TODAY WE’RE going to do some multiplication, as in: make more shrubs, thanks to a lesson in propagating favorites like Hydrangea or elderberry or Physocarpus and more, courtesy of our friend and regular guest, Ken Druse. Ready to learn the basics of shrub propagation and have plants to share or to repeat in your own garden?
You all know my old friend, Ken Druse, author of 20 garden books. So rather than repeat the rest of his bio, I’ll share some news: Ken’s being honored the evening of June 17th, 2021 by Rutgers Gardens, the botanical garden of Rutgers University in New Jersey.
Of course I would not miss that virtual event (ticket information is here). The celebratory evening includes a video tour of his garden at peak bloom, and also a live Q&A session.
Read along as you listen to the June 14, 2021 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on Apple Podcasts (iTunes) or Spotify or Stitcher (and browse my archive of podcasts here).
Plus: We’ll have a book giveaway of Ken’s “Making More Plants” (affiliate link). Enter by commenting in the box near the bottom of the page.
taking softwood cuttings with ken druse
Margaret Roach: Hi, Ken, and congratulations on the honor from Rutgers.
Ken Druse: Thank you so much. You surprised me, Margaret.
Margaret: What? You didn’t think I noticed that you were being honored?
Ken: I didn’t think I remembered.
Margaret: Oh. Well, you better show up, hon.
Ken: I know. I know.
Margaret: Yeah. I’m really excited for the tour part. That’s going to be great. Usually I see still images that you share with me, but I think it’s going to be great.
Ken: No, it’s a video. We haven’t talked about it much, but I was in the hospital, so it was a few days after I came out of the hospital, so I’m pointing at things with a cane. It’ll be interesting to see what happens. [Laughter.] But I made it through the garden, so we’ve got a video tour.
Margaret: Good. And you’re going to do Q&A. Good. Good. Good.
Margaret: All right.
Ken: I’m so thrilled that people are listening to the podcast and reading the transcripts when we get together. You really have a lot of people. It’s great.
Margaret: Yeah, it’s getting to be more and more. I think the “New York Times” columns have helped in that and a little bit because people look and they read those, and then they see the link and so forth, and they see that I have a podcast. So that’s great.
So speaking of that, you’re the author of “Making More Plants,” one of my favorites of your books. And we’re going to make some more shrubs. But in a recent Times column a couple of weeks ago, I did that one about making more houseplants, because I had read on Instagram as I think you and I talked about offline, about the guy @houseplantjournal, Darryl Cheng, how he had used a recycled bento box from his Japanese takeout to propagate some houseplants that needed… [Laughter.] Especially fancy-leaf begonias, and he put some leaf cuttings in them on moss and kept them in their sort of percolating in the humidity.
Anyway, did you have to do that with any of your… Did you sort of rehab any of your houseplants on the way out the door? That’s what we talked about last time you were on the show.
Ken: Yes. I think now, at this time of year, I turn my attention to… Now, you said shrubs, but it’s really, as you know, the deciduous flowering shrubs, or deciduous woody plants.
Margaret: So it be a tree technically or a shrub?
Ken: It could be a tree, but generally it’s a shrub. But the reason I’m saying deciduous, it’s not an evergreen. It’s not like a conifer, a needle-leaf evergreen. It’s something that drops its leaves in the winter. That’s what we’re talking about.
Margaret: Yes. And I’ll confess, besides the occasional begonia leaf [laughter], I’ll confess the only thing I’ve propagated this year, or even easier ones like twig willows that I sometimes cut off some at the beginning of the season and stick it in the ground, in my vegetable garden and keep it moist, and those will root practically anywhere. But I don’t know about… I haven’t done what you’re going to teach us about.
When I look up propagating shrubs or trees, woody plants by softwood cuttings, I get a lot of different lists of what will work, whatever. So tell us, what do you think some good candidates are?
Ken: Oh, you started a good list. hydrangea, elderberry, Deutzia, Weigela, shrub dogwood, Viburnum, surprisingly, even the early spring viburnum, Forsythia, rose of sharon, fringetree. There’s a lot.
