I’VE NEVER HAD a rock garden, I confess, but a new book about a modern and extreme form of the art caught my attention recently. It’s called “The Crevice Garden: How to Make the Perfect Home for Plants from Rocky Places.” And its authors joined me in a conversation about why you might want to make room for one, and the plants it can support.
Colorado-based Kenton Seth and Paul Spriggs from British Columbia are garden designers with a particular specialty in rock gardens. We did a “New York Times” garden column together not long ago, and I wanted to learn more.
When they appeared this spring on the popular Garden Masterclass webinar series, British host Noel Kingsbury said this in the way of introducing them: “Rock gardening will no longer elicit a yawn because this is the future.”
I was so glad to talk with them to give us a peek into this brave new world. (Above, from the book, part of a crevice garden at Denver Botanic Gardens.)
Plus: Enter to win a copy of the new book by commenting in the box near the bottom of the page.
Read along as you listen to the Aug. 22, 2022 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).
Plus: Enter to win a copy of the book by commenting in the box near the bottom of the page.
crevice gardens, with paul spriggs and kenton seth
Margaret Roach: Thanks for getting up early in the morning, because I know you’re hours earlier than we are. To start, and I don’t know who wants to answer which question so you can alternate or whatever: What’s the elevator pitch of what a crevice garden is, say, compared to a more conventional rock garden. What’s a crevice garden?
Paul Spriggs: Kenton, you want to take that one?
Kenton Seth [above]: Yeah. The true elevator speech to the layperson who’s not a gardener, I like to say it’s like a bonsai-ed mountain to grow plants from rocky places, usually little rock plants. Miniaturized mountain ranges in people’s backyards, I think is an easy way to describe it, or at least that’s how I would see it if I came from the total outside.
Paul: And then of course, it’s also an improved style in terms of its ability to grow these difficult-to-grow plants. As far as my elevator pitch would go for someone getting into rock gardening, they might find that a garden constructed strictly out of crevices is the best way to succeed in having that type of a plant collection.
Margaret: O.K. So when you say just crevices, I’m taking that there’s more rock than in your average rock garden, and the planting spaces are tighter in a crevice garden, as in they are crevices only.
Paul: Exactly. A traditional rock garden is, for all intents and purposes, a mound of soil just covered up with rocks and gravel, and it certainly serves the purpose for lots of plants. But a crevice garden, the rocks are all buried very deeply to create that deep crevice condition that a lot of these plants from rocky places really prefer.
Margaret: You had an allusion in the Times story, and when we had done the interview for that, you guys talked about sedimentary rock, or rocks that are stratified, and the image of a like a dish drainer with plates in it. Do you know what I mean? You’re talking about how they’re buried. So tell me about that.
Kenton: That’s a good way to describe, I guess you’d say mainstream, or traditional, or the nascent form of crevice gardening where linear, slab-like stones were stood on end. And that idea was inspired from natural places that look like that. But crevice gardens have gone beyond that, too. They’re not just vertical stones anymore. There’s horizontal and diagonal and round stones and blocky stones. Most classic crevice gardens are recognizable with that sort of traditional style.
Margaret: O.K. A lot of people asked this in the comments on the Times story: Are these only for places like Colorado or mountainous, rocky, harsh?
Kenton: Oh, no.
Margaret: Are these for anywhere?
Kenton: Ironically, they were developed in more mild places, to grow plants from the harsh places. So they started in nicer climates really, to be honest. They’re used in Europe, in lowland parts of Europe in the cities there to grow plants from the mountains. It just turns out that physics is the same everywhere, and what makes the crevice work there makes it work where I’m at in the real dry, arid West as well. So they’re quite universal.
Margaret: So Paul, where in a home landscape can we fit one? I know many botanical gardens have them and are using them for various purposes, including preservation and conservation of imperiled species and so forth. But where in a home landscape can I put a crevice garden? How much room do I have to have and so forth?
