overwintering tender plants, and hydrangea issues: q&a with ken druse
WONDER HOW to get ready for the mad stash—just how to prep and then where to put all those tender plants to hopefully make it to next year? Or maybe you wonder about what went wrong with your hydrangeas if they didn’t bloom as well as you hoped this summer. With help from Ken Druse (longtime friend and author of many popular garden books including “Making More Plants” and “The New Shade Garden” and “Natural Companions”), I tackled these Urgent Garden Questions in the latest installment of our ongoing series.
That’s my rex begonia vine up top, Cissus discolor, one of my recent victories in last winter’s experiments in finding the right offseason storage spot for the right plant.
Read along as you listen to the Sept. 24, 2018 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).
begonia boliviensis and eucomis
Q. We’ve have our first taste in the Northeast of fall in some recent days. So I thought it was a good time to sort of talk about bringing things in and getting ready, even if it’s not time urgently yet. We had a question from Amy, who wrote in about her Begonia boliviensis—do you remember those? Have you ever grown those?
A. Yes, I think I’ve killed two of those.
Q. Excellent. Then we’ll be sure to take your expert answers. [Laughter.]
It’s kind of a tuberous begonia thing, and she wrote in and she said it’s been so wet where she gardens this late season and she’s concerned: should she get a jump on it and help it to sort of dry off? She says she lives in Omaha, and does have a nice cool dark basement there, in Zone 5B. The plant was great over the summer, but it’s a wet late summer so far so she’s thinking, maybe better start soon to get it to dormancy out of the rain etc.
And so she’s kind of wondering what’s the best protocol for that plant? I haven’t overwintered one in a couple years, but when ‘Bonfire,’ that first introduction, was the hot plant, maybe five, eight, nine, 10 years ago, I don’t know when it was, I used to do it for a few years. So you have failed or you have done it? Tell the truth.
A. [Laughter.] I love that white one. I guess I failed. I thought it was there, and I watched it, and I kept it cool and dry.
Q. But you tried to keep it growing?
Q. Yes, because what I used to do with it is, and it worked pretty well…. First of all, if it’s wet outside and this is true with a lot of things I think-
A. Well that’s really important.
Q. Don’t you think? Things you want to store you want to dry them down ASAP, right?
A. Especially this year, it’s been so wet. I moved all the things like that, like the Eucomis, the pineapple lilies, they’re all under cover, but where they still are getting light for now.
Q. Right, right. What I do is the same kind of thing. What I would do with that is I used to put it on my back porch, so that it would start to dry down. But it still, as you said, had light because it still had foliage. And then eventually I just put it in my sort of 40-something-degree basement in the dark, dry—pot and all—and I’d remove the foliage as it withered, or if it had withered, and that would be it.
The other key thing was do not water it to wake it up. I waited until I saw these sort of little signs of, almost like eyes, like little eyes starting to swell [below]. Do you know what I mean?
A. After you brought them out? Or inside?
Q. Even inside they would sort of start to wake up. You’d see the beginning, and I don’t know the reason why, what trigger it was reacting to—if it was a change in temperature even in the cellar or what. I would wait or I’d bring them and I’d put them say, in the garage, once it was in the 40s there consistently but still too soon to bring them out. And I’d let the plant tell me it was ready to wake up, I guess is what I’m saying. The same way we see buds swell on other things, even outdoor plants.
A. I actually bring mine out and wake them up.
A. But I’m warmer place than you. I don’t see any little pink points. I just bring them out and start watering them and they wake up right away. Maybe those points are there just little bit under the surface or something. And then I repot them every three years. I check them out.
Q. And I guess the reason that I was saying that, that I let the plant tell me that it’s awake is because if you are in a cold place, and it is still short days—it’s still dark in March, April, and if it’s waking up and you start watering… If you push it too fast or take it out and it starts to wake up in the weak light of late winter and it’s still cold—do you know what I mean? It stretches, it etiolates.
A. Yes, it gets leggy.
A. And pale, and floppy and is never any good. And then when you take it outside it burns.
Q. So I really like, try to keep it quiet and if it absolutely, positively tells me it’s awake, no matter what, then I will give it a drink ,but I try to wait.
