materials for path surfaces, black spot and powdery mildew, and more: q&a with ken druse
IT’S URGENT GARDEN QUESTION time again, which means Ken Druse visited my radio show and podcast to help provide the answers about topics ranging from good and bad materials for making garden paths, to issues with powdery mildew on various plants, and roses with black spot and even a question about transplanting ginkgo seedlings—or not.
Longtime friend and fellow garden writer Ken was just back from a garden-filled lecture trip across the nation, with stops at Minnesota Landscape Arboretum and in Northern California when we spoke. That’s an exceptional private garden in Piedmont, above, that he visited.
Read along as you listen to the July 15, 2019 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Spotify or Stitcher (and browse my archive of podcasts here).
q&a with ken druse: ken’s recent garden travels
Margaret Roach: Hi, Ken.
Ken Druse: “Across the nation,” that sounds wonderful. [Laughter.]
Margaret: It was. Wasn’t it fabulous? It was a whole thing, a road trip. No.
Ken: Right, right. I was at Newark Airport. Yes, that was half the trip.
Margaret: Garden capital of the … Oh no, yes. But you did.
Ken: Yes, go ahead.
Margaret: You’ve been traveling.
Ken: I went to California, mostly to see friends, because I figured if I’m going to Newark Airport, I might as well go to California, even though I didn’t have a lecture in California. Then I went to Minnesota after that where I did have two lectures at the Minnesota Landscape Arboretum, which is incredible. And they have something like 800,000 visitors a year, and it’s garden after garden after garden, and 1200 acres, and fruit testing, because it’s allied with the university. I was blown away. It was really hot, though, I have to … Well that’s everywhere, right? [Above, the Japanese Garden at the Arboretum there.]
Margaret: Yes. But still. So you had never been before? I’ve never been there.
Ken: Well I’ve been to Minnesota. I’ve been to Minneapolis, St. Paul, but I’d never been there.
Margaret: To the Landscape Arboretum.
Ken: Right, and the Andersen Horticultural Library is part of that. It was really something. And the apples … acres and acres of … They’re trying to have wine grapes, but that’s another story. That’s where the ‘Honeycrisp’ apple was developed, which is becoming one of the most popular-
Margaret: Absolutely, yes.
Ken: Absolutely. And they have this amazing thing. They do so much research. But Margaret, I wanted to tell you, they are doing DNA … Well they test the DNA of seedlings, and they can tell from a leaf whether it’s going to be crisp, and how long it’s going to keep, and whether it’s going to bear fruit early. So they don’t always have to grow the thing on to have fruit to know whether it’s worth saving. [The University of MN’s marker-based breeding program is explained at 2:29 in the video above.]
Margaret: It’s that crazy? Yes, brave new world, baby. [Laughter.] Wow. And then you said California, you went to California as well.
Ken: Yes, I was in California first, in Northern California, just visiting friends. And I went to the Berkeley Botanical Garden, which is wonderful, as always, and hot. [Laughter.] But then I went to a private garden in Piedmont, a garden I’d never seen before. [Photo of a section of the garden, top of page.] I don’t know if you’ve ever been to the San Francisco area. Piedmont is east of Oakland.
Margaret: I’ve been with you, Ken Druse. We’ve traveled there together. You’re just teasing. You don’t want to tell people that we’ve traveled the country together. [Laughter.]
Ken: No, I was asking the listeners if they’ve ever been.
Margaret: Yes, O.K. Yes.
Ken: But it’s so incredible to be able to … They can grow a lot of apples, they can grow some lilacs, because it gets cold enough to have these things. But also, it freezes. They have a killing frost every 30 years. But this garden had a Brugmansia collection, you know brugmansia, the angel’s trumpets [above].
Margaret: That we Northeastern gardeners have to store in the cellar in the winter, right?
Ken: Sometimes they’re alive when …
Margaret: Yes, sometimes.
Ken: This guy had I don’t know, 20 different kinds? Two different variegated ones, really amazing.
Margaret: Wow. Anything else? Anything that we grow that they grow?
Ken: That’s the thing, because it does get cold enough. At one point the home owner was testing me. I didn’t know I was being tested. He said, “Do you know what that is?” And I did. “That’s Astilboides.” And then he asked me, “Do you know what this is?” I think it was Diphylleia cymosa or something like that. And he turned to the people I was with and he said, “Oh, he’s pretty good.”
