‘THEY BRIGHTEN our days just as summer heat and humidity become tiresome,” reads a line in the new book “The Art of Gardening,” from Chanticleer Garden in Pennsylvania, and the “they” in that statement refers to hydrangeas.  These generously flowering shrubs are some of my favorites in the fall garden, too, when those big blooms often fade in the nicest and most colorful ways, as do the leaves of many Hydrangea species and varieties.

But which ones to choose from among the daunting selection out there, and how to care for them, anyhow? I’m so often asked about the particulars of pruning and of soil chemistry when it comes to the genus Hydrangea, so for all those questions and more, I invited Chanticleer’s Eric Hsu to my public-radio program.

Eric became plant information coordinator at Chanticleer in 2011, and before that came stints at some of the most prestigious woody-plant collections in the Eastern United States: Scott Arboretum of Swarthmore College; the Arnold Arboretum of Harvard University, and the Polly Hill Arboretum on Martha’s Vineyard.

He has his bachelor’s from Cornell, and master’s degrees from both the University of Reading in England, and the University of Tasmania in Australia.

At Chanticleer, in Wayne, Pennsylvania, Eric is apparently referred to as the plant geek, and is a frequent contributor to “The Plantsman,” the prestigious quarterly published by the Royal Horticultural Society in the United Kingdom. He’s also one of the Chanticleer team that contributed to the lavish new book.

Read along as you listen to the Sept. 14, 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).

my q&a on hydrangeas, with eric hsu of chanticleer

Q. What’s a “plant information coordinator?”

A. Basically my job as a plant information coordinator is a dual role as an educator and a plant curator. As an educator I produce these monthly plant lists that inform visitors what are plants of interest—whether they’re in flower or in foliage. At the same time I maintain plant records for the garden, and it’s a challenge because we don’t have labels in the strict sense that a botanic garden has. I’m always chasing the gardeners to see what they’re adding or they’re taking away.

It’s a constant struggle between communication and updating records.

Q. Knowing the gardens at Chanticleer, which are constantly ebbing and flowing with additions and subtractions and big beds being changed out—that must be a big job, keeping after the gardeners. [Laughter.]

So on to hydrangeas, Eric: To most people you say “hydrangea,” and they think, “blue flowers.” I should confess: I’ve never grown a blue hydrangea! But let’s start with the hydrangeas that produce those blue flowers–forces willing–the mophead types.

A. Those mophead hydrangea, as everyone thinks of them in pop culture, are actually Hydrangea macrophylla—which means big-leaf hydrangeas, so you can get a sense of the species in its name. The leaves are really big, they’re tough. And they’re native to maritime regions of Japan, which is often where you find them doing best—in seaside gardens.

Hydrangea macrophylla became very popular when they were first introduced to Europe and North America, when Japanese plants were all the rage in Western horticulture.

Q. Like I said I’ve never grown any–and mostly that’s because I’m in Zone 5B and when I began the garden decades ago, I didn’t think they were reliable here–the ones that were available didn’t do well in our hard winters. Let’s talk hardiness—I know at Chanticleer you have been re-evaluating some of your macrophylla, even though you’re a zone or two warmer than I am.

A. The catch was we had a series of mild winters, which were ideal for flowers, year after year. Then the last two years we had these harsh winters, which took us a zone down—sub-zero temperatures, no snow cover. That meant all the wood that was produced the previous year was killed outright, which meant no flowers.

As you know, the issue is that big-leaf hydrangeas often produce on the previous year’s wood, so if that is killed, it means no flowers.

Q. Right.

A. I’m not surprised you haven’t grown the blue hydrangea—it’s almost that elusive goal, like the blue poppy.

Q. [Laughter.] Elusive goal—then I don’t feel so bad. Frankly another reason I’ve never grown one is that blue isn’t a big color for me.

So you just pointed out something very important, that’s not the same for all species in the genus Hydrangea. But the big-leaf ones carry their flower buds over the winter on last year’s wood—yes?

A. Yes, so if you remove those—if you prune those by accident, or you had a very hard winter, you’re basically seeing a flowerless shrub next year.

Q. So if you prune incorrectly or you had a horrendous winter that literally hipped it in the bud—goodbye, flower buds for the following year. What are you doing at Chanticleer? You have some really big areas of blue hydrangeas. Are you considering swapping some out for hardier varieties since our weather seems to be a little less predictable, or what?

A. What we’re doing in the Gravel Circle, where visitors often marvel at the cherry blossoms in spring, we have our large collection of big-leaf hydrangeas along with some paniculate hydrangeas.

The majority of big-leaf hydrangeas did not flower the last two years, except for one or two that were more in protected areas. We felt that because the area was such a big show, and not having that show reliably the last two years, we had to re-evaluate and think of alternatives that would be reliable flowers for us.