A. What are some other—hate to put you on the spot—but what are some other plants like that that you bring in and keep kind of quiet and dormant and then take out again?
Q. Well, it’s hard to get to my cellar in the winter.
Q. My cellar is like a plant supermarket. [Laughter.] Lots of stuff is down there. Well you just said Eucomis, I have pots, cheek-to-jowl, of Eucomis down in the cellar. Is that where you put them? [Pots of Eucomis at Ken’s garden, above.]
A. Yes and if we were in Zone 7 we could just leave them in the ground because they’re close to hardy.
Q. For you. Not for me. I’m a five, Zone 5.
A. No not for me, either. If I was in Zone 7—people in Zone 7 can leave them out. But I love them and I have so many and there’s more and more on the market all the time—or even at the supermarket.
Q. At the supermarket?
A. They’re great plants. Yes, I saw them at the supermarket this week.
Q. Oh, O.K. So Eucomis, the pineapple lilies they’re called because of the sort of shape of the flower head, the inflorescence.
the voodoo lilies
A. How about those nice stinky things?
Q. The nice stinky things?
A. Dracunculus and Sauromatum, or it used to be Typhonium.
Q. The voodoo lilies.
A. Yes. Amorphophallus.
Q. Yes. I have pots and pots and pots of all of those stinkers.
A. [Laughter.] Do you give them their own room?
Q. No it’s funny you mention that, and for people who don’t know these sort of so-called voodoo lilies, a lot of these stink when they bloom because their pollinator is someone like flies or someone who likes the smell of rotting meat. Dead things. Some of them, don’t they call them corpse flowers and stuff?
A. Yes, right.
Q. Yes. Maybe two winters ago, it’s March, I’m upstairs where I work during the days, just above the cellar, and just this terrible smell and I think something died, like a mouse or something, I don’t know. And I open the trapdoor to the basement and I go down the ladder into my crazy, primitive basement, and what it is one of those guys had started to bloom. It had pushed up its spadix, I’m sorry I’m so dopey. [That story.]
A. Both actually.
Q. Yes, its inflorescence and it was oh the smell was horrifying. [Laughter.] What do you do with that in March in the Northeast?
A. You take it to the guest room and close the door. [Laughter.]
Q. Oh, I guess so. But those are easy to overwinter if anyone likes curiosity items like those.
A. Well a lot of people do.
Q. We’re saying that down in the basement we’re putting these bulb-like things that can go dormant that are marginally hardy, they’re not hardy for us but they’re hardy a couple of zones or a zone or two warmer, right?
A. Yes, people force tulips and this is so much easier than forcing a tulip.
A. We just let them sleep and pretty much ignore them and then water them when they show a little bit of growth, and sometimes they flower as you found out.
Q. Yes, a little early. Now when do you, with the Eucomis, with the pineapple lilies… what I found is that is that after about the second or third year, some of them seem to multiply in the pot and the pot’s full and I get lots of foliage and I don’t get any flowers. Do you repot yours on a certain schedule?
A. Yes, pretty much every third year.
A. Sometimes I put them back into the same pot or and take some of the offsets and put them in another pot. But that is repotting, I guess. Just nice fresh medium, and I do feed them when I remember which is not very often. I try to remember to feed them.
Q. And so when you repot them, you repot them in the spring before you go to wake them up. You kind of clean them off, get them outside.
A. When I take them out, right.
Q. O.K. Because I was disappointed by that and I asked our friend Adam at Broken Arrow Nursery, and he said that because they’re of course propagating them—if they see a pot is filled up, they can divide it up and sell a lot of smaller plants next year. Because they’re doing that, they don’t seem to miss a year of bloom, whereas mine were just getting so overcrowded I think. That was his thinking about it.