Margaret: Right. Right. And, and some lists like I’ve seen lists from the Royal Horticultural Society and from University of California and other kinds of places and places that, for professional propagators, where they have a fancy propagation house with a mist bench and heated this and humidity control and antifungal, blah, blah control [laughter]. Those lists might be much, much longer, but these are some tried-and-trues for you, right?
Margaret: Good. Good, good. O.K. So where in the world do we begin? And this is the time, right?
Ken: This is the time. Softwood cuttings can be taken from late spring to early summer. So we’re talking about right now. And softwood is the term we use to describe green parts of a stem that are neither too young or too old, neither at the growing tip or in the stiff woody parts closer to the base of the plant. I think of it like Goldilocks. It’s not too soft or too hard [laughter]. The growth has to be just right.
And you can judge the length or age of a stem for a softwood cutting by bending it. And if it snaps with a clean break, that’s the place [above].
If a stem bends and just gets round without snapping, it’s too young [just above]. If the cutting bends like an elbow, creases without breaking, then that’s too close to the brown, woody older part of the stem, and too mature, because you want just the right age [below]. If it’s too young, it’ll rot, and if it’s too old, it won’t root in the same way.
Margaret: Sounds like asparagus [laughter]. You snap the ends off and it doesn’t… Do you know what I mean?
Ken: Yes, I do.
Margaret: Yeah. It sounds like the snap test is like that.
Ken: If you wanted to test, I’d say if you have a coleus, that’s a good plant to test on. Because it’ll really be round at the tip and it’ll really snap in the right place. And then that tells you. And usually those cuttings are… Well, one thing, it shouldn’t be flowering. And if it is flowering, remove the flowers because when something’s flowering, it’s mature, it wants to make a seed, it doesn’t want to make roots, and we want roots.
And if all that bending and creasing mangles the stem too much, you’ll learn from that how big the cuttings should be, and then you can go to another stem on the same plant and cut it there. Usually the cuttings are 2 to 4 inches long and have three to four developed leaves or pairs of leaves.
Margaret: O.K. So it’s short but… And obviously the space between leaves varies by species. So some, to get two to four pairs, we’d have to have longer than a 2- or 3- or 4-inch cutting maybe, but that’s the basic guideline, yes?
Ken: Mm-hmm. That’s general, but this is specific: Collect the cuttings early in the day when they are full of moisture.
Margaret: Makes sense.
Ken: And soft plants lose moisture rapidly, so don’t let them wilt. I carry a bucket of water with me when I’m gathering cuttings, but you can also have a flat with moist paper towel and lay the cuttings down and cover them with the moist paper towel. And don’t keep it in the sun. Keep it out of the sun. Make more sense?
You can also put them in a plastic bag. When I’m traveling, if I’m in California or something, and I take cuttings that I’m not going to be able to process till I get home, I’ll put that bag with the cuttings in the refrigerator. And I’ve done that with coleus and begonia. And at 40 degrees in the refrigerator, they stay perfect for rooting.
Margaret: O.K. those not being shrubs of course, or woody plants?
Ken: Right. But with woody plants, too. I just thought of that because it’s crazy to think of something so tropical being able to tolerate that. But that works.
Now you must have a place for rooting the cuttings. And every spring, almost every spring, I like to make what’s called a sweatbox [below, under construction]. Have you ever heard that term?
Margaret: I have. It makes me laugh. It sounds like something at a gym or something, like the sauna or something [laughter].
Ken: Well, that would be good. But it’s a shallow flat with drainage holes filled with immaculately clean medium. For example, very coarse sand or vermiculite or fresh potting soil. And I like to use perlite, because it’s really, really clean when white perlite comes out of the bag.
So I moisten the perlite, and I tamp it down in the flat with something like a fresh, clean block of wood, or even a brand new brick. I make hoops out of hanger wire and stick them in the medium corners and cover that with plastic film—for example, a dry cleaning bag. We’ll have a picture of this on the website too, I’m sure.
It’s O.K if the covering is loose. I kind of like it because if it moves, there’s a bit of ventilation. And the air movement, for my cuttings, it still keeps the humidity but it tends to not let them rot and make the new growth kind of more stiff and leathery, if that makes any sense.