Paul [above]: Well, you can have as big or as small as you want. And like any garden feature, it has to fit into your overall landscape so that it doesn’t stand out like a sore thumb. Obviously, if you’re just a plant collector, and you don’t care about how your garden really looks, well, then that’s not as much of an issue. But for me, it needs to fit into the garden, and the crevice garden can fit into all types of places.
If it’s a small garden, it can be tucked up near a garage door or a front entranceway to the house, along the side of a pathway or a driveway. Or it could be its own free-standing feature out in the middle of a large expansive lawn or in a large gravel meadow. There’s really all kinds of places it can go, as long as it doesn’t feel squished in there and as long as it isn’t up against a lot of trees, it really wants to stand on its own, so to speak. A lot of these gardens like the brightest, fullest type of conditions you can get. So it really fits in in all kinds of places as a focal point and a great way to grow plants.
Margaret: And you guys kind of alluded to this a little bit, so the rocks, whichever shape, are buried partly in the ground, but they’re not buried in a flat canvas of soil. This is mounded, like a berm, this is not something that’s flat to the ground, right? [Below, soil is mounded up before rocks are partially buried, to make a crevice garden.]
Paul: Definitely not.
Kenton: No, not usually. You could, but then it’d be a patio [laughter].
Margaret: “How to build a patio” with Kenton and Paul.
Paul: We’re trying to build dramatic, natural-looking for the most part, features. And the mountains are our inspiration for that. And so essentially, I think of it as like a miniature mountain, I try to build something that looks like it might be hard to climb.
Kenton: And for folks in wet climates, building it up that increases the drainage. The surface drainage will dry out the garden for those plants and is really helpful.
Paul: And it also gives the depth that those plants need. A lot of them are tap rooted quite deeply. So the crevice garden will give them that depth that they need.
Margaret: So they get a deep root run in these tight spaces. And in there is not our conventional soil that we’ve all been taught as gardeners [laughter] to try to create highly organic humus, whatever, these are plants from lean, mean spots, yes? That we’re going to be growing? And we’ll talk more about which plants in a minute.
Kenton: Yeah, they like junk [laughter]. Some of them are growing in pure gravel in the mountains. Paul and I, when we did research for the book and traveled around and met people, most places, people used pure sand, builders sand, as the growing media.
But then in places that are a little drier in climate, like me or even Central Europe, I started using more rock dusts, gravel fines, if you want to call it that. And some of them would use tiny, tiny bits of compost if they’re growing certain plants, but not usually. It was usually minerals and it was usually rock dust.
Margaret: So not an organic soil, not a lot of compost and humus and all that.
Kenton: Compost is an exception when it shows up in crevice gardens.
Paul: Yeah. All that nutrients will cause the plants to grow out of character, if not outright kill them.
Margaret: Which is why some of the plants that are grown in crevice gardens, we may have killed them in a year or two or three or even more quickly in our conventional garden beds, right? These alpine plants especially, they’re not going to tolerate our traditional garden beds.
Paul: Well, killing plants is part of gardening in my experience.
Margaret: [Laughter.] It’s never happened to me. I’ve never. No.
Paul: No, of course not.
Paul: Every time you kill a plant, you learn.
Kenton: It’s the only way to know the limits.
Paul: That’s right, exactly.
Margaret: Yeah. So just so that we could visualize if we were getting started, what would be some of the things that I might put in my initial crevice garden? If I made this berm, this outcrop kind of a garden, with these partly buried stones and a fast-draining medium, what would be some of the candidates?
And I know that it can be very rare, treasured things that you all get from seed exchanges from the North American Rock Garden Society members and all kinds of wishlist plants, but for beginners, not that advanced stuff.
Paul: I would say if you’re a beginner, there’s a whole suite of what I call garden-center alpines, that you walk into the garden center and they’re all in their little 4-inch pots, like Armeria maritima, and the creeping thymes, and those types of things. If you want that instant mountain look, those are good starters. Sempervivum, like hens and chicks are an excellent candidate for a beginner crevice gardener.
