dennis schrader’s tips for overwintering tender plants

I THINK OF THEM as investment plants, plants that might not be hardy where I garden, but that with a little extra work and the right strategy can be carried over year to year, even without a greenhouse or the perfect spot to do so.

Nobody I know has more investment plants than the list of 1,600 unusual annuals and tropicals that Dennis Schrader and the team at Landcraft Environments propagates to sell wholesale to nurseries, landscapers, and botanical gardens. (Follow them @landcraft_environments_ltd on Instagram.) With his husband, Bill Smith, Dennis Schrader has since 1992 operated Landcraft Environments in Mattituck, Long Island—specialists plants that add seasonal color and texture, and the look of the tropics to the garden. (Like the coleus called ‘Fishnet Stocking’ above.)

He’d like to encourage us to start a collection, too, and offered tips on how to keep them happy—tactical advice on plants we should consider investing in. Our conversation started with a “New York Times” article I wrote a couple of weeks ago on the topic, and continues here.

And we also talked about the emotional side of carrying a plant over year to year and beyond. It turns out I have a plant I got from Dennis decades ago that I have been stashing every winter since—and that he lost one year to disease. Guess what’s heading back to him from my garden soon? (Below right, Dennis with Bill Smith, in a photo from The Garden Conservancy.)

Read along as you listen to the October 2020 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).

the mad stash: overwintering with dennis schrader



Margaret Roach: How’s it out there?

Dennis Schrader: Fall is here.

Margaret: Yes.

Dennis: It’s great, it’s cooling off, very nice.

Margaret: Yes. So before we get started, I should say I was so happy that we did that “New York Times” story together a couple of weeks ago about this subject, the mad stash, right?

Dennis: Yeah, yeah. It was fun.

Margaret: And thank you … it was very popular, and it was fun to read the comments. Lots of people jumping in and saying their successes and their failures with different plants, you know?

Dennis: Mm-hmm.

Margaret: So this is something people love to do, is to try to figure out, right, how to carry over a beloved plant, so-

Dennis: Yeah.

Margaret: You identified several sort of tactical categories, like … because not every plant will want the same thing, to survive the winter in this sort of false environment, not their native habitat. And I just wondered, can you tell us about sort of how you group them, and how you thought about that?

Dennis: Yeah. Well, first off it’s … We get these plants, these are given to us or purchased, and we nurture them all summer, and then we want to do something with them, just not have them hit by a frost and that’s it. So a lot of it has been experimenting with different types of overwintering. So some of the easiest ways are collecting from seed, and doing cuttings, or even actually just bringing the plant inside and treating it as a houseplant. There’s different ways to store them.

Margaret: Some are even stored dormant, like bringing it in as a houseplant and keep it awake, or bring it in-

Dennis: Right.

Margaret: …as a houseplant and let it nap. And that’s one of the things that I frequently, earlier on in my gardening career, I used to try to keep everybody awake, and some would rather go to sleep, right?

Dennis: [Laughter.] Right. And you also run out of room; it’s a space issue most of the time.

Margaret: Yeah.

Dennis: Yeah, so I’ve tried even hibiscus bushes and Brugmansia that would normally grow all year, those just putting them in the basement and keeping them on the dry side and dark. And they’ll have some dieback but then you get them going in the spring and they really take off. Because most plants do have a slowdown or dormant period, either from cool or in the tropics a lot of times it’s from dry weather. You’ll have a rainy season and then a dry season. So there is … you try and mimic maybe the dry season, and just let them defoliate and rake up the leaves, and hold on to them until spring. [Above, variegated Brugmansia ‘Sublime’ from Landcraft.]

Margaret: Even I think that you recommended that for some of our fancy-leaf geraniums, yes?

Dennis: Yeah. Oh, sure. Yep. I know someone that used to hang them, who would bare-root them and just hang them in their basement, and then plant them again in the spring. So it can be pretty radical.

And what I find also is if you have success with one type of plant or a treatment of one type of plant, try it with some other ones. I had another friend that used to keep Ensete, the red-leaf Abyssinian bananas, he would … It got so big, with this huge trunk, he would keep it under his dining-room table [laughter]. So it would do fine, except you were kicking it, you would think it was a dog or something under there, and you look and it’s this 6-foot stump. But it worked for him.

Margaret: So the banana under the dining table, is that going to be in the reference book about this? [Laughter.]

Dennis: Yeah, right.