Q. Will you go with other hydrangeas, to have that big blue look, or what are you going to do?

A. We’re hoping to diversify, so basically instead of relying straight outright on big-leaf hydrangeas, we want to consider other hydrangeas that are not a commonly known but still provide a really good show.

We’re looking at serratas [above], which are not as showy as big-leaf hydrangeas but they’re still very attractive. We want to increase more of the paniculatas and involucratas. These are hydrangeas that don’t get the attention the big-leaf hydrangeas do. They’re not as big and bold; people want big blue flowers. Unfortunately these may not have the same blueness, but they will still provide a reliable display for us.

Q. What are these flowers shaped like—not a mophead like the big-leaf types?

A. More of a lacecap.

Q. And this is the species Hydrangea serrata, I should say.

A. The serrata types tend to have more of a lacecap; they’re not as full. When we say full, we’re talking about the sterile flowers, not the real flowers. The lacecaps tend to have sterile bracts around the real flowers.

Q. The color palette of the serratas?

A. The range is just like the macrophylla—a kaleidoscope. You can get from whites, blues, purples—depending on the soil pH as well.

Q. You bring up the next most frequent question about hydrangea—after why didn’t my hydrangea bloom? The next most common: How do I turn them blue? How do we?

A. Everyone wants blue, and it really comes down to soil pH. A lot of people buy them as pot plants, and it’s blue in the container. They plant it, and next year in the garden it’s pink, and they say, “What happened? Did it change color?”—like a magical scientific experiment.

It really comes down to soil pH. If your soil pH is basic, on the high end, your hydrangea is more likely to flower pink. However, if you’re more on the acidic end, low pH, it’s going to be blue. If you’re in between, you’re going to get a flower that looks almost like it can’t make up its mind what it wants to be.

Q. Do you amend the soil at Chanticleer, or do you have an acidic soil?

A. Our soil tends to be more on the acidic side, so we don’t have problems with the blue colors. But I think given the fact that we really prefer not to amend the soil each year for the desired color, we just let the hydrangeas show their true selves.

Q. Pruning can affect the bloom, but sometimes we need to reduce the size or they’re overgrown and too thick. When and how do we prune, if we have to?

A. I would advise pruning them in late winter or early spring, when you can actually see the structure. It’s basically like pruning any shrub: You want to prune out the diseased wood and the weak wood, and leave the strongest ones standing. You also want to see the buds, and see if they’re still firm and green. Oftentimes it might be hard to tell in late winter, so we might prune in midsummer, and just take out the twiggy growth then that’s impeding the plant’s overall structure.

Q. What’s not going to develop into anything worthwhile—that’s crossed inward, and so on.

A. It’s basically the common philosophy you apply to most shrubs: You do a lot of deadwooding—we take out dead wood, we take out diseased wood and improve air circulation. Hydrangeas can get mildew if they’re not in areas of good air circulation.

Q. We talked about the species serrata as an alternative to the big-leaf types. But on the cusp of fall now there are a couple of other species that are really having their moment: H. paniculata (from Asia) and also the Southeast U.S. native H. quercifolia.  They’re different in the way that they grow, and the way that they look—there’s no blue holy grail with those. [Laughter.] [Below, the quercifolia cultivar ‘Snowflake’ at Chanticleer.]

A. No, unfortunately I’m afraid not; no blue. But they do have other redeeming traits that make them worthy of a space in your garden.

Q. They do.

A. We love Hydrangea paniculata because they bring such a welcome dose of fresh color—white, especially in the hot, humid days. And they’re reliable. You can prune them hard, or leave them unpruned, and they will still flower year after year. And they have the added advantage of having flowers that age to pink and burgundy as we get later in the season.

They are really wonderful plants—and I know that people are overwhelmed by the flood of cultivars right now.

Q. I am, I have to say.

A. I know you grow quite a few yourself.

Q. I do—and the funny thing is I have some that are so old, that I have had for at least 20 years, like a straight Hydrangea paniculata. It’s not a named cultivar, but the species. And they I have another one that makes big trusses later on, called ‘Tardiva.’ But I don’t have a lot of others—and there are so many now, with smaller or larger or slightly different color flowers, and time of bloom. Any favorites?

A. There is one we love called ‘Quick Fire,’ that we grow in the prairie dropseed beds, where we have it growing with bald cypress and switchgrass, Panicum virgatum. It’s a great autumn combination, and I always admire it whenever I am walking through the grounds at Chanticleer.