You do it every third when they wake up. Obviously if it looks really, really, really full, the pot, you could probably do it sooner. I should be doing it sooner if it looks full.
dahlias and cannas
Q. What else—cannas I throw them in the cellar but not in the pots, just in garbage bags that I leave open [above].
A. Oh, and dahlias.
Q. Dahlias, yes, those are a little harder. Cannas are about the easiest thing to overwinter. But dahlias, what do you do with them?
A. Well I leave them out until the frost blackens the foliage and I dig them up with a fork and I don’t break them up until the spring. I just kind of wrap them in newspaper, a couple of layers of newspaper folded over like I’m wrapping a gift with maybe a piece of tape or something.
And then I stack them and the newspaper keeps them from crushing and put them also in the coolest place in the cellar which is about 50 degrees.
I used to do it in dry leaves, because you don’t want them to completely dry. You want them just a little touch moist, and you can moisten them in February–just sprinkle the newspapers or something like that. But I don’t really have access to nice oak leaves that are curled and don’t tamp down and just that would be perfect. A big trash container of oak leaves with your dahlias in it.
Q. Right. I’ve heard people say wood shavings, vermiculite, sand, peat, you mentioned some.
A. I know, we try not to use peat.
Q. I know, but all those types of things and about 40 to 50 degrees. Yes, I don’t grow so many and the ones I have grown I’ve sometimes saved them over but not so much.
more details on overwintering bulblike plants
arisaemas, or jack-in-the-pulpits
Q. Arisaemas, don’t you have some? Did we mention those?
A. Those are hardy because you were talking about things that aren’t hardy for us, but I have a lot of Arisaema, which are Jack-in-the-pulpits. There are two North American species and some people say there’s 250 Asian species, and I probably have about five or six.
I used to plant them in the ground. I still do, and sometimes I would lose them. But I was actually in Vermont, and I saw someone growing them in containers and I thought, well that’s interesting. That person was overwintering them in a closet. Not even cold. Just dry. And I started potting them and overwintering them in the basement just like we were talking about the Eucomis. And then I bring them out in May and water them and it’s fantastic and I haven’t lost any. And I do repot them about every second or third year.
Q. The reason I ask is because I bought… I was so attracted to these pots at the garden center of Arisaema rigens, which gets to be a big one. Oh my goodness. And it has these beautiful glossy leaves. It’s just so handsome. And that Jack thing is purple and whatever, the Jack-in-the-pulpit part. [Above, A. ringens photo by Ken Druse.]
The person told me that just be careful because—you said you lost some of them—that the squirrels and stuff love to dig these even though these are not native plants exactly. That they dig them up and it’s like hide and go seek with these particular Arisaema bulbs. I don’t know if they’re bulbs or corms or tubers.
Q. Tubers, yes. And so that’s what I figured had been happening in the past when I tried so now I’m going to do these in pots. I think I can do them in pots just like what you said, yes?
A. Oh, absolutely.
Q. Yes, so I have them and they’re going to go in the cellar.
A. They’re really big. They can become incredibly big, and in a pot they probably won’t. How many do you have? You have more than two?
Q. I have two. [Laughter.]
A. Oh. I was going to say if you have three, try one outside with manure and everything.
Q. True. Maybe I’ll do that anyway. Yes. Maybe I’ll do that anyway.
- more about unusual aroids to grow and overwinter, with Tony Avent
bananas, musella, a camellia and shell ginger
Q. Have you tried any new experiments beside your usual suspects that you overwinter? I mean I put a lot of things in the garage, which is totally unheated and I’m in a cold zone—like things that are hardier, about hardy, trees and shrubs [including potted Japanese maples].
A. Because of space and I’ve done it in the past with bananas, cutting the bananas back and I always think, oh well, that’s never going to make it and I did it with a Musella. I don’t know if you know what that is.
A. It’s like a dwarf banana. It doesn’t have edible fruit. It has a completely different flower structure, and I did that in the fall last year and brought it out in the spring and it is blooming. It’s been blooming since May, end of May. It’s still blooming now. It has this amazing yellow flower and so that’s how you do that.
This year I did it with a camellia, because I had a camellia that is just too big and it really wasn’t looking too good and I thought, I wonder if I can store that dormant in the dark in the basement?