Margaret: So what we’re really trying to do is we’re trying to sort of categorize things as we look around the fading garden right now, wherever we garden, and match them to the right tactics. So like with seed, like what would be the kind of … What are just a few examples of things to do from seed?

Dennis: Oh, zinnias, marigolds, those are some of the common annuals. Abelmoschus. And the plant kind of lets you know when it’s done blooming, it’s starting to turn a little bit brown, looking a little bit dry. And it’s shorter days, cooler weather, those are all indicators to start looking. Morning glories are another, the vining morning glories.

And they start looking a little tattered [laughter], like they’ve done their big show for the season, and then it’s time to harvest. And you want the seed pods to be ripe, but not ripe enough where they open up and a lot of plants will expel their seeds and kind of open up and shoot the seeds around. You want to wait before that happens, or else use some kind of a net bag or something like that to hold the seeds, catch the seeds.

So commercially, we go out twice a week and do the rounds to all the seed plants that we’ll be collecting. And usually we’re right on top of it.

Margaret: I loved the pictures that you sent me for the “New York Times” article that you took for us, that were like these turkey trays, the aluminum-

Dennis: Right.

Margaret: [Laughter.] Roasting pans. Filled with seeds, like someone in the staff would cut off the flower stems that were dried into these pans and it’d be like trays of them. I guess you bring them in to dry? [Above, Dennis’s photo of black-leaved cotton seedheads in the aluminum trays at Landcraft.]

Dennis: Yeah. We keep them on racks, basically, not oven racks but just like on a cart, and we keep them in the trays. Some of them we have to cover with … When we get corn, ears of corn, it’s that net bag, or you get bulbs in them–sometimes we keep them covered with that because they do shoot and explode, kind of. So each one has a little kind of nuance that has to be taken care of. But basically it has to be dried, and good air circulation—that’s why we keep them on the racks. And then when they’re totally dry, we bag them in Ziploc bags, most importantly: labeling them. And then we store them in a dry, cool place.

Margaret: Did you like … When you first started doing this, and you started to ramp up and realized this was … I mean, you were doing a landscape design-build kind of firm years ago, and then you couldn’t get the plants necessarily that you craved for your clients and your designs, and you started little by little—I’m oversimplifying—but you started little by little to propagate them yourself. And then oops, suddenly you ended up with a farm and a greenhouse range, range of greenhouses and a business doing this-

Dennis: Right.

Margaret: Wholesale, but did you like … I mean, a lot of the things that you have become known for and have disseminated into the garden trade, they weren’t like the mainstays like marigolds and petunias or whatever. You have those, but they were unusual things. So did you look up the life history of the plant and like what its native surroundings are, like how did you figure it out, or researched in books, or how did you know what to do?

Dennis: Well back in the day there wasn’t Google to check things, or the internet, so-

Margaret: Without Google.

Dennis: Yeah, a lot of it was reference books and then also just trial and error. Some of the seed catalogs, like Thompson and Morgan, they list thousands of thousands of plants, and one of the inspirations was seeing all these plants but like where can I get these? I’m going to start growing them.

And yeah, it was just hunting, finding things, and one of our plants I found… it’s a roadside weed in Costa Rica, but it’s got this great silver foliage and little pink flowers. So we find things all over the place, and trading with friends and institutions. Like our black-leaf cotton, which we got originally from Wave Hill, and it was way back when Marco Stufano was working there. And he gave us some seed, and we kept it and were growing it for years, and then one year they lost their crop, and it got too cold before it set seed. So then we gave it back to them, and the same thing happened to us, we lost the seed and they gave it back to us. So always a lot of sharing.

Margaret: Penpals.

Dennis: Yeah, right, seed pals.

Margaret: Well and it’s funny, when we did the “New York Times” story again recently, we were talking about storing bulbs and bulb-like things, tubers, and so forth, and we can talk about those in a second. But I said, “Oh, yeah, when I store my Canna musafolia, or Canna ‘Grande’” [above], and you like interrupted me, you’re like, “You have that? I think that came from us.”

Dennis: [Laughter.] Yep.

Margaret: And you don’t have it anymore.

Dennis: Right, yeah, we … with the mosaic virus we had to get rid of our stock and so I’ve been looking for it, so-

Margaret: Well guess what?

Dennis: I’m still waiting for that package to come. [Laughter.]

Margaret: There might be a package heading south. Yes, there might be a package.

Dennis: Great.

