when variegation reverts, killing goutweed, cucumber wilt, black knot fungus: q&a with ken druse
IS IT TIME to take in the houseplants? That’s just one of the things I compared notes with Ken Druse on during the September session of our monthly Urgent Garden Question feature. Among the other topics we covered: Why do variegated plants sometimes revert to all green? How can we tackle insidious weeds like goutweed? What causes cucumber vines to get crispy and collapse, and what about those black swollen galls on some fruit-tree branches known as black knot fungus?
Ken, an award-winning garden photographer and author of more books than I can count, including “The New Shade Garden” and “Making More Plants,” produced his own “Real Dirt” podcast for 10 years, all available on KenDruse dot com (and still available on iTunes, too).
Read along as you listen to the Sept. 4, 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). Want to just browse past Q&A shows with Ken and me? They’re at this link.
the september urgent garden question q&a
when to take in the houseplants?
Q. So I’ll get right to the point: I’m thinking about those houseplants, because I’ve had nights in the high 40s most of the last week, and 40 or 41F is forecast tomorrow. I’m like, “I don’t want to do this.” Have you done yours yet?
Ken. Have I done mine yet? [Laughter.] They say you’re supposed to bring your houseplants in when the indoor temperature is the same as they outdoor temperature. Well, that passed—I think the heat went on once. They say you’re supposed to bring them in before the heat goes on inside, and every year I think, “I’m gonna do it; I’m gonna do it by September 15.”
And then I find myself throwing a bed sheet over the indoor plants because the frost warning has come.
Q. You have that bed sheet too, huh? That special bed sheet—I have one in my mudroom closet [Laughter.]
Q. The ideal thing would be to like stage them, move them not from outside to inside but first put them maybe under the overhang of your porch, or in your garage a little while. To let them go slowly into the drier indoor environment.
Ken. And that’s better anyway because when you bring them inside you can arrange them, instead of, “Oh my gosh, oh my gosh.”
Q. [Laughter.] Incoming!
Ken. And then you’d also get a chance to examine them, and make sure you’re not bringing any hitchhikers in.
Q. Oh, dear.
A. I try to keep them off the ground because the worms—oh, worms!—get into the pots and that’s the worst thing.
Q. I know.
Ken. If you think there’s something like that in your pot, what I do is I’ll put the pot into a bucket of water for half a day or something. It overwaters it, but that will drive away a lot of things. Then leave sit out on the porch for a couple of days. This year I swear, I’m going to do it on time—which means soon, very soon.
Q. I know where you’ll be tonight. [Laughter.]
Ken. And there’s another thing: to not repot them.
Q. I think spring for that; I don’t want to do that now.
Ken. Unless it’s a plant that dries out like almost every day and you have no choice. Otherwise try to wait. And don’t feed them until March.
Q. No, no, no.
Ken. You know, one of the popular houseplant potting mixes has fertilizer in it—I won’t mention names.
Q. No names, please.
Ken. And it burns them, or forces growth when they’re trying to sleep. It can kill them.
Q. So we’ve both answered the question: No, we haven’t done it with our houseplants, but we’re thinking about it.
why do some variegated plants turn green?
Q. I have a question from Lucinda on Facebook, who asks:
“What should be a gardener’s approach when a variegated cultivar starts to lose its variegation?” She specifically noticed this with some of her variegated hostas [above], and then, “the variegated Brunnera I loved, also became all green.”
Should she prune away those non-variegated leaves, or is this happening at a more fundamental level. Is there any hope?
Ken. I grow a lot of Brunnera because it’s one of the best plants for dry shade, and we’re always looking for something for dry shade.
Ken. But I’ll get some kind of fancy one like ‘Looking Glass’ or ‘Jack Frost’ or there’s a new one out called ‘Alexander’s Great’ that’s just beautiful. Some of them are so silvery and a lot of them have silver splashes on the leaves. And I find that after a very short time—a couple of years—that they all look alike.
Ken. They’re mostly green, and have a little bit of silver. I think what it is that they’re not really reverting but they are self-sowing.
Ken. They’re having a little bit of naughtiness, and new plants come up, and they look like they are just where the old plant was. And especially the really fancy ones don’t seem to stick around.
Q. I’ve read that from like ‘Jack Frost’ forward—the newer cultivars—that they are supposed to be more reliably stable. Some of the earlier ones were not. But then there’s the question that you just brought up of seedlings. Sometimes the plant you bought was propagated by tissue culture, and should be identical to its hopefully stable parent, yes? But if it was a seedling it might not be so stable.
Ken. I think if I got a fancy one this time, I would grow it away from the other ones, in isolation in a place where I can keep my eye on it.