Margaret: [Laughter.] I have that plant. I have both those plants.
Ken: I know you do. I always think of you … I can’t look at Astilboides without thinking of you. But then they showed me Syneilesis … Well they said it was Syneilesis, and I had to correct them. I said, “That’s Ligularia japonica,” which is a very easy to grow, wonderful plant that I have grown for years. And you don’t see it very often in gardens, which is kind of terrible because it’s terrific. It has divided palmate leaves. It has these funny garbanzo beans on wands before it blooms. But the leaves there were, I kid you not about 18 inches across, and my leaves are 10 or 11 inches across. [Foot-wide leaf detail of Ligularia, above.]
Margaret: With all the rain we had this spring, I would say—I grow it also—and I would say mine are maybe not 18, but close, some of them, some of the bigger leaves. So, to give people an idea, it has this clump of … from which emanate these beautiful fringed, as you say, hand-shaped, but fringe-y kind of leaves, very elegant and very dramatic. And what I did with it, I have these big areas of hellebores that they flower early in the … early, early spring, and they have evergreen-ish almost foliage. It’s nice, but it’s nondescript. So I wanted to break up the masses.
And so I made spaces every so often in this big, big, big old bed of hellebores. I put a number of these Ligularia japonica, and as they’ve come into their own, it’s like this beautiful fringe-y palmate foliage. It kind of comes up above the sea of green hellebore foliage ad this time of year. And then as you say, it has these little strange garbanzo bean bud-y sort of things, and then yellow daisies, gold daisies up top, way up high, they’re tall when they’re in bloom, right?
Ken: Right. That sounds really great.
Margaret: So it’s kind of a punctuation thing, in the way that you punctuate your landscape very beautifully on a larger scale: You’ll have columnar trees every so often or something. But it’s like a miniature version of that, it’s not columnar, but it’s like contrast-y, but it’s not competing with it. It works. And when the hellebores are doing their thing, the Ligularia [above] isn’t up enough to besmirch them, do you know what I mean? So it kind of works, right?
Ken: How moist is it where you have it growing?
Margaret: Well you always tease me, because I’m on the bottom of a hill, on the downslope of a hill, so I probably have good moist soil. But it’s not very. It’s not very. It’s under a big, big, big old apple tree, like a 140-year-old apple tree. So, it gets shade. But it’s just fun, and I just did it kind of … I don’t even know why, it was semi-consciously, and it works because there are opposite seasons that they do their things. So again, the Ligularia is not out covering up the hellebores below it, right? It’s resting kind of above the hellebore foliage, and it makes a punctuation. So it’s kind of fun.
So they grow that in Northern California, interesting.
Ken: I’d never seen it there before, and they were showing me like it was … Well they said it was Syneilesis, which it wasn’t. They were showing it off as this very rare thing. And as you’re saying that I’m realizing, I’m growing this thing practically in no sun. And you have it in shade. And I have it in a moist place, but I’m going to divide it. I’m going to copy you.
Margaret: Yes. I think it’s an interesting one, if you have a very, very early ground cover-y kind of thing, and you need it to have a late, late moment, it’s sort of an interesting combination. I use the Angelica gigas as well for that, kind of to punctuate, because it comes much later as well, but this is even better. So, anyway.
Ken: Well, we’re mentioning water, and I was just going to tell you this too, that, in Northern California in the local papers, they shame homeowners who use too much water. And this garden had its own wells, because they didn’t want to draw on the municipal water supply. Because as I said, it likes a moist place. This place, too, was a hillside, and it was at the bottom of a hill, just like you have.
glyphosate ban headlines continue
Margaret: Yes. Interesting. Speaking of sort of environmental consciousness, you mentioned when we spoke the other day, you mentioned that you’d been reading in the headlines some Roundup news. That’d be the first time I’ve ever said that word out loud on the shows. So, “Roundup with a capital R” news. Yes?
Ken: Well, maybe it was glyphosate news. Just that it’s … I think it’s been banned in 17 countries. I’m not sure of the number, but it was banned I think last week.
Margaret: The chemical was banned in Austria?
Ken: In Austria. I don’t think it’s gone into effect quite yet. Some places have banned it for non-commercial use, some places have banned it except for the use on invasive plants. But it’s happening more and more. And you know Monsanto-slash-Bayer has been sued for a billion dollar or something.