Q. You’re kidding me.
A. And I did.
Q. And then what happened? And then you just took it out in March or April or something? When did you take it out?
A. Yes, I would say late April.
Q. And so you checked it just to make sure it didn’t dry out completely, completely in the late winter?
A. I said, “Keep sleeping, keep sleeping…”
Q. Keep sleeping. Yes, you read it some bedtime stories. [Laughter.]
A. “…because there’s no room for you upstairs.”
Q. Interesting. Well and it is this constant experiment—even if you’ve been doing it for a long time, it’s this constant kind of experiment, and if you’ve had a lot of plants… I call these “investment plants” as do many people. Because frankly economically there’s an incentive to try to figure out the needs of a particular plant, because you might buy a little something, a little one of something.
Like I bought this thing called shell ginger, variegated shell ginger, Alpinia zerumbet, whatever. It’s green and yellow, and it was like so gorgeous I had to have it. It kind of looked like a canna in the pot maybe, but with very showy leaves. But it was like $29.95.
Q. …and that’s was in maybe a 2-gallon pot; it wasn’t too big. But it was so attractive I just had to try it. And so I wasn’t going to compost that thing and now, don’t you know, three, four years later, because I figured out what to do with it, it fills a 36-inch bowl—a big, low terracotta bowl that I have by my patio. It fills it; it’s massive.
It’s like a shrub now, and what I figured out is that I looked up its history: Where did it come from? What did it do? What was the temperature like where it came from? And I found a place that was a little bit of light and 40ish, 42, no more than 45 degrees, in this shed I have with a skylight, and a little bit of heat in there. So it’s not freezing. And I every so often go out and give it a little bit of water so it doesn’t desiccate, and it was sort of half-awake, half-asleep all the time. And wow. So now I have this plant that if I could even replace it would cost $200. Do you know what I mean?
A. Do you trim it back at all? Or do you have to clean it up in the spring?
Q. Yes. When it comes out, it’s a little ratty. Some of the old foliage is ratty, but there’s lots of new excitement coming from the crown down below and I’ve seen pictures where it maybe could have these ginger-like flowers. So maybe I’ll get that eventually.
Sometimes you just have to try. I failed with that rex begonia vine (Cissus discolor) a number of years and then I found that my mudroom, which is maybe 55 degrees, 50 degrees and bright, it worked in there, the rex begonia vine. And then you have to cut it back hard.
It’s hard to cut back a 6-foot vine in late winter because you grew it that tall, and you loved it.
A. It is so hard to grow that plant, and it’s so beautiful. There’s no person who can walk by that plant without stopping. It’s so beautiful.
Q. It’s fabulous. It’s fabulous. So I now I’ve figured it out. Again, it’s like it’s this experiment. You have to experiment and kill it in a few different places in your house or garage or whatever.
overwintering figs, rosemary, citrus
ON THE SHOW, I promised that with the transcript I’d give links to past interviews on how to overwinter figs and the rosemary and other popular edible plants that confound people:
hydrangea questions, and a dead buddleia
Q. So maybe we should just do a couple of quickies–quickie questions about other things besides where to stash what.
A. I forgot, are we just talking to each other?
Q. Oh, there’s nobody here is there? [Laughter.]
At a recent Open Day event at my garden, somebody asked me—actually more than one person said, “Why are your Hydrangea paniculata so big?” They were referring to the panicle hydrangeas that were blooming. The answer is not fertilizer. You know what the answer is, right?
A. Well, it depends on the variety.
A. Yes, and people can cut them back. Maybe they’re cutting back, too. It’s mostly that there are varieties like ‘Little Lamb’ and ‘Limelight,’ which are kind of small [approximately 6-8 feet]. But ‘Tardiva,’ oh my gosh, stand back.
