ecological resolutions, with uli lorimer of native plant trust

LIKE EVERYONE around this time of year, I get into a “looking back while looking ahead” combined mindset. Today I want to do just that, but with a sort of ecological filter, taking stock of how things in the garden fared in the bigger environmental picture and what opportunities lie ahead for me to read nature’s signals even more closely and be an ever better steward of the place.

Who better to talk about that with than my guest, Uli Lorimer, director of horticulture at Native Plant Trust, the nation’s oldest plant-conservation organization.

Uli Lorimer, author of “The Northeast Native Plant Primer” (affiliate link), has made native plants his life’s work. In 2019, he became director of horticulture at Native Plant Trust, which was founded in 1900 as the New England Wild Flower Society. Previously he was a longtime curator of the Native Flora Garden at Brooklyn Botanic Garden.

Those are Eastern hemlock cones (Tsuga canadensis), above, in a photo by Uli, and we talked about how vulnerable certain plants like hemlocks are in a changing climate; about the critical need to develop regional seed sources for native plants; and about how to read the clues your landscape is giving you on what to plant where, and how to care for it.

Plus: Comment in the box near the bottom of the page for a chance to win a copy of Uli’s book.

Read along as you listen to the Dec. 25, 2023 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 (and browse my archive of podcasts here).

ecological thoughts at the new year, with uli lorimer



Margaret Roach: Happy almost New Year, Uli. Who knows what-

Uli Lorimer: So hard to tell these days.

Margaret: What a crazy-feeling year here for me, and I’m sort of across Massachusetts, over the New York border from you, but it’s the same place I’ve been in for decades. And this might sound familiar to people:

I’ve been here a long time, but it felt sort of unrecognizable [laughter]. Relentless amounts of rain, I had my first spongy moth infestation ever, jumping worms at epic levels, no real winter yet even though we’re really nearing the end of the year, and all capped off by the USDA’s new hardiness zone map that moves me, once again, half a zone warmer. So I’d love to start with your feedback, as a native plant-focused person, on the new map, for instance, because that’s kind of timely.

Uli: Yeah, I mean, I can’t say I was surprised to see the zones inch up a little bit more, and I think it’s just another way of marking that climate change is real and it’s here. And if you look at the longer period of time, let’s say the last few decades, you can see how dramatically those ranges have shifted. I feel like the news is mostly met with a positive note, and folks thinking, “Boy, I can grow more tender perennials now,” and different things that maybe weren’t fully hardy in our zone now.

But I had a slightly different reaction, and I thought about plants that really like cold conditions, and things that need deep cold winters. And I’m thinking of all of the lovely plants that you could find just across the Hudson River up in the Catskills, for example. So balsam fir forests that only exist currently above 3,500 feet—those plants are struggling. You mentioned it being one of the wettest years on record, and that came on the heels of a pretty droughty year the year before. And for those forests and those plant communities and all those sort of lovely little treasures that reside within, they’re getting squeezed off the top of the mountain, and that’s concerning.

Margaret: And it’s not just things at high elevation, either. Aren’t there other plants as well that have cold requirements to be successful and thrive?

Uli: Yeah. I mean, back when I was at Brooklyn Botanic Garden, we were doing the New York Metropolitan Flora Project, which is sort of a 30-year look at changes in floristics in a major metropolitan area. And there were records of Cornus canadensis, bunchberry [above, recently renamed Chamaepericlymenum canadense], which is another one of these really beautiful herbaceous groundcovers, last being seen in northern New Jersey in the 1920s, and then now completely extirpated and gone. If we fast forward maybe another 50 years, it may also be extirpated from the Catskills if this trend continues.

And it also makes it harder for native-plant enthusiasts to grow those plants in a garden setting. Here at Garden in the Woods we do grow it, but I don’t think we grow it as well as it does in habitat in those mountainous regions. That tends to struggle, particularly I feel like the issue is not so much cold, but also warm, humid summer nights that these plants don’t like. So it has effect across all of that suite of plants that you usually associate with more northern and colder climates.