Q. Oh, poor lonely Brunnera!
For me they’re so wonderful and durable and do what I need them to do, so it’s OK.
Q. I’m going to look up ‘Looking Glass’ and ‘Alexander’s Great’ because I don’t know those and I’m not a big Brunnera grower, but maybe I will be. So what’s next on our list to tackle? [Above, left to right: Photos of ‘Looking Glass’ and ‘Alexander’s Great’ from plant breeder and wholesaler Terra Nova Nursery.]
step 1: how to identify pests and weeds
Ken. We’re talking about things people have asked you, so I’m going to put you on the spot. What’s the most often-asked questions besides about tomatoes?
Q. And besides, “Why didn’t my hydrangea bloom after I pruned it?” [Laughter.]
Ken. Oh, I just got that this week.
Q. I know; endless. But that’s OK, because it’s a good question. It’s interesting that you ask, because I was just thinking about this the other day, how a lot of the questions I get are “ready, shoot, aim” kinds of things—where someone says, “I have this, and I am doing this about it.” But what the first “this” is, is a misidentification of the pest or the weed—jumping to conclusions.
They’re looking to me to affirm it, or offer an alternate thing to do, but they already have diagnosed it and that’s where they’ve gone wrong.
An example the other day came from someone named Pat, and she said that the leaves and flowers on two kinds of her Clematis “have been eaten in their entirety by fireflies,” and this happens around August.
Ken. Wow, that’s unique.
Q. And I said to myself, “Margaret…”
Q. I knew that our common Eastern firefly [Photinus pyralis]—I knew she was in the East, too—is carnivorous, so it doesn’t eat plants, right? And so I thought: here’s another example of assuming something because it kind of looks like something you have seen before.
I had another one the other day that was the wild cucumber vine with the frothy white flowers, and not fleece flower or fleece vine—you know what I mean. Things that sort of look alike but they are not the same, and if you want to tackle one or the other it might be a different tactic.
So I said to Pat that I think it’s a blister beetle, and in fact there is a Clematis blister beetle and it behaves in the way she was describing. It’s a similar-looking thing, and how did I figure that out? Because I have Arthur Evans’s field guide to beetles because I’m a field-guide freak. With all my field guides, I can look up any kind of bug, and I love doing that. What about you? What do you use when you’re trying to suss out what something is?
- about blister beetles, from Univ. of Florida
- The Clematis blister beetle on BugGuide
- Clematis blister beetle on Extension.org
Ken. Talking about that I also thought about something else that people do, about the “ready, shoot…” They think, “If one-third of this chemical…”
Q. Don’t say it!
Ken. “…in the water is OK, then three times as much will be three times as good.”
Q. Will kill it really dead.
Ken. We won’t have to get into that right now.
I find myself in spring, looking at things that are like 6 inches tall and I think, “Is that a plant?” By that I mean is it something I want? It’s right next to something I planted. “Is this something I planted? Is it a weed?”
I’ve been doing this for a really long time, and unless it’s something that I recognize and it turns out to be lettuce or something, some wild lettuce, I’m going to take my field guide out with me, “Weeds of the Northeast.” I don’t know if there are ones for other parts of the country, but a wonderful thing about this book is that it shows you the seedlings when they come up.
Q. I forget his name who wrote that; who the author is.
Ken. Richard Uva, Richard Neal—several people.
Q. That’s been around a long time, and it’s still in the bookstore near me; it still sells that one. If people want to go wider, throughout all of North America, maybe two years ago came “The Weeds of North America.” The authors are Dickinson and Royer, from the University of Chicago Press, and that also has all the seedlings but is in a wider geographic area.
And I think that’s a great point, because a lot of times out tactical approach should start with getting rid of the right seedlings before they are 7 feet tall. [Laughter.]
And with bugs, by the way, I’ll always mention every show that I love BugGuide.net for keying out bugs, and they’ll also help you. So invest in some field guides, I think.
- Interview with the author of “The Weeds of North America”
- Margaret’s favorite field guides
- Weed-ID websites Margaret uses
how to get rid of goutweed
Q. I have another listener question for you, Ken, from someone who wrote:
“I want you to know that I almost hung up my trowel in frustration after years of battling the invasive, pervasive, sneaking, impervious to my tweaking goutweed (Aegopodium podagraria).” She wonders if we have any tactical advice besides go hide under the bed with a box of cookies. [Laughter.] Which could be one of the ways to deal with it.
Have you tackled it?
