organic rose care, with scott arboretum’s adam glas

I CONFESS to a decided dearth of roses here in my northern garden, with only a few species types in residence, but Adam Glas is positively surrounded by them daily in his job in the Dean Bond Rose Garden at Scott Arboretum in Pennsylvania.

Adam, a graduate of the prestigious Longwood Gardens Professional Gardener Training Program, joined the staff at Swarthmore College’s arboretum in 2012. The rose garden he’s responsible for was first designed in 1956, then recently renovated to be more sustainable. In a recent chat, Adam shared tips for organic rose care today, both cultural techniques like proper spacing and using fish hydrolysate as a feed and disease-preventive, and also advice on selecting more resistant varieties. We even talked about the dreaded rose rosette disease that has been on the rise in recent years.

If you’re near Swarthmore in late May and early June, treat yourself to a rose-garden tour, or just listen along as we get a virtual visit with the resident expert. Read along as you listen to the May 22, 2107 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).

More about visiting the Scott Arboretum in Swarthmore, Pennsylvania, is at this link, and events are listed in their calendar.

growing roses organically, with adam glas of scott arboretum



Q. I want to start with a brief background on the garden, and also you: Did you know you’d become a rosarian? You studied horticulture, but was that the direction you were headed in, or did it just happen?

A. It just happened. Having the rose garden here at the Scott Arboretum, it was just sort of a natural progression into roses—not something I necessarily looked forward to taking on initially, but I’m happy that I have now.

Q. So you’ve kind of warmed up to them. [Laughter.]

A. Yes, absolutely.

Q. And a little bit about the garden: as I mentioned in the introduction, it was first designed in the 1950s, so paint a picture of it for us. Is it a traditional-looking rose garden?

A. Initially when it was designed in the 50s, as you said, it was a traditional design. The original garden was laid out in five beds. There was a bed designated to species roses, another two beds for climbers and shrub roses, and then two more beds that were just grandifloras, hybrids teas and floribundas. There weren’t any other types of plants; just roses. So a very traditional rose garden.

Q. I feel like in the pictures I have seen…is it surrounded by the more traditional posts and chain swags? Is there like a border around it?

A. It actually sits right in the middle of campus; right in the heart of campus. And it sits right in the middle of a big lawn. It does feel a little bit exposed when you are in there, but there is that post-and-chain structure that creates a little sense of enclosure when you are in there.

Q. Originally there were these five beds, and they were divided by class of roses, and it was all roses. Do I take it to mean there is no underplanting—just mulch or something—or are there herbaceous plantings underneath the roses today?

A. Correct—originally it was just roses and mulch basically [laughter], but recently we have transitioned to a more dynamic planting scheme. Roses typically bloom heavily in late May-early June here in the Delaware Valley region, and then they take a break and flower again in late August and into September.

So for many reasons we wanted to create a little bit more of a dynamic space. We’ve added shrubs and perennials, and a few annuals as well, as well as about 120 different varieties of Clematis.

Q. Oh my goodness. Did you say 120? [Laughter.] [Above, ‘Home Run’ rose with ‘Blue Pirouette’ clematis.]

A. Give or take; it’s not a precise number, but there are a lot.

Q. How many kinds of roses are there?

A. There are about 160 different varieties of roses in there. We’ve got species roses, shrub roses, hybrid teas, grandifloras, floribundas, climbers—you name it, we have it. [Laughter.]

Q. Are there multiples of each one?

A. Yes, typically there are. As we’ve moved into a more sustainable approach with the garden, we’re trying new roses–new genetics and new breeding in roses, with roses that are supposed to be disease-resistant and very adaptable for this region. A lot of times we’ll try one, to see how it does, and we may get a few more if it does well.

Q. You mentioned “sustainable,” so when did this renovation or whatever you call it—when did this happen, and how long in the making was it? I know you are involved with various sustainability projects that pertain to roses as well.

A. Exactly. They have been trying to renovate and rethink the rose garden for about 10 years now, and when I started here at the arboretum about five years ago, I was approached with the concept of renovating the rose garden. I was excited for the opportunity—but also along with that, the college has a really strong role in sustainability, so we wanted to do it in a more sustainable way.