Margaret: I’ve been collecting sturdy boxes since we spoke. And that’s what I love about horticulture, really, is like the remembrance of where every plant came from, like you just said that roadside weed with the silver leaves in Costa Rica—the provenance. And do you know, that sort of sense of … Dan Hinkley and I were talking about this recently because of his book about his garden at Windcliff-

Dennis: Right.

Margaret: …on a recent program.  And how he walks around every morning in the garden and he sees his friends’ faces, because of the plants. You know what I mean?

Dennis: Yeah, that’s so true.

Margaret: You must have that, too.

Dennis: Yep. We have a lot of plants from the original Heronswood Nursery. And some of them even have those little blue labels sticking out of the ground.

Margaret: That’s so funny, because that’s what I started when we did our interview recently, I said to him, I did the intro and said, “Every year when I do my spring cleanup I find turquoise plastic labels in my garden.”

Dennis: [Laughter.] Right.

Margaret: Yeah, so we’re all just one big, happy, crazy family.

Dennis: Yep.

Margaret: So you said before “trial and error,” that that’s how you learned it in some cases. And one thing that for me … You have to be willing to invest, and maybe the investment doesn’t pay off, right, like any investment. So I bought phormiums years ago, I love the New Zealand flax, the sort of vertical almost effect … It looks grass-like but it’s broader-textured foliage, colorful-

Dennis:  Similar to iris foliage. [Above, at Margaret’s, gold Phormium in a big bowl with Coleus and Alternanthera.]

Margaret:  Yeah, they look like iris-

Dennis: But colorful, very colorful.

Margaret: Yeah, and I love them in the center of big pots and stuff. And they’re not cheap at retail, and I wanted to carry them over. And I failed a few times, and I think that’s … But it was worth it because now I kind of nailed it and I was trying to keep them too warm. I was thinking they’re from a warmer zone, so I … You know what I mean, I was trying to keep them actively growing almost, and that’s not good.

Dennis: Yeah.

Margaret: It didn’t work.

Dennis: No, they would want to cool down, and just stay right above freezing. Or just in the high 30s is fine for them. And on the dry side.

Margaret: And you would never think that at first. We think tropical or subtropical, or tender, and we think “Oh, got to keep it warm, got to keep it warm.” But it’s a little counter-intuitive, right?

Dennis: Yeah. Well a lot of South African plants like Agapanthus are similar to that, where they can just be right around freezing and they’ll be all right. Chondropetalum, a grassy plant, and a lot of the Restio. You know what else is interesting, is if a plant is grown at a higher altitude then a lot of times it can take cooler weather than you would think, even if it is a “tropical” plant.

Margaret: Right.

Dennis: It’s much cooler up at higher altitudes.

Margaret: Right. And compared to trying to push them in the low-light season here in the north, push them to keep growing, to stay active, it’s more merciful, really.

Dennis: Yeah. Let them rest.

Margaret: To let them slow down. Right?

Dennis: Winter rest, yeah.

Margaret: Right. Even if like the phormium they have foliage, and so they don’t want to be in the dark in the cellar with that Pelargonium, the fancy-leaf geranium we were talking about. Or the tropical hibiscus, that’s going to be leafless, or the Brugmansia that are going to defoliate, right?

Dennis: Mm-hmm.

Margaret: So not like that. But also not warm and actively growing and being watered once or twice a week, etc. It’s like we’re backing off on everything and letting them just hover in a way, some of them.

Dennis: Right. I have like a covered porch that you would want to use for three seasons, and then in the fourth season you can store plants in there sometimes if it isn’t going to freeze, or you just put in like a minimal little heater or something just to keep it above freezing. And sometimes that’s all you need, and it’s a nice, sunny porch, but … Or if it’s attached to a house, sometimes that even makes it warm enough. You just open the door and let it warm up.

Margaret: I had an insulated garage and there was a window that was on the bright side, and for some reason those phormiums just … It was super-cool, but there was plenty of light and they just did so much better than where I tortured them in the past. So you know.

Dennis: [Laughter.] Yep, yep.

Margaret: So people may be looking outside now or soon, depending on where they live, and like, “Oh, the dahlias got frosted. Oh, the cannas got blasted with frost.” And they think that’s it. But it’s not it, is it?

Dennis: No, it’s-

Margaret: Those are some of the easiest, right?