Margaret: And it’s not just here, there are examples just like those two in every region of the country that will or won’t acclimate as well or thrive in the evolving conditions, even though they were “native,” that it’s their traditional range, that they’re not going to be as happy as things shift. It’s complicated. It’s very complicated.

Uli: Certainly. The other thing, which is complicated and concerning and depressing and I would love to get all that out at the beginning of the show-

Margaret: Whee! Let’s be depressed. Yay! Happy New Year! [Laughter.]

Uli: …has to do with pest pressures. You mentioned spongy moth. And so with milder winters and not cold winters, it allows for more of those pest organisms to, overwinter, to survive. In some cases, things like Southern pine beetle might even be able to turn over two generations in a single season. And I was just talking to a good friend, Rodney Eason, who worked in Acadia for many, many years, and mentioned that hemlock woolly adelgid is just beginning to show up there.

Margaret: In Maine.

Uli: In Maine. So the iconic Acadia National Park, it’s just beginning to show up, and largely due to the fact that the winters are getting milder and milder and those organisms are not getting killed off by the minus-10, minus-20 degree periods that used to be the normal.

Margaret: Yes. I keep thinking about snow cover, and how growing up in the Northeastern region that we had persistent snow cover for weeks and weeks and weeks and weeks, if not months. And then that’s gradually changed. And I keep thinking about—this is a complete derailment, sorry, but you know how I am, how my brain works [laughter]—but I keep thinking about the subnivean layer, that sort of little layer between the soil, the ground surface, and the bottom of the snow and all the creatures that, in the winter, utilize that area. And I keep thinking: but it doesn’t exist. Where are they all? What are they doing? Do you know what I mean?

Uli: Yeah, yeah. I love that term, by the way, subnivean. It’s just such a wonderful word. No, but not just where do those organisms exist without snow cover, but you lose the insulating effect of the snow and you get more of that sort of frost-thaw cycle with the soil and more heaving, and it really disrupts that entire winter ecosystem when we don’t have consistent snow period and snow cover.

Margaret: Because it had an insulating… It was an insulator, as you’re saying.

Uli: If folks are interested, there’s a really wonderful researcher named Elizabeth Burakowski, I think out of University of New Hampshire, who studies exactly these winter effects on climate change, and what’s happening with the decreased snow cover. And she’s got some really wonderful research.

Margaret: Oh, great. Good tip. Thank you.

Uli: She’s really wonderful.

Margaret: Well, another topic that was probably on the minds of gardeners throughout the country as they closed out the 2023 garden—and some are still doing that right now—and that will be on our minds again as we all look ahead to starting for 2024, is sort of the ethic of gentler care of the garden, especially at those both ends. The so-called cleanups that used to be so fastidious, like such control and domination over all the plants.

And the call in recent years, with ecology in mind, has been to “leave the leaves” and so on. So there’s more and more awareness of that gentler approach, which speaks to a greater environmental awareness, in general, for gardeners. So looking back and looking ahead, what, at Native Plant Trust, at your properties, have you shifted or did you always “leave the leaves”? Both at the fall and at the spring end, the going-to-sleep and waking-up ends of the garden, what’s the guidance and what do you see that has changed recently, or ahas you’ve had?

Uli: Well, for us, I think because the Garden in the Woods is in the woods, so we have to manage a lot of leaves. And so I think that we tend to let them lay where they fall for the most part, although we do, in the Curtis Woodland, we’ve got fairly extensive plantings of Phlox divaricata [above] and Phlox stolonifera, so creeping and woodland phlox. And we found that leaving the leaf cover over the winter actually, it’s not a detriment to the plants, but they do need to be uncovered a little bit in the springtime. And so that ends up, again, it’s sort of like protection and insulation for them. And believe it or not, there’s enough light that filters through so they still are able to photosynthesize. But then those are areas that we try to lightly rake free a little bit ahead of spring growth.

Otherwise, paying attention to where leaves naturally accumulate, both areas where may be little swales, and trying to plan for plants that don’t mind deep leaf litter. So if it’s an area that will accumulate maybe 8 or 12 inches of leaves over the winter, we’re going to put things like Solomon’s seal or ferns, or something that have strong enough growth that they can push through all of that leaf litter and they don’t seem to mind.