Margaret: Yes. And the Austrian thing I think was breakthrough news because it was the first European Union nation to do this, even though it’s not supposed to take effect until next year. But the EU allows it, so it’s got to be reconciled, those two things. But interesting bit of news to keep track of. So, we should do some questions before we hang up. [Laughter.]
Ken: Well, how’s your garden?
Margaret: Oh, my garden. Let’s just put it this way: Weeding is something where I’m not just bringing a 5-gallon empty nursery pot with me and pulling a few weeds [and putting them in the empty pot]. But between all the moisture we had in spring and now we’ve had a bout of intense heat, and humid, and whatever. It’s really like I’m bringing the tarp and dragging that behind me and filling the tarp. Things are just springing up and reaching their full potential.
So, lots of serious weeding, and re-edging all the beds. The edges get really shaggy once we have heat, especially when we had so much wet. Lots of … It’s almost like another cleanup. It’s like a mini-cleanup for me the way I garden at this time of year. A lot of cutbacks, cutting back Geranium macrorrhizum and other things, so that they’ll look good into the fall. Yes, so creating lots of debris; into the compost heap it all goes.
Ken: I had 30 inches of rain in the first six months of the year.
Margaret: Yes. And normal for our area is just over … or at least low-40s for the whole year.
Margaret: Yes, just for people who are in other areas, it’s for perspective. So, that’s having three-quarters of our rain in the first half of the year.
Ken: Be careful what you wish for, right?
pine needles or wood chips for garden paths?
Margaret: So, we had a question … We had talked about garden paths at one point in the not-too-distant past. And Erik wrote to us to say that he’d welcome some further discussion of paths, in particular if we recommend bringing in or lining paths with materials like pine needles, wood chips, or do we just when we make a path, do we leave the bare soil?
Erik’s in the early stages of garden development and is doing a woodland walk that slopes down away from the house. It’s bare earth right now, but wondering, to sort of define and stabilize it and so forth so there’s no erosion, what would be a good surface for paths? It’s a big subject, I know, but I wondered if you had some immediate thoughts about that?
Ken: A reaction to what you said.
Ken: You said “needles.”
Margaret: Well, Erik said pine needles, chips, he was wondering some possibilities. Yes.
Ken: I just want to say, especially … He puts the word “slope” and “needles” together. Pine needles are very slippery, and on a slope that would be … The gardener and visitors would end up on their butts, I’m afraid.
Margaret: Yes. No, I agree. That’s not … I think pine needles … I don’t remove them from under pine trees ever. That’s where they belong. I think they belong there.
Ken: You know in the South they sell them in bags and boxes?
Margaret: I know. It’s not my thing, but yes.
Ken: Me neither. I don’t always think wood chips are pretty. But if there’s one place for wood chips, it’s on a path, not on the beds, not as mulch with plants. On a path that’s fine. And often it’s inexpensive, sometimes even free.
I know it’s not aesthetically the nicest thing, but that’s a pretty good choice for a path as long as you don’t have flooding like I do when the mulch floats away. [Laughter.]
Margaret: I have a path that has a grade change, an uphill kind of path that’s in a shady area, woodland-y kind of area. And I found that with the bigger chips, they were moving around too much underfoot. But rather than even the small chips, the nuggets or whatever they’re called, I liked the shredded bark.
It’s not a material I love, generally speaking. I wouldn’t want it all over the place. But it kind of packs down in a way, and becomes a nice, thick surface that doesn’t … It’s not so erosion-prone. I don’t ever notice it getting disturbed, like chips kind of float away or move away, like we said about pine needles. So I like that shredded bark.
Ken: And it looks so much more natural.
Margaret: It does. It does.
Ken: It kind of knits—you know how they say things knit?
Margaret: That’s a good word for it. That’s a good word for it, yes. Yes. I saw recently on, I think it was Instagram, Duncan Brine, a gardener not far from … maybe an hour south of where I am in the Northeast, kind of Hudson Valley-ish … He has some gravel paths in a big woodland garden, and someone asked when he posted a picture I think it was, “How do you keep your paths so nice?” And I think that’s the other thing is that, where does everything like to seed in, and all the weeds like to pop up into mulch, and paths, and driveways, and gravel. And he said—and it just made me so happy because that would have been my answer, too.