Margaret: Yeah. Yeah. So basically what we’re doing is we’re preparing our own little germination chamber because we don’t have a greenhouse, right? So this is like our mini impromptu greenhouse and it’s a flat and it has drainage holes. And it has a clean medium, so a sterile medium that’s fresh, not recycled potting soil, so we’re not bringing in pathogens. We want to keep it humid, but we don’t want to suffocate them and rot them either. Right. And so you just put hoops over, as you said, and people could improvise and use whatever to figure, to have enough headroom for the cutting.
Ken: As long as it’s something really clean.
Margaret: Yeah. O.K.
Ken: This is something that you might do or might not do. But some people you’ll see pictures of a glass jar put over a cutting, that doesn’t work for me. Or a closed plastic propagator with a rigid plastic top. I think that these cuttings need ventilation.
Oh, and don’t put it in sun, full sun. It should be in very bright light. And if there’s, as I said, if there’s a little breeze, that’s just swell. And label the kinds of plants. You can keep opening it up and adding more cuttings and adding more cuttings, and just put them in rows and label them and keep each type together so that they root about the same time.
Margaret: Ah, O.K.
Ken: No, that’s the big deal. Now, if I’m just taking a few cuttings, I don’t have to exactly do that, I can use a super-clean 4- to 6-inch plastic flower pot [below], either a brand new pot or one I’ve washed or put in the dishwasher. And square pots are good, because if you line up square pots in a flat, they won’t fall over [laughter]. And they also have more room. Round pots, you pick up the flat and they all go everywhere. And you can use a larger pot. You could even use an 8-inch pot if you wanted to have six cuttings of the same kind of plant or something. But I think 4 to 6 would be good.
Ken: That’s a smaller-scale version of the sweatbox. And then I gather plastic bags like the ones that come on a roll at the supermarket for vegetables and fruits. And I also might get some zipper-lock plastic bags. When I’m ready to recycle the supermarket bags, I turn them inside out, because I don’t want the fruit juice or vegetable juice to be on the inside.
Margaret: Right. I, a lot of times, wash them. And then I turn them inside out and dry them like on some… Like in the dish drainer where the silverware is, I’ll put a spatula and a wooden spoon—something tall—and I’ll drape them over that inside out, upside down, you know what I mean? And they’ll dry. Like hanging out the laundry.
Ken: Margaret, that’s great.
Margaret: Yeah. Well, you know me, I’m up-cycle, recycle over here [laughter].
Ken: Problem solved.
Ken: So the flower pots are going to be filled with the medium, and those are going to be put into the bags. And if it’s those vegetable plastic bags, you can pull up the sides and they’ll often stay up by themselves, but sometimes they flop and you don’t want them to lean on the cuttings.
Ken: I find that if I put a rubber band around the pot, that helps keep them up. And sometimes I’ll use a bamboo skewer, like the kind you use for barbecue and stuff in the corners of a square pot.
Margaret: Oh, that makes sense. So we could do an individual little mini-propagation thing if we’re just going to go out and take a couple of cuttings of our elderberry, because we were going to make more elderberry for the birds or for elderberry, whatever, cooking, jam, etc.
Ken: Or if it’s variegated or gold.
Margaret: Oh, so that’s another reason that you might-
Margaret: O.K. Let’s just talk briefly about that. Because I kind of get the logistics, the basic logistics, but so… Oh, and I meant to say, do you use rooting hormone? Because I mean I think that probably-
Ken: I’ll tell you that in a second.
Ken: That’s an option. But I just wanted to mention that the stiff gallon storage bags with the zipper closures, especially if they’re high quality, usually stand up by themselves. And if the cuttings are really small and short, the whole thing can be slipped in sideways in the bag. That was just something to mention.
Getting to the hormone, let’s talk about where we’re making the cut. Because we’ve talked about how long that cutting’s going to be, and we’ve snipped it with our Felcos or something out in the garden and put it in the water. And now we have to recut it.