Ken. Yes, a little bit of variegated goutweed [above], which isn’t as bad as the solid green, hitchhiked into the garden with another plant from somewhere. Oh my gosh. You can still buy it in the nurseries if you’re insane, and that along with chameleon plant [Houttuynia cordata]…
Ken. …are two things I think should be banned everywhere.
Q. Did you say that word: chameleon plant? I have a war to do this weekend; it’s horrible.
Ken. I have a friend who had goutweed, and she tried to get rid of it for many years, and she said, “I’m going to will it to my grandchildren, because it will outlive me.” And she finally moved.
Ken. Extreme. It’s a deciduous groundcover, and don’t ever fall for it.
Q. It’s rhizomatous. Its underground structure is very tenacious, so if you just yank it out, it may be gone above the surface but underneath lurk tiny pieces of rhizome that would sprout more plants, right?
Ken. Any little piece is going to come up. And there is very little you can do. You can try digging it out, and we talked about how it breaks off and keeps coming up again. So like every three weeks dig out that variegated one.
As far as that solid green one, if it was planted in an area as a groundcover that you can really handle, herbicide won’t work. I don’t know of any herbicide that will work. But I think that maybe solarization might help, if you want to explain to people what that is.
Q. It’s harnessing the power of the sun, with the device that you use to do that being a piece of black plastic. I love the heavier stuff that I don’t have to throw away after one year; I have some sheets that I have used for many years of the thick plastic, the thicker-mil stuff.
You’ve got to put it on early. You can’t put it on this time of year, at the beginning of September for two weeks, and figure it’s a little sunny out so it killed the stuff. Unh-uh. You really want it to be there for goutweed…
Ken. For the whole summer.
Q. …and maybe next year, too. And some people say to let it sprout, mow or cut it down—so in other words, it’s used some of its energy already to push up from its resources in the roots. Let it do that, then cut it off so you’ve weakened it a little bit, and put the black plastic on so that it’s trying to push the next time under the black plastic in the heat. Now this assumes a sunny situation, which isn’t always the case—I’ve often seen it in the shade. [Note: In shade, you’re not really solarizing as much as depriving the plants beneath the sheeting of light and therefore of the ability to conduct photosynthesis.]
Ken. And if it’s in a bed, good luck.
Q. And that’s a good point, Ken. If you have—and I have that other thing you named that I won’t repeat the name of, grrrrr, the chameleon plant [above]—and that’s gotten into other things. I thought I had it set back, but I didn’t.
So if I want to rescue the other things before I attack this bed the way we were just talking about, I’m going to have to take them out, bare root them, wash their roots. I can’t just dig them up and plant them with soil on them, because I am going to move the invader, too.
Q. So that’s tricky; a tricky thing to do. A lot of people recommend using herbicide as part of the regimen with this damn thing, too—digging, digging, digging, solarizing—in other words attacking it on all levels. I don’t know; I’ve never done that.
Ken. Or move.
Q. You’re going to keep suggesting the moving, are you?
Ken. Well after hearing what you are going to do to it, this is a new career. [Laughter.]
Q. What’s your worst weed—do you have chameleon plant, Houttuynia?
Ken. There was a little chameleon plant when I came to this garden 22 years ago. It was here, and it still is. I’ve done everything I could possibly think of. Well, I’ve give up; I’ve stopped—now I just keep an eye on it and get rid of it when I can, but I don’t see any stopping to it. You can eat it as well, but I haven’t.
Q. I know, and it’s a Chinese herbal medicine kind of thing, and it’s eaten fresh like a green—like a watercress-y thing. But oh it’s a stinky thing, and it’s my worst weed as well. And then I have some woody weeds, like Oriental bittersweet.
Ken. We’ve talked about that before—bittersweet, wow, up the trees. But stiltgrass still is the monster here. And you know I should mention, too: I sometimes have garlic mustard [above], which people say is their worst monster, and I find it very easy to pull. If I haven’t had time and pulled it all, I’ll go around when it starts to flower and cut the flowers off with scissors.
And that’s another thing with the Aegopodium, the goutweed, that you can add to that list of things to do: not to let it go to seed. You’ve go the underground rhizome, the seeds on the top—maybe if you just move your house on top of it.
Q. I think what we’re saying—and we’re being a little bit flip, talking about moving and it being hopeless—but you need tenacity. With any of these, especially rhizomatous tough weeds, we have to be even tougher. It’s going to require a long commitment, realistic expectations and probably multiple tactics. Like I said, if you’re going to put the plastic over, first cut its head off—weaken it, weaken it, weaken it, weaken it, weaken it. Multiple layers; it’s a war.
cucumber vines get dry and collapse
Ken. We got a cucumber question—and I know you are the edible person.