But people often, as they move through that journey, then they slowly want to grow more challenging, more difficult and things that may not be easily available. So there’s a whole gamut of things. But for beginners, I would say Sempervivum is probably the best plant for the crevice garden.
Kenton: Yeah. I still love them.
Paul: No shame.
Margaret: They are amazing. Little living sculptures, right?
Paul: Yeah. And they fit the bill so perfectly in that they’re somewhat disposable and they’re so easy to propagate that if you need a spot for them, you just plunk them in anywhere just to fill the space. And then if you need a place for a better plant, out they come and then no love lost.
Margaret: What about some of the hardy ice plants? They’re sort of succulent-y, right?
Kenton: Yeah. A lot of them that are commercially available can be fast growing carpets, but there’s some new hybrids now that stay a little more compact and there’s some species that stay smaller that’d be more appropriate for the crevice garden. Like Delosperma congestum, yeah, those guys love a crevice garden. They do great in there.
Margaret: And some of the little garden pinks, I love some of the little bun-shaped flowering things. Do you know what I mean? The little Dianthus, the little Campanula. Because it’s so preposterous that there’s this thing in this pocket of rock, and then suddenly it sends up these flowers.
Kenton: There seems to be a rock garden or miniature version or species of most garden perennials. There’s miniature verbascums, even, or miniature Digitalis. You nailed it though, pinks and bluebells are classic and awesome.
Margaret: So the Dianthus and the Campanula, is that what they’re called?
Paul: Oh, yeah. They’re classics. There’s so many species. And rock gardeners have been growing them for a hundred years [laughter].
Margaret: And you guys grow woody plants in these gardens too, don’t you? That’s what blows my mind. It’s like, how in the world did you get those to grow in there?
Paul: Well, for me personally, it’s all about the dwarf shrubs. If I was to choose two that were really the ones that I like the best it would be any selection of dwarf conifers, and Daphne is also one of my favorite genera as well. And they’re all very well suited to the crevice garden, provided they’re in scale with the garden. You don’t want them to overgrow, but as long as they stay small, they’re perfect. And the woodies are great, because you do see those in nature in these extreme environments often represented as a krummholz, which is a windswept, wind-pruned tree way up on the mountain crest.
Margaret: And what’s that word?
Paul: Krummholz. It’s a German word. It means crooked wood [laughter].
Margaret: Oh, O.K.
Kenton: You know those trees you see up at treeline that are blown sideways? All the leaves or needles are only on one side. They’re kind of naturally bonsai-ed.
Paul: And a tree that in the valley bottom would be 150 feet tall is 2 feet tall up there [laughter], and maybe the same age.
Kenton: You can bring that spirit of the mountains down to your garden.
Paul: Yeah. That’s the whole idea. One of them.
Margaret: So like dwarf Alberta spruces?
Margaret: And what else? Some examples.
Paul: Well, all the conifers, pines, spruces, cedars, Cryptomeria, they all have dwarf versions. Often they’re witches’ brooms that have been discovered in nature, and then people can graft and take cuttings of those original dwarf witches’ brooms, and they retain their character in the garden.
Margaret: Just tell everybody what a witches’ broom is.
Paul: It’s a parasitic growth on a host tree, which basically creates a growth that’s mutant, but often highly desirable, because they’re essentially dwarf versions and often bun-forming or pendulous versions of the mother tree. But when you take a cutting or graft off of those, they retain the character. And so then you’ve got yourself a dwarf conifer [laughter].
Kenton: It’s cool how wonderfully available those are in the states right now. I see them at a lot of garden centers. And maybe they were producing to ramp up for the fairy gardening movement or the bonsai gardener. So those are nicely available.
