WHICH BEE BALM will really resist powdery mildew—and which of the endless parade of near-lookalike Heuchera (above) is truly a standout? At Mt. Cuba Center in Delaware, trial garden manager George Coombs aims to find out that, and more, about the fast-widening palette of native-plant cultivars being offered today–including what the  insects who have long relied on the straight species think of the newer garden varieties.

In the early 1990s, when I was working on a book called “The Natural Habitat Garden” with my friend Ken Druse, we traveled the country interviewing native-plant enthusiasts and photographing their gardens. One memorable stop was the home of Mrs. Lammot du Pont Copeland, outside Wilmington, which today is the botanic garden called Mt. Cuba Center, with more than 50 acres of display gardens on more than 500 acres of natural land.

I’d never seen native terrestrial orchids before, or the vivid red and yellow wildflower called Spigelia marilandica anywhere, and that day I learned that some discerning and forward-thinking experts such as Mt. Cuba’s first horticulture director, the great Dick Lighty, were already busy selecting “better” forms of native plants for garden use–a trend that has accelerated and become one of the hottest areas of contemporary plant breeding and selection.

Today, Mt. Cuba is open to the public from April to November part of each week, and also conducts more extensive research than ever: including formal large-scale trials of selected varieties of native plants such as Heuchera, Coreopsis, Baptisia, and Monarda for their garden worthiness, disease resistance and also for their appeal to the insects who have co-evolved with the plain old “straight species,” as the basic version of each plant is called.

George (above), raised on a large farm in South Jersey and educated at the University of Delaware, has been at Mt. Cuba about two and a half years, after working as a grower in the wholesale and retail nursery industry. In my latest radio program (listen in now), we talked about how he and the Mt. Cuba team take a closer look at native plants, and what they’ve been learning so far.

the mt. cuba center native-plant q&a

Q. Let’s start with a little more about Mt. Cuba, George.

A. One of the things we’re doing that’s exciting: We have a new ecological gardening certificate. We’ve offered educational classes for many years, but we’ve molded it into a curriculum where people can really get the full knowledge on how to use native plants in a meaningful way.

Q. So you manage the trial gardens—but home gardeners who are listening might wonder, “What’s a trial garden, as opposed to a landscape?”

A. A trial garden is more about making sure that plants are evaluated on an even playing field. So what we do is try to pick a genus that we want to examine further, and we’ll gather as many species and selections as we can find, and grow them all in one place.

The idea is that all these plants are experiencing the same weather, and growing in the same soil, and being cared for the same way, so you really can start to differentiate the pros and cons of each one, and how they can be used in a landscape effectively.

Our trial garden is about 15,000 square feet, and recently we’ve been able build a shade structure, so we can trial shade-loving plants as well. We’re very excited about that.

Q. I guess when it comes to gussied-up versions of native plants, I am sometimes a skeptic. I go to the garden center, and here’s this gorgeous new (fill in the blank)—for instance, coneflowers in new colors—and I want them all. But I bring some home and they turn out to be lousy plants sometimes. Maybe they were rushed to market too soon.

So when you do any trial, what are you looking for, really?

A. That’s exactly it: We want to make sure that when people buy these plants, that they have a good experience. It depends on where you are in the country; in different regions plants perform differently. We’re trialing plants from the perspective of the mid-Atlantic region. We want to be able to tell people, “These are the top 5 in this category that you can expect to succeed with.”

Q. Are there similar trialing programs around the country, in different regions? Like the one at Chicago Botanic Garden, for instance.

A. Chicago is one of the top places in the country, and they look particularly at hardiness—being in the Chicagoland area, since winter temperatures can get pretty extreme.

In the Southeast, the University of Georgia has a pretty extensive program with Alan Armitage–so a lot of things they’re looking for there are heat resistance.

The Denver Botanic Gardens, working with Colorado State University, trials plants for the Rocky Mountain region, which is a difficult growing environment as well.

Q. Do you all talk to each other?

A. We do—we’re generally not always trialing the same things, but I’ve talked to Richard Hawke at Chicago to get his feedback, so we can kind of build on where he left off, and try to avoid mistakes the other person has made.

Q. In some of your trials now, there is also an added scientific layer lately– explain that.

A. We’ve recently partnered with the University of Delaware, to add some academic research to how native plants interact in their environment. We’re trying to add an ecological layer to our evaluations.

Typically in the past we have always look at the horticultural; the ornamental. How long does it bloom; does it get any diseases; does it stand up after heavy rain?

Lately there is more interest, particularly with native plants, in what insects they support. One project we’re partnered with the University of Delaware on is studying how different cultivars of woody plants might impact the insects that feed on them, a study with Doug Tallamy where he’s looking at the straight species of a woody plant, and different cultivars to see if there’s a difference in the number of caterpillars or other leaf-eating insects.

A second project is looking at pollinator forage, and how different cultivars of native plants support honey bees and native bumblebees, and if there is a difference between what the bees prefer, or certain nutritional differences. [Above photo, a bee balm being evaluated.]

Q. So you’re putting labels on the “cereal boxes” that these plants represent to the insects. Fascinating! [Laughter.]

A. Exactly. It’s something that nobody has really looked at before, and it has been a big question in the native-plant community: Are cultivars good or bad? Are cultivars supporting insects like the straight species do?

So in Doug Tallamy’s project for instance, they’re looking at what happens when you change the leaf from green to purple, or you selected a cultivar for increased fruit production, or for fall color.