Q. I like a good cucumber in my salad—I like Greek salad. Is that what the question was about, my Greek salad recipe?
Ken. Sheep versus goat is the question.
Q. I like sheep, OK. [Laughter.]
Ken. We got this question from Sharon in New York State:
“This summer we grew ‘Straight Eight’ cucumbers, and they were looking gorgeous—lots of vines, blossoms, and vegetables.”
Fruits, I’d say, but I don’t want to correct her….
Ken. …“We arched a metal wire fence over the raised bed with some twine suspended so the plants could grow up onto the fencing. It was all working according to plan, except the other morning virtually the entire bed had dry brown leaves, with curling edges. We don’t think they’re going to produce any additional cucumbers.”
Q. It’s funny, my neighbor just came over and told me the same thing, last week. She was like, “What’s wrong, what’s wrong?”
When I see that and I didn’t see powdery mildew gradually infest the plant and cause the leaves to decline—kind of an obvious coating on the leaves earlier—I’m betting it’s a bacterial wilt, and that’s spread by cucumber beetles. And you don’t have to have 10 million cucumber beetles, in my experience, to have this.
The adults overwinter, and I believe in their digestive tract they have the bacterium and wake up next year and spread that more—I think that’s how it works. As I told my neighbor, Missouri Botanical Garden has a great website and a wonderful factsheet about wilt in cucumbers.
an aside on panicle hydrangeas
Ken. I think we should think about something a little more cheerful. I don’t mean to change the subject on you, but I’m in love with an old friend.
Ken. You know, I’ve taken these plants for granted, but this year—especially at this time of year when everything else is asleep—the Hydrangea paniculata are incredible. They’re fragrant, and the bees love them. I think I’ve got 10 different ones, and all over the area they’re just beautiful. And they’re so easy, and you can cut them back and they’ll bloom. Maybe you have to run over them to hurt them.
Q. No, run over the goutweed, Ken, not the hydrangeas. They’re wonderful, and I really like the big ones. Last week on the show I was talking to Dan Hinkley, and we were talking about new hydrangeas and ones he loves. And paniculatas—how we both love the big ones that are more like the species, not the little ones being introduced. Yes, they freshen up the garden late in the season.
Ken. The earliest one here is ‘Brussels Lace,’ which is almost finished, and then ‘Tardiva,’ is just coming now.
Q. I love ‘Tardiva,’ it’s a big, beautiful one.
black knot fungus on stone fruit trees
Q. We have 2 more minutes so we can probably do Lenny’s question. He says:
“I’ve got several stone fruit trees (plums and peaches) that are afflicted by black knot fungus. Ever encounter this? Any ideas?” [Photo by Robert L. Anderson, USDA Forest Service, Bugwood.org.]
I haven’t had it in my garden, but all the wild cherries around me in the woodland around me get it. It almost looks like stretched-out tubes of charcoal around the twigs. It’s fungal.
Apparently attempting any control is a combination of tactics that starts with pruning out and burning or otherwise destroying the twigs with the knots on them—don’t put them in the compost. We have to do that before bud break in spring, because it’s in the moist spring weather that the spores—or maybe they’re technically something like spores, I don’t know [updated note: they are called ascospores]—will move around and spread to new wood, to young twigs.
Most people also probably use a fungicide, and there are fungicides approved for organic use, like lime sulfur. I don’t know about you, Ken, but I don’t do any spraying myself, even if it’s an organic spray. I ask a tree company that practices IPM to come in and do the spraying. I don’t have the gear to do that properly on a large tree.
Ken. A neighbor of mine has that on I think a plum tree, and I can’t even see the bark any more—it’s all knots.
Q. All that’s got to come out. It’s the worst on plums and prunes, and it gets on cherries—and the wild cherries it’s worse on than the cultivated ones. It’s least damaging, I think, on the peaches, ugly but less damaging.
Phew! That’s a lot of questions for one show, Ken.
Ken. We did good.
- More on black knot: If wild trees around you have it–and you are downwind of them–that will make it a tougher battle. Cornell has a good short explanation of the life cycle of the organism; Ohio State goes into more detail. University of Maine Extension compares the different fungicides (safer and less so).
calling all questions for next month, a theme show on overwintering strategies
A PREVIEW: For October’s show, we’re going to tackle the “mad stash” in a themed edition: how to overwinter tender things I call investment plants, from cannas to bananas and who knows what, and keep those houseplants happy, and maybe even where the heck to store all those potatoes or carrots you’re digging, too. Tell us what you’re hoping to successfully overwinter (or store for later eating) in the comments below.
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 Sept. 4, 2017 show right here. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).
(Purchases from Amazon affiliate links yield a small commission.)