Now Ruth Rogers Clausen, one author of that well-used 1989 book, has teamed with another longtime horticulturist and garden writer, Tom Christopher, to create a volume that better matches the palette of plants packing the benches of today’s nurseries—and also better serves gardeners in the hot, humid Southeast, not just cooler and drier regions, something the earlier book didn’t. (I’m sharing a copy in the latest giveaway; enter at the bottom of the page.)
Their new book is “Essential Perennials: The Complete Reference to 2700 Perennials for the Home Garden,” and it is a collaboration with a special backstory: Ruth, a British-trained horticulturist, was Tom’s first horticulture teacher, when he studied at the New York Botanical Garden.
Read along as you listen to the Feb. 23, 2015 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).
listen/read: perennial q&a with tom christopher
Q. If it’s even possible, Tom, we should probably try to characterize what has happened to the perennial category of plants in the marketplace since the previous book. I think in the introduction to “Essential Perennials,” it says it’s gone from “famine to feast.”
A. The big challenge 25 or 30 years ago was to find good perennials; there just weren’t many sources in the United States. Now it’s kind of the opposite. There’s a tsunami of great material, but how does the average gardener figure out what will serve them best?
Q. I think in the introduction it also says there are “tens of thousands of new cultivars and species” introduced the last 30 years to the U.S. market to sort through.
A. There are tens of thousands when you just consider hostas and daylilies.
Q. Do you remember the palette of your first perennial garden that you planted?
A. I was right out of the horticultural training program at NYBG, and was working on an old Hudson River estate. There was a long-neglected but very beautiful walled garden—it had been neglected for decades.
So I got to experience perennials that are “unkillable”—forget-me-nots (Myosotis), hostas, Virginia bluebells, bearded iris, peonies.
A. Peonies, for instance, will just keep coming back. I’ve seen ones that I’ve been told confidently were 60 or 70 years old.
Q. I call some of those my “confidence-building plants,” the ones that you cannot kill. Bee balm, for instance, is another.
A. That’s a good expression–and I still like them.
Q. I remember not long after I bought my place, the use of Rudbeckia, and Sedum ‘Autumn Joy’ [above] and the start of the ornamental grasses trend was happening. Perovskia, Nepeta (the catmints)—those were plants that seemed “new” at the time, and everyone was using them. I’m afraid other than the Sedum I’ve gotten rid of all the rest out of exhaustion at looking at them. [Laughter.]
A. We do like to keep trying new things.
Q. I expect you two began with the “old” book’s index, and tried to subtract/add to the plant list there as a first step in making the “new” book? Tell us a little about how you even begin to tackle such a massive project, with no right or wrong table of contents, but instead a lot of judgment required.
A. Ruth is a fanatical plantsperson, so she took the lead. But we did discuss what we would leave out—most of the grasses, ferns and bulbs, for instance, that would go in a perennial garden but didn’t meet our criteria. The book just would have become unmanageably large.
We included some Southeastern plants, which hadn’t been in the original guide—like Colocasia, the elephant ears, for instance. I gardened for four years in Central Texas, where I got a lot of experience with summer hardiness.
Q. Plants that someone like me up North thinks are “annuals.”
Was one of the exercises also a taxonomic one—updating the old names to new ones? So many plants have changed names in the last 25 or 30 years.
A. I’ve got a secret for you: There is a resource online called The Plantlist, which is maintained by Kew, the Missouri Botanical Garden and the New York Botanical Garden. It’s a fabulous resource for anyone looking for what the latest taxonomic name of a plant is.
Some of the Corydalis have changed [the former C. lutea [above] and C. ochroleuca are now classified in the genus Pseudofumaria]; the asters have pretty much all changed. Some have been changed and then changed back—like the chrysanthemums.
Sometimes I think the botanists just want to keep us all running around from book to book, hanging on their latest word.
Q. Speaking of New York Botanical Garden, and botanists, and taxonomic name changes, a year ago I spoke to the ethnobotanist Michael Balick from there, and he said they’re not really trying to drive us all mad. He says the name changing has an application in the name of science—for instance when it was discovered that some yews, or Taxus, contained the cancer-fighting substance taxol, that there wasn’t enough of that species to make enough of the drug.
So they evaluated the chromosomes of related species to see which ones were closest, as an alternate source. In the ethnobotanical world—botanists studying the uses of plants—it allows them to figure out the closest cousins.
So it wasn’t just to drive me crazy. [Laughter.]
What’s especially important to readers seeking perennial advice—that perhaps you hoped to provide in each species entry?
A. The obvious cultural things, such as light adaptation and soil requirements, of course, had to be included. But we also wanted to make sure to include habitat and native range—which are increasingly important in preventing invasive plants from entering this country. But also if you tell somebody something is a grassland plant, it gives them a clue of what conditions to give it in their garden.
Q. Don’t grow it in a swamp or the dark!
A. Right. And we looked for deer and pest resistance. We also included notes on tolerance to a combination of heat and humidity—the great killer of plants in the Southeast. When I gardeners in Texas, we’d say they “melted.” So often in the older book they’d list something as hardy to Zone 8, but they’d mean Zone 8 on the West Coast, where it’s dry–a big difference with things like lavenders, for example.