So most softwood cuttings are nodal. And that means that they’re cut just below the leaf joint or node, the place where leaves emerge. And you remove the bottom leaves by pulling them off or by cutting them with a super-clean knife or a new single-edge razor blade. And you trim those cuttings just below that node. And if you’re using rooting hormone, powder or liquid, you dip that fresh-cut stem in the hormone and follow the directions on the container. I mean, we can’t really give blanket advice because there’s all different kinds. Just read it.
Margaret: And it’s important that you don’t stick every cutting into the little jar of the product. You put a tiny bit in a saucer or whatever, in a vessel that’s not for eating and so forth. Do you know what I mean? You’re not sticking things into the… Yeah. Again, follow the directions. Yeah.
Ken: Right. You usually dilute if it’s liquid.
Margaret: Right. Follow the directions.
Ken: If it’s powder, sometimes, it depends on the container, I might use the cap. But something small. And you just want to dip it and you could tap it to get the excess off. But you don’t want to take it all off. But when you make that cut, it’s moist. So it really does cling to the cut.
So now I go back to my rooting medium, and I’ll make a hole in the medium deep enough to take that cutting, so that the lowest node is just below the surface. And I use a clean pencil to make a hole. I label the pot, or I promise I’ll label the pot, and then I forget.
Margaret: Yeah, good luck with that [laughter].
Ken: Label the pot. And press the medium—for example, my perlite—back around the cutting. And I do it so it makes perfect contact; I do it kind of hard. You can also use water, poured gently from a small watering can to settle the medium around the cutting. And you mentioned how commercial growers use mist and humidity is high and the cuttings are kept cool, and they usually have bottom heat. But that’s not really practical for us [laughter]. But in the summer, when it’s humid and warm outside, we sort of have that condition.
Margaret: Right. And again, not in direct sun because we’re not trying to parboil these things, right? Bright light but not direct sun, right?
Ken: So you place your cuttings or your pots in bags, in a spot outdoors where they get very bright light, no direct sunlight, like you said, and it’s fine if there’s a gentle breeze, and you check the medium to keep it moist.
In the time that it takes to root, which is often three weeks or so, it doesn’t even dry out. It doesn’t have time to dry out. It kind of depends on the cutting.
If you see new growth on the cutting, it’s probably got roots, too. Sometimes they recommend giving the cutting a tug, but I’ve torn roots off doing that [laughter]. So I usually take a butter knife and pry it up in the perlite to see if there’s roots. And if there are roots are about 1 inch long, it’s great, that’s it. If there are no roots, you can just stick it back into the medium.
And then when it is rooted, you can pop up the rooted cuttings individually. And just like with seedlings, you want to harden it off for a week or so. So you put it out of sunlight, in a protected shaded spot.
Taking softwood cuttings is so satisfying, because the success rate is so high, and you can make more plants to use in the garden if you wanted to make a hedge of something, or more likely to give as gifts, or maybe there’s going to be a plant sale, something like that. When you give a visitor a plant to take home, well, that’s how we got so many of our plants. And then you look at that plant and you remember the person. This is a win-win.
Margaret: So you mentioned that, for instance, if you were to see a variegated piece of something, of one of these easy-to-do shrubs, you might try to propagate that to see if it could then become a permanently variegated specimen. Is that what you’re saying?
Ken: Yes. With growth above the ground, it almost always remains variegated. I have a gold-leaf Sambucus that’s an American Sambucus. I have a variegated Sambucus with white edge, and they’re like two and a half weeks you’ve got roots.
Margaret: And that’s elderberries, yeah?
Ken: Elderberries. Right. Ornamental.
Margaret: Yeah. Yeah. Yeah.
Ken: I guess I’m saying ornamental elderberries because they do fruit but… It’s a little dangerous to say this, but if the fruits are black, generally they can be used for jam or something. In Europe, they cut the flowerheads and dip them in batter.
Margaret: Yes, I know.
Ken: And fry them. I don’t do that. But I think that if the berries are red, you leave them for the birds.
Ken: And that might be the American one. Anyway, we’re not dealing with that.