He said, “Scuffle hoe,” the tool that kind of cuts the head off little baby sprouting weeds, dislodges just a teeny bit of the surface by pushing the tool back and forth. It cuts it in both directions. There’s also stirrup hoes, I use the scuffle hoe [also called a Dutch hoe]. I can show a picture of it with the transcript if people don’t know what it’s like. [Dutch hoe, above, from Garden Tool Company.]
But it’s like, that’s the other thing you have to have if you’re going to do a path network. You don’t want to be crawling around on your half a mile or even 100 feet of path weeding it every two weeks [laughter], like another bed, right? So, maintenance.
Ken: If you don’t have as many tours as you have, grass paths, I think that’s another place where grass might be appropriate.
Margaret: Absolutely. Absolutely. Yes.
Ken: If you do have erosion issues, too, because it’ll hold a little bit. And it doesn’t have to be lawn grass. It can be I suppose clover, and some other things.
black spot and powdery mildew
Margaret: Yes. So, moving on. Of course it’s that time of year, a lot of pest and disease questions. Multiple people wrote to us about black spot on roses, and powdery mildew on various plants.
Sanna, a reader named Sanna said she has several David Austin roses on the East End of Long Island. Every summer they get black spot. She agonizes on how to prevent and treat “the pesky problem.” So, that was one. And lots of others along that vein.
Now, I answered her by email just saying, just as a starter, of course, there’s chemical fungicides, but I am not interested in those, and not going to use them. So, some of the … The thing to always remember with these fungal diseases I think is that it’s not “easy” to prevent them, but it’s easier to prevent them sometimes than cure them organically. Don’t you think? [Wikipedia photo, above.]
Margaret: Yes. So, strict cleanup the fall before, getting rid of nasty tainted leaves and so forth from underneath them. Pruning well, lots of air circulation, all the stuff we hear about over and over again. It really does make a difference. Growing them in the proper amount of sun, which is a lot of sun. Not up against a building, or whatever, not overcrowded. So, I think that’s really important. Have you used any of the organic fungicides or anything?
Ken: I try stuff. Years ago, I used baking soda, and then I tried baking soda with horticultural oil, and it helped. It doesn’t help more than if you open up a shrub and make it vase-shaped, don’t have cross branches. Air circulation is really the key.
But something weird that I noticed and I’m thinking about that now with the rain, I had a rose under an overhang, and it had terrible powdery mildew where the rain didn’t hit it. And where the rain hit it, it didn’t have any.
Margaret: Isn’t that funny?
Ken: So it kind of washes away. So, it’s counterintuitive to think that something wet might be more helpful. Also, powdery mildew, I think that you get it in the spring even though it shows up late in the season. So that’s another thing. Clean up, clean up—black spot, get rid of all those leaves.
Margaret: And so, a lot of the organically rated fungicides, they still have natural chemicals … They have copper, sulfur …
Ken: Copper, sulfur, which are certainly poisonous.
Margaret: Yes. It’s not like nothing. It’s not like spraying it with a garden hose or anything, just to be clear. Some people use Neem oil, but that’s really preventative, not curative once the disease occurs, so that’s another thing.
And again, there’s the “home remedy” of a milk spray to prevent a lot of fungal things. Home brew of water and milk. And that’s all nice again, too, as possibly a preventive and not even necessarily the research doesn’t really support such claims. But it’s certainly not going to erase it. So this is the problem. If we don’t want to use the chemical fungicides, it’s better to put all our efforts into prevention, that really open pruning that you’re talking about, and so forth, as organic gardeners, I think, compared to trying to come up with a curative solution.
Ken: I have to say, I’ve tried a lot of products that are organic, over-the-counter spray things, and I have not seen that they work very well.
Margaret: Right. Lorraine wrote in for instance, she sprayed her phlox with a baking soda mixture that she read about somewhere on a website, not mine or yours. And she didn’t see any improvement, and she wondered why not, and several days of spraying. [Above, American Painted Lady on phlox, from Mt. Cuba Center.]
Again, if the cow’s out of the barn [laughter], it’s like, once you’ve got it, it’s not going to cure it. And the good news about the powdery mildew is it’s not going to kill the plant. It’s just one of those things that, yes, it’s disfiguring temporarily. Yes, good clean up and so forth.
And with peonies, the same kind of thing. We get it sometimes. Virginia wrote in about her peonies getting mildew.