On the flip side of that, what we’ve been doing quite a bit, which I really like, is finding spots where prevailing wind patterns keep the ground bare and where moss naturally grows. We’ll try to help that along and kind of keep those moss patches going, and they end up being the really perfect place to display, what botanists like to call “belly plants,” things that you need to get down on your belly to see. So-

Margaret: Belly plants, I love that. [Laughter.]

Uli: So things like Houstonia [bluets, above], things like partridge berry [Mitchella] or trailing Arbutus [Epigaea repens], these really delicate, wonderful spring charmers that would just be utterly lost and smothered if the leaf litter got to be too heavy.

Margaret: So you’re reading the landscape then for clues on places that can accommodate these little treasures, is that…

Uli: Yeah. Well, you think of it this way: Let’s say you really want to have a planting of bluets in a place. You can set yourself up to sort of forever-maintenance, to keep clearing that space of leaves or shredding it and add extra tasks, or work with what the landscape is telling you and shift your planting designs and plans to eliminate busy work, in other words. You don’t have to keep fussing over this one little spot, because the winds keep it clear, and the bluets just seed themselves into the moss and you don’t really do anything.

Margaret: Right, so this and into midwinter and so forth would be a good time to maybe go out and take some notes and observe and write down where those places are in your landscape that nature—the wind patterns because the topography and so forth, and the prevailing winds—seems to leave cleaner [laughter]. That’s interesting. I never really thought about that, but now mental image I’m having of like, “Oh, right, that’s where all my leaves always accumulate, but I don’t have any over there.” Huh. Yeah.

Uli: Well the other thing, the flip side of that, too, is to say that if you’re clearing your leaves from the lawn, and to go back to what you were saying earlier about the “leave the leaves” campaign, I think there is, for some people it looks unkempt or untidy if you don’t do anything. And I think there’s a middle ground where you can still embrace these ecological intentions and techniques and have a garden that looks like you’re caring for it.

And so where I’m driving with this is that many people are creatures of habit, so they do the same thing every year. And maybe you blow your leaves into the same shrub every year. And I think that you should take a look at that practice and say, am I burying this thing year after year, or does it not care? Is it O.K.? I see, driving around, sometimes I see some of the lawn services in homes that abut woods, they’re just blowing the leaves right into the woods.

And I think that accumulation of leaf litter can be bad for some plants. It certainly is the right kind of habitats for jumping worms to get a foothold into. For us here at the garden, we had an area that used to be really populated with a lot of mountain laurels, and they were in decline when I arrived, and I was trying to figure out why. And so I began to dig around at the base of the shrubs, only to find that they had been buried under 12 to 14 inches of leaf mold. And it made sense when I was like, “Oh, because the way the path goes here, we just blow off the leaves into the beds every year in the same spot, in the same spot,” and the shrubs were really in decline because of that.

And so now we’ve shifted our practices, and we rake those and put them somewhere else, and the laurels seemed to be making a recovery. So it was another little aha moment of, maybe be a little critical about how you do your maintenance and if you’re doing the same thing every year. And pay attention and observe. I think those are the two things that gardeners do really well.

Margaret: Another—I call it a trend, but in recent years that I see more and more and people ask me about and I hear friends doing and experimenting with more—is growing things from seed, especially native plants, because a lot of times the ones you’re seeking aren’t necessarily available at anywhere near you. I can buy in from some of the famous longtime purveyors of native plants, who might be located in the Midwest or somewhere else. I can buy in things that technically are native in my region if I look at their range maps and so forth. But it’s not really the local version, the local ecotype; it’s not the local genetics.