It is maintained organically now. We used to go in there every 10 days and do different cocktails of fungicides to control disease, but now it is completely organic. So we have gotten away from what you would consider a traditional rose care.

Q. So that must have been a pretty massive shift: Here you are describing it as in the middle of campus, and in the middle of a lawn—it’s seen by a lot of people all the time, and you can’t have it all defoliating and looking horrendous, right?

A. [Laughter.] Right.

Q. I mean, this is conspicuous; it’s not hidden in the back corner somewhere.

A. Absolutely.

Q. To accomplish that, were there changes to the soil—I mean, what happened? Did you dig out plants, or was it just a change in the cultural practices? 

A. Sort of all of the above. A lot of the roses were way too close together; they had overgrown a bit. The first year in the transition, I literally just spent pruning, removing suckers, and spacing roses out.

Along with that, we did change the bed configuration a little bit, expanded some of the beds, moved some of the beds a little bit. But the footprint basically remained the same.

In terms of the soil, the soil in there is beautiful. Since the garden was planted in the 50s, we add about 3 or 4 inches of leaf compost-wood chip mulch mix yearly, so the soil structure is wonderful and lovely. That’s a huge advantage going into this type of system: to have a good soil base to work off of.

Q. Before we go to the next step, you said first year you spent pruning and spacing. For people who don’t know, a lot of rose “problems” come from fungal things, so air circulation—getting plenty of light and air—is like an antidote to that. Is that sort of the basic idea of what you mean when you say you spent this time pruning and spacing?

A. Light and air infiltration is critical in terms of a lot of the fungal pathogens that roses can get, especially black spot. Black spot is the biggest issue in our region with the roses, keeping them healthy and happy. That also allowed us room to incorporate other plant material. We’ve incorporated Clematis, but we’ve also incorporated perennials and some other shrubs. Initially the entire plant list for perennials and shrubs that we introduced, all of them had traits that were attractive to beneficial insects and pollinators as well.

Q. Interesting.

A. We were trying to create a more healthy ecosystem in there.

Q. So you were sort of diversifying this community, this little habitat, of the rose garden. Give me some examples of perennials and shrubs that went in there that did this beneficial-attracting thing.

A. A lot of shrubs we chose were ones that bloom offseason from the roses. So viburnums that were blooming very early, to draw some early pollinators in there, and some Spiraea and lilacs as well. We’ve incorporated a few Itoh hybrid peonies in there that bloom early as well, and also salvias and Achillea and geraniums—perennial types–that might extend the interest season as well as attract pollinators also.

Q. So you are having not just these two big moments of bloom and otherwise not much going on, but you’re having a more sustained floral display on all the levels, from much earlier to the very end of the season.

A. I like to think it is a much more interesting, dynamic garden as opposed to a static rose garden.

Q. I sort of derailed you. The first year you did this pruning and spacing, and the soil’s good, because the protocol—even when you were doing the chemical cocktail to counteract some diseases—was that they were also doing a good thing, adding multiple inches of mulch that was breaking down. So what happened next after the pruning and spacing and diversifying? What other elements were there to the sustainability project?

A. Then sort of came the baseline we established here as to what was acceptable in terms of disease.

Q. Right.

A. Like I said earlier, especially in terms of black spot, when you’re maintaining a rose garden specifically in an organic manner, you have to establish a threshold of what’s acceptable and what isn’t, in terms of your aesthetics. The next few years was really evaluating the roses, and seeing how they were responding to the new system, and whether or not they were a good fit for this program.

Q. Uh-oh. [Laughter.]

A. If they looked good, great; if not [laughter] they get the compost pile.

Q. Did they feel the pressure? I think they knew what you were doing, looking at them sideways. You knew that once you established the new regimen, that you had to be kind of cutthroat about who worked and didn’t in this new protocol.

So you did a couple of years of that, and even though some had been pruned and spaced and given these companion plants, some still didn’t cut it.

A. Exactly. Roses, like I said, are so regionally adaptable. Something that’s bred in California, somewhere hot and dry, they’re definitely not conducive to growing in the humid, moist summers that we have here.