Dennis: Yeah, that’s the signal that it’s time to harvest, especially dahlias. Because they’re such … usually, most of them are just late-season and they enjoy this cool weather. Like right now our dahlias are going gangbusters, in full bloom, and we’re getting big bouquets every day. And then after we have our first killing frost, where it’s down below 32, and then the foliage will turn brown or black, and the plant might even get a little mushy, but you dig it out and cut it off leaving about an inch or 2 of stem, and then you have all the bulblets hanging out like fingers almost. And just keeping them, and then actually packed into crates or bags with either mulch, or hay, or peat moss, or wrapped in newspaper, there’s so many different techniques like that.

Margaret: And do you dry them first; do you sort of cure them first a little bit?

Dennis: Yeah, yeah, we let them air-dry for a couple of days. And then again … It’s almost like I tell people to think about it like overwintering potatoes. If you have like a root cellar, you’re trying to mimic the root-cellar condition, a dark and cool but not freezing. [More on stashing bulbs and tubers.]

Margaret: So 40s maybe.

Dennis: Potatoes will last for a long time, and if it’s too warm you’ll see they’ll start growing. So it’s the same thing with dahlia bulbs. Or cannas, Eucomis.

Margaret: Yeah, the Eucomis [above] are funny, they’re the pineapple lilies. I had bought them over the last … They’ve become sort of a thing, a popular thing, increasingly so, and you have a lot of nice selections with pretty leaves, purple leaves or spotted leaves or whatever, besides the flowers. And I’d always just drag the pots in. I’d have them in pots and I’d drag the pots in because I’m in Zone 5 so they aren’t hardy in the ground. But the pots, it’s heavy getting them into the basement, all that, and I guess could I unpot more of these things? I mean, I guess I could unpot them.

Dennis: Yeah, those could be … Because they are hardy into Zone 7 and occasionally in 6 with some mulch, but they could be bare-rooted and again put into a net bag or a crate or something and stored that way.

Margaret: So in like bark mulch or something like that?

Dennis: Yeah, bark mulch, straw, hay, hulls, sometimes there’s rice hulls or even packing peanuts. If you have a box with packing peanuts, you get a shipment in with something, that works.

Margaret: Now I’m saving those to ship you the cannas. [Laughter.]

Dennis: I’m going to keep my eye out for that.

Margaret: Yeah. So do you … O.K., so say I have the dahlias and I’ve let them get frosted. And I’ve cut them back and I’ve dried them for a few days or a week; I’ve let them cure a little bit. And then I’m going to pack them. Is it important to keep each clump of tubers or tuber separate, like not just throw them in a big pile together in the packing material? Should there be packing material between each one or do you wrap them in newspaper first, or any other sort of tricks, and then like check on them?

Dennis: It’s really what you have time for and how you’ve had success. We’ve done it both ways: individual wrapping, again, something really important with dahlias is labeling if you need specific colors. But I always recommend trying something, and if it works then just keep doing it. If you’re doing something right, like your Phormium, you finally found something that worked for it, and then try some other plants maybe that would fit into that category and make it easier for yourself. You don’t want to make it too much of a chore.

Margaret: Right.

Dennis: Sometimes we’ll divide them all, spray them with antidesiccant. Well actually we let them dry and then spray with an antidesiccant, and then wrap them. But that’s … we’re trying to keep as many as possible for as long as possible, too.

I think cuttings, that’s another way to go out and just start taking cuttings, you don’t want to wait too late in the season for that, but that’s another great way of overwintering plants for some of your favorite plants.

Margaret: Like coleus.

Dennis:  [Laughter.] Yes. Yeah, coleus is very easy, root right in water.

Margaret: Yes. And those sweet potato vines.

Dennis: Yeah, yeah. Like salvias, some salvias, begonias, impatiens. There’s a lot of things that you can root in water.

Margaret: Yeah I wanted to spend the last couple few minutes I wanted to know are there some … You have 1,600 kinds of plants in the list right now. And by the way, people can’t order from you as individuals, but you do ship [to retailers] in the mid-Atlantic and Northeast and so forth, and from like Maine to Maryland. And you have a list; I’ll give the link to the list of retailers on your website.

And I’m just going to say out loud to people: I go to my garden center in the offseason and I say, “What are you ordering from …?” I ask them about things that I want that are on a wholesale list like yours and nudge, nudge to order a tray of something.

Dennis: Oh, sure.