Margaret: So I’m not getting out my big, long-handled shovel. And I’m not starting with a 5-gallon pot of some woody plant, or for that matter, even with the Dianthus or the Campanula, or the hands and chicks or whatever. I’m not starting with probably even a court pot, let alone a gallon. This is small. We’re going to tuck small things in with small tools and small plants. How does that work?
Kenton: Well, and it also reminds me to point out that the smallest crevice gardens can be in a pot themselves. So everything can be even tinier than tiny. But as you were pointing out, all the work in a crevice garden and the maintenance is just miniaturized. Instead of wheelbarrows of cuttings, you have a handful of cuttings. And rarely do we ever plant plants that are in a pot larger than a 2-inch pot. [Above, from the book, container crevice gardens by designer Chris Dixon.]
Paul: And when you think about these crevices, they’re only 1 inch wide as a rule. So like you say, you can’t put a 1-gallon pot in there. Well, you can if you bare-root it and you really modify the roots. But typically, everything’s done in either 2-inch pots or even straight as seedlings that have been germinated in a separate pot or as rooted cuttings. Those are all different ways. And certainly those last two ways are great because you’re talking about such a small root area that may only go down 4 or 5 inches and basically doesn’t really expand sideways at all. So planting seedlings and cuttings is a great way to get the garden going, although you do have to baby them once they’re in for a bit.
Margaret: I was going to say, these are water-wise, so to speak, low-water-usage gardens because they’re mimicking these places in nature where it’s harsh and so forth. And the medium is fast-draining and so it’s not absorbing and holding a lot of water. But in the beginning, what do I have to do? So I’ve got these practically bare-rooted things, these young things, I’ve tucked them into these 1-inch gaps, these spaces of planting medium between these rocks. What do I have to do to get them acclimated? Do I have to water initially for a while?
Kenton: You sure do. All plants, no matter how tough they are, are tender when they’re babies, even if they’re cactus or whatnot. So they do require a bit of babying up front. But we find they establish pretty quickly in a rock garden situation, especially if they’re bare-rooted and put in without their potting mix, they establish pretty nicely. And you can usually tell. My rule of thumb is if the plant got bigger, it’s more established.
Paul: Yeah. Because a lot of these rock garden plants, even when you grow them from seeds, two months after germination, you’ll have a plant that’s just half an inch high, but then the root is 8 inches long already. So the point is that they fire the roots down, and I believe the crevice encourages that deeper rooting and quick rooting, which basically makes them less prone to desiccation when conditions get tough.
Margaret: O.K. So you’ve worked on, you just mentioned it can be as small as a container garden. And obviously we wouldn’t use the most fragile, delicate container. It’d probably be a trough, or I love the idea of a galvanized tub, almost like a horse trough kind of a thing with rocks.
Kenton: We’ve seen some beautiful ones lately of the horse troughs, or painted copper and whatnot, they’re just gorgeous. It just further elevates this little mountain. Yeah, very cool.
Margaret: Yeah. And it brings it up, because of these little treasures, it brings it up closer to eye view, so that we can really look at them, we don’t have to crawl around to look at them. It’s kind of fun.
Margaret: Yeah. And we’ve talked about rock, rock rock. One of the gardens that you turned me on to, that I think you may have consulted on, or did consult on, that used recycled concrete from an old foundation and I think an old parking space. In other words, they didn’t bring in rock. It can be expensive, and some places it’s not widely available and so forth. This was at Plant Delights Nursery, or their Juniper Level Botanic Garden in Raleigh, North Carolina. And they used all this recycled chunks of concrete and they made, I think, what is it, 300 feet long or something, this thing [laughter]? [Above, part of the Juniper Level crevice garden.]
Kenton: I can’t even keep track. We’re pretty sure that’s the largest crevice garden on earth now. Yeah. And actually, that wasn’t really even the first big broken concrete installation. The Dutch should get credit for it, the University of Utrecht, because they don’t have rocks in Holland, they built these broken sidewalk concrete spheres out of broken concrete, with these beautiful spheres of plants growing out of them. They did that a while ago.