Q. That’s important for people listening elsewhere in the country. You’re mid-Atlantic. When figuring this out—this part of the adventure that you’re talking about now—one has to really do research and not buy 20 of one thing, but test them out. Try something, see how it does for you, inquire at botanical gardens in your area if they have a good rose garden—what insights can they give you? You’ve got to look for clues.

A. When we were going through this process, we worked closely with New York Botanical Garden because they have a lovely rose garden there that is also maintained in a more sustainable manner. But even the difference of 100 miles—we’d try roses here that were doing really well there, and they just did not perform for us.

Q. Did you note that some classes—I keep using the word classes, but I’m not sure if that’s right—are less disease-resistant or more so? You talked about species roses and climbers and shrubs and grandifloras and hybrid teas and floribundas. Are there some groups that are like: “These are the ones that are weakest.” Or is it all over the map?

A. It was a little bit all over the map. I tend to see the ones that haven’t had a lot of breeding and genetics in their background tend to do a little bit better. More of your species roses, or something that has a little more of a pure line of genetics tends to be a little more disease-resistant.

It just has to do with breeding for specific traits. Most of our roses are bred for the cut floral industry; they’re not necessarily bred for the garden. Breeders and hybridizers are getting away from that and are focusing on producing sustainable roses that do grow well in the garden.

Q. Do you want to tell us some that you adopted or maybe cast out? [Laughter.] Winners and losers? Any that you found have really done well for you?

A. I certainly have my favorites for many reasons [laughter]. ‘Summer Sun’ has really done well for us. It’s a floribunda rose, and I planted it two years ago, and it has just done really, really well. It’s a lovely orange sort of mixed-yellow rose that has just really performed well for us. [The rose fades to pink, above.]

‘Home Run’ is sort of the base of a series, and that one has done really, really well. It’s a shrub rose, and flowers for a really long period of time. It’s a nice single red rose, and very disease-resistant and very sturdy in the landscape.

Q. Does it come from a well-known breeder?

A. I’m not sure who hybridized it, but they are starting to develop new genetics in that series. We just got sent a few to try that haven’t been introduced yet, so hopefully they’ll do well and they can introduce them to the market.

Q. So those are two winners.

A. A climber that has done really well for us is ‘Cloud 10.’

Q. ‘Cloud 10.’ [Laughter.] I was going to say: It must be white.

A. It’s definitely white. With a lot of these roses that they are breeding for sustainability and disease-resistance, the fragrance tends to be the first trait that gets lost. But this is one that has a really nice fragrance. It’s a pure white flower, and heavily double and a pretty good climber and has done really well for us. Actually the hybridizer who developed Knockout roses developed this rose.

Q. So those are some of your treasures. You just mentioned a climber, and those pillars or swags we talked about at the perimeter of the garden—is that what they are trained on?

A. All of our climbers are on that post-and-chain system. We do have a couple of other trellises within the garden that we are starting to train some roses on, but they are mostly designated for Clematis at this point.

Q. You must have a fairly substantial collection of climbers, with all those posts and chains.

A. I think there are about 20 climbers in the rose garden right now.

Q. I saw in the nice little brochure [pdf version] about the garden a rose I used to have called ‘Veilchenblau,’ a bluish-lavender colored climber, yes?

A. It’s a rambler.

Q. A rambler. Do you still have it?

A. We do still have it, and it’s lovely. I’d say the nicest thing about that one is it’s nearly thornless. So if you are scared away from roses because of thorns, that’s one you might try.

Q. [Laughter.] I’ve seen it trained up onto a pillar, like a more vertical thing, and I have also seen it like a big octopus—a big, open thing. It’s quite a beautiful color, that lavender-blue.

Another one I love because it gives more than just the flowers is the blue-leaf rose. I don’t know if it’s called Rosa rubrifolia or glauca any more, but do you grow those?

A. I agree; it’s one of my favorites as well. Roses typically tend to be a one-season type of plant, but that’s a four-season rose. You’ve got really lovely blue-gray foliage, and nice flower—a single flower, and only flowers once with a nice pink flower. And then in the fall you get hips as well.

Q. I want to ask about fertilizing—and I know you don’t do nuclear-holocaust-y stuff anymore [laughter]. Are you feeding organic rose foods to these plants?