Margaret: You know what I mean, it’s O.K. to ask our garden centers to think about specific items, right, that they can get from wholesalers that we can’t? So-

Dennis: Right.

Margaret: …be bossy.

Dennis: We do that a lot, we’ll get a special order from a garden center specifically for a client. So that works well.

Margaret: So don’t be afraid to do that, everyone listening. Because it is possible, and the garden center is still going to make the markup, it’s not like you’re inconveniencing anybody. So anyway… But are there some, in the last minutes, are there some hot tropicals or unusual annuals that you’re wanting, craving, besides the canna that I’m sending back to you [laughter], that you’re wanting to find that add to the palate, is there like a thing right now that you’re after? On the hunt for?

Dennis: Oh…

Margaret: You have everything.

Dennis: Yeah. Yeah, there’s a lot. I really like colorful foliage. Or variegated foliage; I just love variegated foliage. And just oddball things. I’ve been collecting for myself now just a lot of caudiciform plants, with like big, fat bases on them.

Margaret: Yes.

Dennis: We do offer a few. I know this-

Margaret: I didn’t know that, that you did that, because I have … My oldest houseplant is a … well, it’s now called Pseudobombax, but it was called Bombax ellipticum, the shaving brush tree.

Dennis: Oh, yeah. Mm-hmm.

Margaret: And it’s massive in my living room, I’ve had it for about 30 years. And I grow a number of other things with swollen bases that are like their storage organs. Huh. [Above, the caudex or storage organ of the Pseudobombax houseplant in a big pot at Margaret’s.]

Dennis: eah, I just started collecting them years and years ago, and we have a nice collection, and we also do have some that we can sell. And we do sell. Yeah.

That, foliage color, there’s always new cultivars coming out, the great elephant ears with different shaped leaves. There’s one, it’s called ‘Pharaoh’s Mask’ [below] that almost looks like a wrinkled forehead, and it’s apple green with these dark stripings on it. It’s kind of interesting.

Margaret: Wow.

Dennis: Yeah.

Margaret: Not so many years ago the elephant ears, it was like just the plain old elephant ears and now, wow.

Dennis: Yeah, there’s hundreds of varieties.

Margaret: Yeah. And I’m always experimenting with which ones want to be kept sort of half-awake like a houseplant, and which ones want to go to sleep, and oh boy, that’s a whole other subject.

Dennis: Yeah. Yeah, as a general rule of thumb Alocasia usually do better as houseplant than Colocasia.

Margaret: O.K., all right.

Dennis: Yep.

Margaret: Well, Dennis, I had such fun and like I said I can’t wait to pack up the goods and send them down there because it sort of completes the circle for us.

Dennis: [Laughter.] And we’ll have it for you next time if you need it.

Margaret: Yeah. No, it’s sweet, it’s really sweet. But I’m so glad to reconnect and learn more, and thank you so much; thanks for making time for us today.

Dennis: Oh, very welcome, great speaking with you. [Below, garden doodle by Andre Jordan.]

more overwintering ideas

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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 October 2020 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).

  1. Alice Peach says:

    As I’ve said before, my Ficus benjamina (named “Montgomery”) made us move to Arizona from Virginia so he wouldn’t get overwintered in the garage anymore and so he could get out of his pot. I purchased him 37 years ago; I’ve had Montgomery longer than I’ve been married and he has served as a Christmas tree on several occasions. My husband still can’t understand why I dote on him.

  2. jan says:

    Another great podcast. One thing I learned about labeling bulbs/tubers…use sharpie to write the name on the bulb/tuber. I purchased some dahlia bulbs from the CT Dahlia society, and they had the names in sharpie on the tubers. It was great. So I’ve started labeling mine. That way when I give some away, or go to plant them, the are “pre labeled”. Also works great with pineapple lilies, voodoo lilies, etc.
    I also appreciate the “memory” that plants provide…of who I got it from and who I’ve shared it with. One of my favorites is “Aunt Flor’s Begonia” – I haven’t been able to find out what variety it is, but I got a cutting over 20 years ago from the begonia at my Aunt Flor’s house. My Aunt Flor passed away many years ago, but I have a “mother” plant and share many cuttings…and when people ask what kind it is, I say its “Aunt Flor’s Begonia”.
    a great book that I refer to for overwintering plants is “bulbs in the basement, geraniums on the windowsill” by Alice and Brian McGowan. I put different colored tabs on the pages of my plants to correspond with the suggested technique to save/overwinter them.

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