Q. And you love ‘Quick Fire’ because…?

A. It’s one of the earliest to flower, in mid-June, and as soon as it flowers, it quickly ages to a pink and burgundy color. Right now our plants are looking like they’re really on fire—hence the name ‘Quick Fire.’

Q. And you hinted that you could prune them or not prune them. I have one paniculata that I have neglected for the last few years, the one farthest from the house; maybe it’s a ‘Tardiva.’ It’s so gigantic now, and when people come for tours they ask, “What’s that?” And I say, it’s just a hydrangea that I never prune any more. It’s massive, but each individual flowerhead is smaller than on the one that I prune regularly, harder, each year.

Does how hard you prune affect flower size and number of flowers?

A. It’s funny: Some people say there is no difference between unpruned plants and pruned plants in terms of flower size, but I think sometimes there is. If you prune them really hard, you get these really big shoots—almost like the water shoots you get from pruning trees. And the flower can be enormous—and almost look unnatural in the garden, though I suppose that’s a matter of taste.

Q. What about the Southeast native oakleaf hydrangea, Hydrangea quercifolia. Do you grow that? [Above, oakleaf type in fall foliage color.]

A. Yes, we like to use it in our native woodland gardens, especially in the area called Bell’s Run. Hydrangea quercifolia is great for this areas because it takes the shaded understory. Just like paniculata it flowers white, so it is very refreshing in the shade. A lot of people don’t know this but it’s got great exfoliating bark, which we like for winter interest—almost like a paperbark maple, in a way. The fall color is fantastic—almost like a wine color, and when it’s hit by the late autumn light, it’s luminous.

Q. When do we prune the oakleaf, or do we?

A. You would not prune the oakleaf hydrangea [above, in winter] the same way you prune the paniculata because they don’t take it very well, and tend to flower on the old wood. Pruning it is like pruning any shrubs that resents pruning—if you prune it, it is going to rebel at you, and will not do well.

Q. Uh-oh, it’s going to rebel? [Laughter.] So we do the minimum we have to do; clean it out if it needs it, like crossed branches, but basically we let it do its thing.

A. Exactly. You wouldn’t prune it hard like a paniculata.

Q. It has great fall foliage color; most of the hydrangeas do, but this one has a lot of reddish, and it’s a beautiful shape.

A. And it’s really heat and humidity resistant.

Q. Owing to its Southeast origins.

I want to make sure we put in a mention for our other Southeast native species, Hydrangea arborescens. People probably know the cultivar called ‘Annabelle’ best. Do you grow it at Chanticleer?

A. Yes, we do, and we also grow the sub-species radiata, which has silvery undersides. They’re very happy here, and in fact self-seed for us. We do have to edit plants out where we don’t want them.

Q. I always think of ‘Annabelle’ as a friend at Wave Hill public garden in New York City used to say: She’s a girl who need a corset; she needs to be propped up a bit. She’s a little too zaftig. [Laughter.] Do you prune them hard—which they can be if desired—or support them in some way?

A.  We try to minimize interventions. And we don’t prune our Annabelles hard, we let them come through. Having said that, we do mow down the plants in the parking lot, because it’s drier there and the panicles are not as big and they don’t tend to flop. However in a regular garden setting, I think it’s always prone to flopping, no matter what you do. It’s the small price you pay for the gorgeous, big white blooms.

Q. Or you build her a corset of bamboo and twine—but as you say, you don’t want to do too may interventions.

A. It’s part of our philosophy to demonstrate techniques that are accessible to home gardeners. We don’t want to be fussing over plants so that it’s not realistic, and we do have a lot of extensive grounds—and don’t always have time.

Q. Kind of like me here at home, Eric Hsu.

 enter to win the chanticleer book

I’LL BUY A COPY of “The Art of Gardening: Design Inspiration and Innovative Planting Techniques from Chanticleer,” for a lucky reader. All you have to do to enter: Comment in the box at the very bottom of the page, after the last reader comment, answering this question:

Is there a hydrangea that you rely on particularly in your garden, and why?

I definitely heave a sigh of relief when the paniculata types start blooming, and as Eric says in the interview seem to freshen up the place in high summer, when it can be otherwise tired-looking.

No answer, or feeling shy? Just say something like, “Count me in,” and I will, but an answer is better. I’ll select a random winner after entries close at midnight on Sunday, September 20. Good luck to all.

(Photo credits: Eric Hsu portrait by Panayoti Kelaidis. Shot of chairs, walkway, serrata detail and winter garden from The Art of Gardening© Copyright 2015 by the Chanticleer Foundation. Published by Timber Press, Portland, OR. Used by permission of the publisher. All rights reserved. Photo of paniculata with Chamaecyparis and of H. quercifolia by Lisa Roper, courtesy of Chanticleer.)

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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 Sept. 14, 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).