Q. It can be 12 or even 15 feet, right?
A. Yes, sure.
Q. 12 to 15 feet for me, and also straight H. paniculata is big.
A. 10 feet wide.
Q. And mine is. With those Hydrangea paniculata, make sure you really read—even though they all may look kind of small at the time that you buy them in the store—read what the eventual size is. Your pruning can make a ‘Tardiva’ 8 or 10 feet instead 12 feet, but it’s not going to make it 3 feet permanently. And a ‘Little Lamb’ isn’t going to get to be 15 feet, right? [A comparison of just 14 of the many paniculata cultivars, as an example.]
A. Probably not. But there’s so many new ones, and sometimes you don’t really know. You’ll read a tag and these plants are so new it may not be right. But anyway. You can prune it.
Q. So pruning method—and variety is super-important. Another hydrangea question from Inez, Zone 6A Dutchess County, New York:
She says that her ‘Endless Summer’ hydrangeas—good name [laughter]—weren’t blooming. She also lost five Buddleia in the garden during the same time. But ‘Endless Summer’ hydrangeas not blooming: In the time we have left, what do you think?
A. ‘Endless Summer,’ like macrophylla, like mop top hydrangeas.
Q. The blue guys.
A. Except they bloom on old wood and they bloom on new wood. They bloom twice in the season and after a very cold winter like we had last year, the buds for the spring blooming could be damaged. Maybe she asked you before—and it’s blooming maybe now, the second set, or maybe in August. We had such a cool and long and wet season this year that maybe they’re blooming right now and she’s hitting herself in the head for asking the question.
But I would say the other things is if they’re congested, or if it’s a little shady. You really have to remove the three-year-old growth after it blooms. You can tell if you look at the plant, the canes or the stems that come up from the ground, the ones that are pale, tan and kind of woody and brittle—cut them out.
Q. At the base.
A. Don’t prune the whole thing. If you prune the whole thing with those kinds of hydrangeas you don’t get anything. You can’t shear it or shape it. You have to thin it. And you remove about one-third of the growth every year. You remove the oldest growth, because it won’t really bloom again. You want that nice fresh growth. So there’s lots of reasons. Could be too shady. Could be that she pruned it. Could be that it was a very cold winter.
Q. And you lost the spring ones, right.
Q. And what do you think about five dead Buddleia.
A. Sounds like the same thing. Sounds like it was kind of a cold winter. Dead? Lost?
Q. And what I wonder is because here where I am, they die to the ground—Buddleia davidii, is that right? The sort of common butterfly bush, they would die to the ground. I have to cut them down just as they start to push new growth from the base. I cut them down to a few inches, so they’re not really dead even though the plant above-ground looks dead. I think a lot of times people don’t know that and they think it’s dead.
A. You think maybe she dug them out or something?
Q. I don’t know. I’m just saying they do look dead, the upper parts.
A. If you’re in a cold climate like you are, they act as if they’re herbaceous perennials. They die to the ground. It doesn’t mean that they’re completely dead or gone. They usually do push up new growth.
Q. Right. So I like to take the whole top off, even if it’s 6 feet tall, take the whole thing. I don’t have them anymore.
A. You mean the twiggy, dry stuff?
Q. Exactly, exactly. Yes, cut it down.
Are you putting anything on your back porch yet to start to dry it down for storage?
A. Well I’ve put stuff under an overhang and everything is so wet and the pots are so heavy.
A. And it rained 21 inches in the month of August this year. In one month.
Q. In your area of New Jersey? Maybe we got 12 or 15. I don’t know how many we got. It’s crazy. Wow.
A. At least it wasn’t all at once. It just was continuous so the pots have never dried out and that’s why I’m looking at the sun right now and thinking, “What is that?”
Q. Well go get your …
A. Will I actually be able to mow the 12-inch grass?
Q. Well go get your handcart and drag some more stuff under cover, and I’ll talk to you soon.
more expert advice on overwintering
- Dennis Schrader of Landcraft on general mad-stash advice, plus many special foliage plants from coleus to Phormium, Acalypha and more
- Kathy Tracey of Avant Gardens on tender succulents (and more collector plants, including Abutilon and others)
- From bringing in the houseplants to stashing the Brugmansia (above) and everything else, a roundup of tactics
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 ninth year in March 2018. 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 Sept. 24, 2018 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).