Q. So let’s go genus by genus—maybe starting with Heuchera. I think you told me you’re trialing 83 cultivars [top photo]!

A. We’re pretty much up to our eyeballs in Heuchera over here. [The list so far, with the first two years of trial notes.]

Q. This is one genus where I think it has gone too far, with all the cultivars.

A. It really has. We had an event when we started the Heuchera trial, and invited the breeders out here, and a lot of the breeders didn’t realize they had such similar cultivars on the market with somebody else’s product.

It was eye-opening to them, too, about how crazy we’ve gotten with Heuchera.

Q. I’m sure there is the hope to get a patent on a plant, to get royalties, or to have your own line of a plant or plants for economic reasons—so some of it is business-driven.

A. Yes, and nurseries in a relatively close competitive area where, say, there are five nurseries—they don’t all want to carry the same plants. Each one wants to carry something a little different from their neighboring competitors, to have a competitive edge.

Q. So what’s looking good from those 83 Heuchera?

A. The Heuchera have been difficult to judge, because a lot have performed well. We did have some difficulty with root rot last spring—late May, early June—we got a lot of rain here, about 12 and a half inches, which is normally what we’d get in an entire summer. We had a lot of rot, and after that we were able to determine some that really seemed superior.

One that’s doing well is ‘Bronze Wave’ [above], a greenish-purple one with a sturdy habit, well-rounded, and very attractive flowers—creamy-white, and there are so many of them that it’s an impressive display even from far away.

Others: ‘Color Dream,’ a silvery one. ‘Cajun Fire’ is a new one from Heuchera breeding central, Terra Nova Nurseries.

Q. Dan Heims, out in the Pacific Northwest.

A. That’s one of the really good ones. Also: ‘Citronelle,’ a really popular chartreuse one. Some others: ‘Steel City,’ ‘Southern Comfort,’ ‘Apple Crisp,’ which is a petite green one from Terra Nova that they’re marketing as a container type plant.

Q. I love Heuchera villosa—I just have the plain old one.

A. ‘Autumn Bride’ is a selection of it, and we’ve used it and the straight species pretty liberally in the garden for a more naturalistic look; they just blend in.

Q. What about the Coreopsis?

A. We’ve done that trial in two parts—perennial ones, and annuals. We just finished the annual trial after two years [link to the pdf report on the annuals here]. The ones that did best there: ‘Jive’ [above], ‘Salsa,’ ‘Pineapple Pie,’ ‘Little Penny’ and ‘Golden Dream.’

The problem is that the annual ones are so new, it’s hard for people to find them, so we’re hoping that our trials will bring some attention to them. [Photo of the annual trial, bottom of page.]

As far as the perennials go, we’ve been really disappointed with how they have overwintered here. Our soil is like a clay loam, a relatively heavy soil, which stays wet in the wintertime, so that’s not what Coreopsis like.

A lot of the newer hybrids that have a lot of C. auriculata and C. grandiflora in their parentage have done really poorly in our soil.

Some that have done really well include some of the C. tripteris. Also, ‘Show Stopper’ is one of the showier hybrids with a lot of verticillata in it; a nice bright fuchsia color, and similar in habit to ‘Moonbeam,’ which has been around a long time.

Some of the others that have done well: C. verticillata ‘Zagreb,’ and ‘Golden Gain’—those two are very similar.

Q. What about the trial of Monarda, or bee balms?

A. And they are definitely covered in bees! What we’re really looking for with the Monarda is resistance to powdery mildew. One we’re really excited about is Monarda punctata [above], a species people aren’t really aware of but we’re examining the garden potential of.

It’s covered in blooms right now, and instead of one crown-shaped flower, it’s a series of flowers stacked on top of each other. Covered in flowers, covered in insects; its common name is spotted horsemint.

There’s another species called M. bradburiana that’s just starting to take off in the marketplace, but that blooms earlier, like starting late May, a light pink-light fuchsia color that’s really promising as far as powdery mildew resistance.

A few of the cultivars that show promise: ‘Grand Marshall,’ ‘On Parade,’ ‘Grand Parade’ [above].

It’s definitely a struggle when you’re trialing 44 kinds of Monarda in one spot, but when you see ones that are resistant to mildew, it means a lot more.

Q. And the Baptisia?

A. We’re looking at them not for any particular problems, but because there are a lot of new hybrids coming out—different colors, and sizes [above, in the trial garden]. We’re examining how they grow over a long period of time. Baptisia are slow to mature, so we want to give them ample time to reach their potential.

We’re looking at which ones are good for compact situations, and have different flower colors.

Q. What’s next on the trial-garden horizon at Mt. Cuba Center?

A. We’re building up our collection of native Clematis, and also of sedges, or Carex, for future trials.

prefer the podcast?

GEORGE COOMBS of Mt. Cuba Center was my guest on the latest radio podcast. You can listen anywhere, anytime: Locally, in my Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) region, “A Way to Garden” airs on Robin Hood Radio on Monday at 8:30 AM Eastern, with a rerun at 8:30 Saturdays. Get it free on iTunes, the Stitcher app, or streaming from RobinHoodRadio.com or via its RSS feed. The July 21, 2014 show can be streamed here now. Robin Hood is the smallest NPR station in the nation; our garden show marked the start of its fifth year in March, and is syndicated via PRX.

(All photos courtesy of George Coombs and Mt. Cuba Center; used with permission.)