If I have too much of a plant, and it’s not invasive or anything, I’ll divide it or propagate it. I can’t throw the pieces away, I’ve got to root them. And I’ve got to take that chunk in the division and share it with somebody.

And another reason is because maybe something is doing really well, and you think wouldn’t that be nice to have—just the erosion control—but to have an edge of that plant, to have more of it in a certain place. I mean, there’s lots of reasons to divide plants. And as you said, for the health of the plant, with that iris it’s just going to stop blooming and have a big donut dead center. But if you divide it, it will rejuvenate and grow and become a clump again. Division is a good thing.

Margaret: Yeah. And again, going on a scouting trip right now around your garden, however big or small or young or old it is, with that pad of paper, I guarantee you’re going to find some cool things. Like I found I had a lot of purple-leaved heucheras, but they were here and there and everywhere. And in our solution to one area where the sedums weren’t getting enough light and were splaying open at bloom time, we needed something that could be a little more shade-tolerant, and was going to look nice a lot. And there happened to be other purple things in that area. And it was like, boom.

And I just was so excited that I had the plants. Do you know what I mean? It felt like such a victory. It wasn’t like, all is lost. Oh, look, these are no good anymore. It was like, wow, a second life. So there’s the good feeling to it, too.

But anyway, so yeah. So you’re all cleaned up as we say?

Ken: Well, mostly [laughter].

Margaret: Good, good. All right. Well, it’s always good to talk to you.

Ken: O.K. Divide and conquer.

enter to win a signed copy of ‘a way to garden’

I’LL SEND A signed copy of my book “A Way to Garden” to one lucky reader. All you have to do to enter the giveaway is answer this question in the comments box farther down the page:

What at your place is in need of some division and why?

No answer or feeling shy? Just say something like “count me in” and I will, ,but a reply is even better. I’ll pick a random winner after entries close at midnight Tuesday, October 5, 2021. Good luck to all.

prefer the podcast version of the show?

MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 11th year in March 2020. 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 Sept. 27, 2021 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).

  1. Debra says:

    I have lots of plants to divide and share – peonies, indigo – mostly because they have done so well, and are huge, overcrowding themselves and other plants.

  2. Susan Vogt says:

    I have an overgrown rhubarb patch that I will dig up and divide soon. I’m happy to do this because we’re moving back to our hometown in western Maine (from Central Maine). Our new property has no rhubarb and we must have rhubarb for delicious strawberry rhubarb pie.

    1. Judi Heiser says:

      My Hosta’s need dividing. I’ve been dividing them over the past few years and have managed to create border/beds across my back yard from just one plant!

  3. Alan says:

    The purple bearded iris out back has been untouched for at least 8 years (we rent, it could be much longer) and I’ve been meaning to divide for a couple of years since learning it needed doing. This year was so busy I didn’t get to do it last month, but maybe next year.

  4. Maureen Brown says:

    My yellow-flowering baptisia needs dividing after slowly taking up more space over perhaps 15 years. Also my largest hosta, and forgive me, I no longer have the exact name handy. My Japanese painted fern could use dividing if it’s safe to do so, as well. That, or let it take over the plot and have a “fern crescent” arcing out from garage toward back door of house.

  5. Katherine says:

    I want a GOOD book to curl up with when the weather starts biting with colder temps, the wind joins in with rain, sleet and snow adding to the mix. I’d love to read this book and time travel back remembering all the good times in the garden in spring, summer and fall. This book would be my go to to escape the winter blahs and blues!

  6. Robin Muszynski says:

    I just wanted to say on the subject of erosion control, that I’ve had great luck using Sorbaria sorbifolia, what I call False Spirea.

  7. margaret says:

    AND THE WINNER IS: Wendy. Thank you for your answers (we feel better knowing it’s not just us who have some dividing work ahead of us).

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