Ken: I think one thing about the phlox is to look for lists of phlox varieties in your area, and nurseries often have them, mailer nurseries, and of course cooperative extension often has lists. Because I think if you choose the right variety, and I do have a breeze coming up the river, but I don’t have any mildew on any of my phlox, and I think it’s because it’s Phlox ‘David,’ which works for me, and a couple of other kinds including some self-sowers from Phlox ‘David,’ which is the white one, and the self-sowers are pink. But I don’t have any mildew on any phlox, which is remarkable. But I think it’s because of the variety, it’s the right variety for where I am.
Margaret: They have resistance. Mt. Cuba Center in Delaware, and also before that even, Chicago Botanic Garden did extensive … have both done extensive research, and they’re published on their websites. I’ll give links to them with the transcript, of Phlox varieties for their regions. There may be that data for other regions of the country as well that we can hunt up, about what you just said: which ones do best, and fight it off the best because of their genetics. So yes, that is an important …
But again, if our gardens are overstuffed, if we’re not pruning along the way, if we’re leaving nasty fading stuff in there, we don’t have good air circulation, it’s just too overstuffed, up against a building as I said before, blah blah blah, it’s going to be tougher to fight that off in a year that supports it weather-wise. [Above, at Ken’s in a semi-shady bed: a pink seedling, white Phlox ‘David’, dark pink ‘Robert Poore’. Read/listen to a whole interview about best phlox for gardens and butterflies.]
a question about ginkgo seedlings
Margaret: So in the last couple minutes, maybe just one super-quick little question, which was a Ginkgo question. It was a funny one. I wanted your two cents on it. Lucy wrote in and said that 60 years ago, she bought through a catalog a Ginkgo. It’s now 70-foot tall tree, and happy in her garden all these years.
But two years ago it began producing seeds, and now suddenly there are seedlings, one to two-year-old seedlings. And she asked a friend, a local plant expert, what to do with them, wanting to share them, and the person said, “Don’t share them, they’re not native. Pull them out and get rid of them.” And that seemed terrible to her. Do you have a point of view about that? [Ginkgo leaf photo in fall color from Wikimedia, by Joe Schneid.]
Ken: Whoa. I have so many questions.
Ken: How come the fruit didn’t smell? And did she have a male and female?
Margaret: All I can tell you is what was in there. She said, “Two years ago, it began producing seeds, which strangely and fortunately don’t smell.” But maybe animals are eating the fleshy part off real quickly before it gets rank?
Ken: I guess there has to be a male in the neighborhood somewhere.
Margaret: Yes. Anyway, so just the idea of what her friend the plant expert was saying, if it’s a non-native tree, we don’t want to plant any more—I mean, I think that’s what’s implicit in the person’s recommendation, is it’s a non-native tree, don’t plant any more of them. That seems extreme.
I know there’s this big tension between native and non-native, and ginkgos support five species of native butterflies and moths, whereas native American … because ginkgo is not an American tree … whereas oaks, native American oaks, support several hundred species of native moths and butterflies. And I know that, but I think as a single specimen tree it’s O.K. to have a ginkgo now and then maybe. I don’t know. I’m sort of there on the fence.
Ken: I completely agree with you. That’s who we are.
Margaret: I don’t think it’s an invasive tree. It’s not rated as invasive.
- [An interview about Ginkgo, an odd and ancient tree, with Peter Crane]
Ken: I don’t know how many seedlings she has going there. I mean, if she’s got dozens, then get the mower. [Laughter.]
Margaret: Right. But to give one to a keen gardening friend to put as a specimen tree in their yard doesn’t seem like the end of the world ecologically, to have one more ginkgo specimen somewhere. Whereas I do definitely support making room for more and more native trees, as I know you do as well, and shrubs, and perennials. Anyway, I just wanted to mention it, and just ask you.
So we frittered away another segment. [Laughter.]
Ken: You’re kidding.
Margaret: No, I’m not kidding. Would I kid you? I’m not going to start lying to you after all these decades, Ken. So, thank you, and get out there and pull some weeds, right?
Ken: Or give up. No, no.
Margaret: No, no. O.K.
Ken: I’ve been weeding. I’ve been weeding. Thank you Margaret.
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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 10th year in March 2019. 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 July 15, 2019 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify or Stitcher (and browse my archive of podcasts here).