So that’s a thing, for sure, just to illustrate your point that where rocks are not available or are too expensive, broken concrete’s everywhere there are humans. What I love about that is it levels the playing field. So even if you don’t have a huge budget or you’re not in a region where rocks are easy to get, broken concrete’s great. And you can see it as an ecological thing, too, since concrete is known to be such a big resource-intensive material that we create.
Margaret: Right, to upcycle it like this and utilize it.
Kenton: Exactly. Some rock garden friends have jokingly called it “anthropocene limestone,” because it functions the same way.
Paul: We also call it “urbanite.”
Margaret: Urbanite, right.
Paul: It can look very natural. The broken ends of a piece of concrete can basically look like a rock when it’s all put together properly.
Kenton: You can go both ways with it.
Paul: Yeah. You can fool people [laughter].
Kenton: It’s amazing.
Margaret: So I want to just talk a little bit about if people want to learn more and they want to get involved, I was really impressed that you’ve started this community, I don’t know how many years ago you started this Facebook community [Modern Crevice Gardens], and there’s a lot of people in that. And plus, that, and also the resources of getting to know the North American Rock Garden Society, which has 30-something chapters around the country and great websites and all kinds of learning information. Tell us a little bit about if people want to become part of this community, either virtually or in person.
Kenton: There are, like you point out, mountains of information and nice people out there for this, which is surprising for what seems like such an esoteric gardening style [laughter]. But you mentioned the Facebook page that Paul and I started called Modern Crevice Gardens.
There’s a rock-garden club in most English-speaking countries, or all of them, and there might be local chapters. It’s worth hunting them down. You mentioned NARGS, North American Rock Garden Society. And there’s one in England and Scotland and there’s a French and a German and Czech version, too. Yeah, there’s a lot of friendly people out there to teach you or just hook you up with the right books.
Paul: And I feel that it’s actually important if you really want to get into stuff to join one of those clubs, because this is not mainstream gardening. This is not the kind of thing where you walk into a garden center and you’re going to see a crevice garden. Maybe one day you will.
But a lot of the plants are just straight up not available. And so you really need to know people to be able to make those connections, because there’s a lot of exchanging of plants, exchanging of seeds, all that type of thing. And if you’re just an island unto yourself out there and not connected with the community, you just may find it harder to make the progress that you want to make in this world.
Kenton: The learning’s such an ongoing journey, too. It’s nice to seek that mentorship. I think that’s why we love it so much, is that you’re never done learning about it. There’s always a new group of plants.
Margaret: Just a final thought, and it relates to the Plant Delights concrete upcycled crevice garden galore [laughter], is that it can be a retaining wall, which that sort of does serve as. Instead of building a concrete or brick wall, you can make it permeable, so to speak, and planting it and make it a live thing. Which I love that.
Kenton: I think that might be one of the freshest things about it is looking at a crevice garden as habitat. Because I think a lot of Americans are thinking of their gardens now as potential habitat for pollinators, birds, etc. And some folks have known for a long time that crevice gardens attract the lizards and the butterflies to warm their wings and the spiders that eat their pests.
Paul: And that the ground-burrowing bees.
Margaret: Yes, yes.
Kenton: Oh yeah. That’s where they go in my garden for sure. They go to the crevice garden.
Margaret: [Laughter.] Well, Kenton Seth and Paul Spriggs, the authors of the new book, “The Crevice Garden: How to Make the Perfect Home for Plants from Rocky Places” [affiliate link], which we’re going to have a giveaway of. I’m so glad we did the piece for the Times because I feel like this is something that people need to know about. And I think it has a role in a lot of different places, as you’ve been saying. So thank you. Thanks for making time today.
Paul: Thanks for having us.
Kenton: Thank you so much. It’s been a treat.
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