Margaret: Yeah. And so then the aftercare is like any new young thing and like you said, you harden it off and you tend to watering and so on and so forth. And it’s going to take a number of years, depending on what it is, to grow into something that you’re going to put out in the garden. It’s not instant. But it’s free [laughter].
Ken: You can put it out in the garden that year in some place.
Margaret: O.K. If you can take care of it.
Ken: Well, or maybe you make a splinter nursery or something, which I do. If something takes three years to become a 4-foot shrub or a 3-foot shrub, it always seems like, “Oh my gosh, that’s so long.” But think of all the things we’ve planted that we thought we’d never see, or that it would take too long. And you’re not standing there tapping your foot and watching it. And before you know it, it’s a shrub.
Margaret: Right. Right.
Ken: I guess if you’re going to plant it directly in sun from that hardening-off place, you might want to put some… I was going to say Reemay or something, but I used to use old kitchen curtains that I found. The polyester, gauzy, translucent curtains.
Margaret: Yeah. Shade cloth [laughter].
Ken: Shade cloth, right. I put it on a couple of stakes, make a little tent for a couple of days. And then the little baby shrub can be in full sun. You’re talking about this and I’m looking out the window at 5-foot-tall shrubs that started as cuttings.
Margaret: Right. And the thing is, if you do it judiciously, if everyone were to go try this—and we’re encouraging people to try this, this is fun, and it’s exhilarating, if it works, to make more plants of any kind. And it boosts your confidence, plus you can share, which is great or repeat, as you said, whether for a hedge or otherwise. You know what, some of them may not work. I know people who say, “Oh, roses are easy to do like this.”
Ken: Oh my gosh.
Margaret: I guarantee if I tried it, they would rot off and get fungal diseases and whatever. So you just never know, from one person to another, who’s going to have success. The timing can be different. The variety or species is different. Do you know what I mean? There’s so many variables. The humidity, the temperature, the blah, blah, blah, blah. So we’re just saying, try it, and you have nothing to lose except some snips from this shrub or that shrub that you can take judiciously. It’s not going to mar the shrub, right?
Ken: Yeah. I think there’s some people who are born to root [laughter].
Margaret: Yes. Yes. Yes. Our friend, Adam Wheeler at Broken Arrow nursery is a master propagator. He could reproduce anything. He’s amazing.
Ken: We used to say, “They could grow an oak tree from a pencil.”
Margaret: Yeah. Any other key points that we didn’t cover? Because I was going to bring up some stray thought over here, as usual.
Ken: I talked a lot about the sweatbox [above]. But you could start small. Start with one pot with some medium in it. And one plant in a plastic bag that’s open. Or a couple of woody deciduous, flowering shrubs. And if at first you don’t succeed, you’re going to be a gardener.
Margaret: Yeah. Yeah. Yeah. Indeed.
Ken: Have you ever killed a plant without learning something?
Margaret: No. No, that’s absolutely true. That’s absolutely true. So yeah, so lots of propagation at this time. I mean, it’s time for successions of many things in the vegetable garden and even in the flower garden. Like my flower farmer friends are sowing more zinnias and marigolds and cosmos so that they have them well into fall.
Ken: Oh, second sowing. Yeah.
Margaret: Oh, they do four or five, the flower farmers. Yeah, they do four or five sowings. Yeah, it’s crazy. But beans, greens, lettuce, arugula, cilantro, basically everything in the vegetable garden except tomatoes, peppers, eggplants, potatoes. Those long season or tuberous things. You start over, you keep going, otherwise you don’t have any veggies in September.
So, yeah, there’s a lot of propagation at this time. We’re just encouraging people to try this and get excited about it and feel good when some of them work. And then you’ll always, like you just did, look out the window at that shrub and go, “I grew that.” Right?
Well, thank you, Ken, for the lesson. And people shouldn’t forget that next Thursday we’ll have the information on next Thursday night, the 17th of June, 2021. They can join this fundraiser for Rutgers Gardens that’s honoring you. So thank you.
Ken: Oh, thank you. That was great.
Margaret: Go take some cuttings.
Ken: It’s the time. It’s the right time.
(All photos by Ken Druse.)
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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 11th year in March 2020. 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 June 14, 2021 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).