A. We actually use fish hydrolysate; that’s our disease control as well as our nutrients.

Q. Fish hydrol…what?

A. Fish hydrolysate. It’s basically fish oil, and through the growing season we spray that on about every 10 days. It definitely stinks when it’s wet, but as soon as it’s dry you don’t notice it.

Q. [Laughter.] Interesting—and it’s a food as well as a preventive.

A. It’s basically fish oil, so it kind of creates a little bit of a surface on the leaf so fungal spores and pathogens don’t really have a chance to land and germinate.

Q. Never heard about it; fascinating. I don’t suppose any conversation about roses in this time in history can happen without asking you about rose rosette disease. Big plague in the industry right now.

A. Unfortunately, there is not a whole lot that you can do about it. Once the rose has it, our recommendation is to remove the rose and destroy it. Providing proper cultural care as well as pruning properly, and good spacing of the plant—good healthy plants—is the only thing you can do. It’s spread by a little mite that travels by the wind.

Q. Oh, it’s a mite.

A. An eriophyid mite. So it’s pretty random if you get it, but unfortunately it’s pretty devastating, and there is no control once you have the disease.

Q. And when you say “destroy,” you don’t mean put it in your compost heap; you really mean destroy.

A. I’ve heard of people burning it, or doubling it up in a bag and sending it off to the landfill, that kind of thing.

Q. And it shows itself as sort of this kind of disfigurement?

A. The growth that happens is very contorted growth, and the internodes are really short. It’s kind of gnarly looking, and the foliage is typically red—definitely different in terms of foliage color from the normal rose.

[Read more about how this virus that’s transmitted by mites affects roses, and what is known about it, with photos.]

Q. I haven’t seen it, but it is something my readers and listeners ask about a lot and have suffered through. Tricky stuff.

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 May 22, 2017 show using the player closer to the top of this page. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).

(Rose and garden photos courtesy of Scott Arboretum, by Adam Glas and Rebecca Robert; photo of Adam Glas by Alexis Bacon.)


  1. Wendy says:

    Great interview with Scott on growing roses organically! I was waiting for a question concerning Japanese Beetles, but it never came. Is there any “new news” out about the best way to keep them at bay?

  2. Tom Rozier says:

    In our garden in southern middle TN, we grow ‘Thomas Affleck’ and ‘Lady Pamela Carol’ (shrub roses); “Westerland’ (floribunda); ‘Mrs. R.M. Finch’, Cl. ‘Pinkie’, and ‘Marie Pavie’ (polyanthas); ‘Caldwell Pink’ (found rose); ‘Penelope’, ‘Danae’, ‘Prosperity’, ‘Buff Beauty’,’ Cornelia’, and ‘Darlow’s Enigma’ (hybrid musks); ‘Veilchenblau’ (hybrid multiflora); and Cl. ‘Don Juan’. We feed with organics–compost and pine bark and either Mill’s Magic or Espoma Rosetone. We buy our roses from Antique Rose Emporium in Texas.

  3. Dianne says:

    I love roses. Sadly I’ve lost all of mine to the rosette disease. I had lots of David Austins old English type, a 20 year old New Dawn and numerous others. All gone. I mourned them for a year or two and then turned to vegetables!! Now okra grows where the New Dawn was and muscadines inhabit former rose territory. Elderberry now resides where another climber was. And all my energy now goes to keeping up three raised veggie beds. Not as pretty and fragrant as roses but a nice trade off at the table. I miss my roses but love my new found passion.

  4. Marni Crabtree-Davison says:

    Great color and texture combinations-especially love the allium with the roses! Great job my friend!

  5. Jody McGowan says:

    Hi Margaret,

    I second Mike G.’s comment — more information, please, about the protocol used by Adam to care for the roses at Swathmore. Products used, application rates, frequency, etc.

    Also, would love to learn whether any studies have been published about organic management practices for roses and gardens in general. I have gone organic but there are definite challenges and it is a lot more expensive. It would particularly be great to hear a podcast on organic turfgrass management. Where I live (in the D.C. metro area), it is very hot and humid in the summertime compared to the northeast, which is hard on our turf.

    Thanks — as always!! — for supplying us with a wealth of gardening info.


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