Q. How did you even reckon with some of the big genera of plants? Like the daylilies?
A. There was no point in focusing on individual cultivars too much, so we focused on different classes and types of flowers—including tips that would help you figure out if it would do well for you. For instance, the evergreen daylilies are better for warm climates; the ones that go dormant in winter for cold climates.
Then there are the tetraploids versus the diploids. The tetraploids, having twice as many chromosomes, tend to make bigger, huskier plants with more intense colors. [Top-of-page photo, tetraploid ‘Chicago Apache.’]
Q. I didn’t know they had more vivid colors than the diploids.
A. There again: The fragrant hostas are better for Southern gardens, because they all descended from the most humidity-tolerant one, Hosta plantaginea. We also talked about things like how the gold hostas [above, emerging in spring] are better for sunnier spots, or they don’t color up…
Q. …and by that you don’t mean baking out in the middle of the yard all day.
A. No, but they’re tolerant of some afternoon sun, where a lot of hostas will burn.
Q. What about the peonies? I always thought they don’t do in the South, but that’s not true.
A. The single-flowered ones are better in the South, and you also want to go for other early blooming types that get through flowering before it gets really hot. [The intersectional peonies, a cross between herbaceous and tree peonies, cope well with hot, humid Southeast summers, too, says “Essential Perennials.”]
Another useful hint: Double-flowered types tend to be more fragrant.
Q. With plants that are tricky to grow or known for having an issue with pests or disease, who did you turn to for reliable advice—since you couldn’t trial them all, all over the nation? Like with Phlox and their mildew issues, or Monarda?
A. Ruth has written a book about deer-resistant plants, so that was helpful. Also, the Chicago Botanic Garden has done a lot of plant-evaluation trials, so that was very helpful. We tried to look for systematic trials like those to refer to—it’s one thing for someone to say they noticed something didn’t get mildew in their own garden; it’s another thing to have it tested, such as all the phlox trialed together.
Within a genus like Phlox, we tried to steer people to the species that are more disease and problem-free. You don’t have to just grow summer phlox, P. paniculata. You could grow others, like P. glaberrima, the spring-blooming smooth phlox, that can fulfill some of the same requirements in the garden but with less problems with deer and mildew. In the book we list a rose-pink one called ‘Morris Berd,’ and one with pink-lavender flowers and white-edged leaves, called ‘Triple Play.’
Q. What genera were especially hard to untangle for other reasons—not necessarily numbers of varieties like the daylilies, but challenging for another reason?
A. Some genera were real headaches to sort out—especially the one that have become collector’s plants, like with Sedum, or Echeveria. Tiny little differences between these plants will be important to the collector—but the average person isn’t going to notice. There we looked more for availability—what people would see in their catalogs and local garden centers—and tried to rate the best of those. I still like ‘Autumn Joy’ [and its flashy cousin, ‘Neon,’ above, is also recommended in “Essential Perennials.”]
Q. With Salvia, for example—I have seen many of them again and again, but can’t really tell them apart for the most part.
A. There are hundreds of species of Salvia, so there we tried to focus on the most useful and broadly adapted species—unless there was something so wonderful we couldn’t bear to leave it out (because personal preference did some into this at a certain point). But generally we chose plants we thought people would find most useful.
Q. Do you grow any perennial Salvia? I guess I only use tender ones, as annuals, to attract hummingbirds—but no perennial ones, come to think of it.
A. I did in Texas, and now I grow some in my Connecticut herb garden—but tender ones, like pineapple sage.
A. I think that I’d rather not cope with the Echeveria again—they’re the supreme collector’s plant, and trying to untangle all of that was such a headache. [Laughter.]
They’re useful, and beautiful in containers [above], and I’m glad they’re in the book—but not in my garden.
With Echinacea, the purple coneflower, it was a revelation to me looking at all the new cultivars out there in great colors: whites, reds, yellows, even green-flowered ones.
I love the green ones—like ‘Green Jade’ and ‘Green Envy’—and they’re all great in cut arrangements.
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 seventh year in March 2016. 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 Feb. 23, 2015 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).
enter to win ‘essential perennials’
I’VE BOUGHT TWO extra copies of “Essential Perennials: The Complete Reference to 2700 Perennials for the Home Garden,” to share with readers. To enter, answer this question in the comments box below the very last comment on the page:
What perennial have you had enough of, and which one is on your wishlist right now (or something you already give a front-and-center spot in your garden to)?
For Tom it was no to Echeveria but yes to the new coneflower colors. I confess I need to go on a rampage against some too-enthusiastic groundcovers I planted early on in my garden, including Lamiastrum, and these days am drawn to new perennials with colorful or variegated foliage most of all.
No answer, or feeling shy? Just say, “Count me in” or something like that, and I will. But a reply is even better. I’ll draw two random winners and email them after entries close at midnight on Saturday, February 28, 2015. Good luck to all.
(Disclosure: Purchases made from Amazon affiliate links yield a small commission.)
(Sedum, Echeveria and daylily photos by Alan L. Detrick and Linda Detrick from “Essential Perennials,” used with permission.)