And so more and more people are saying, “Well, I really want to find this one that’s really from here, and that’s adapted to here.” And I know you guys are involved in… So what I’m saying is, I think people want native plants that are even more locally native and they are frustrated, so they’re learning to grow them from seed and multiply their numbers of them. But I think you’re doing that on a larger scale; you’re involved with that on a larger scale.

artist Jada Fitch

Uli: Yeah, I mean, so a few comments to make. First, thank you for bringing up seeds, because I absolutely love them. I think, for me, it completes a full circle. When I got into horticulture, you get really attracted to plants and flowers and then to seedheads, and then learning to collect seed and clean and grow them and see that same plant complete that full life circle is just really fulfilling and whole, in a way.

And I feel that many folks who decide to grow their own from seed experience that same joy and fulfillment of like, “Hey, I took this tiny little thing and I sowed it outside and covered it for the winter, and then this magic happened in the springtime, and I got, out of a packet of seeds, I got hundreds of plants.”

And it’s so much more economical that way. And it connects people, I think, on a much deeper level to their gardens when they can say, “Hey, I grew that from seed, and look at it now. Now it’s spreading and now I know how to collect that seed and share it with my neighbors, or cast it about or grow more.”

I think it’s a really wonderful activity. And so there’s some really great folks, and we spoke about this before, the folks at Wild Seed Project in Portland, Maine have really fantastic resources on how to do winter sowing and kind of slow gardening. And they take a lot of the sort of mystery out of it, but none of the magic. And I think that it’s a great resource. [Above, a winter-sowing illustration by Jada Fitch from Wild Seed Project.]

Margaret: And it’s not a lot of fancy equipment. It’s letting nature provide the chill period that’s required for a lot of these native plants to then eventually germinate. And it’s low-tech. It’s just the timing and protecting them from rodents [laughter], so the rodents don’t eat your seed. But that’s the big thing, but that’s about it.

But you’re trying to help, again, unless we collect locally from our own place that we have one plant and we want to have more plants, sometimes it’s hard to get the seed that’s a local ecotype.

Uli: So we’re involved in what’s called the Northeast Seed Network, and this is a very new effort to address that lack of availability of seed in the Northeast. And we’re seeing this from two different perspectives in that folks that are ecological restoration practitioners can’t find the right kinds of materials to put back into wild places after, let’s say, invasive-species removal or mitigation projects. And then certainly the thirst for native plants from the horticulture side has just really exploded over the past couple of years, and it’s hard to find plants, let alone seeds.

So this effort is really aimed at building that supply chain so that we have more people growing plants for seed production, and that can then feed into nurseries that can grow more plants for folks to buy, and that can also supply the restoration industry at scale for the important work that they’re doing as well.

And so we have a lot of wonderful partners from Wild Seed Project, Smith College, Ecological Health Network, some of the local organic farming associations in Connecticut and New York, Hilltop Hanover Farm closer down to where you are, and representatives of some nurseries as well, Pinelands, Planters’ Choice, Van Berkum Nursery. A lot of people are really recognizing that this type of supply chain and infrastructure is completely lacking in the Northeast, and so we’re taking steps to address that.

And so it’s not just the people collecting seed and growing it, but also we’re building proper facilities to clean the seed and house it so that it can be made available throughout the year.

Margaret: It was originally someone at Cornell who told me about it, actually; I learned about it from someone at Cornell University who does the Native Lawn project there. He turned me onto it. So yeah, it sounds very interesting.

Uli: Yeah, it’s just getting started, and I think that in the coming years we will really going to be building out the supply chain, the market, all the educational and workshops and training materials and everything that goes with it. So we’re really excited about the potential impact that this can have for native plant enthusiasts and restoration practitioners in the Northeast.

Margaret: I just wanted to ask you for some looking ahead [laughter]. I mean, we all, as gardeners, we’re all like, “Ooh, I really want to get this plant. I really want to get…” Are there plants that you think of as the wishlist plants of the next wave? That you’d love to see more people grow, or that you guys are increasing or hoping to increase your stock of, or that you just want to put out there as like, “Hey, this is a really great plant.”

Because I think when a lot of us think “native plant,” we go to the regular garden center, it’s like, well, there’s a purple coneflower. But a purple coneflower is [laughter], if you look at the map where it’s native to, it’s not native to most of our areas at all. So I’m just wondering if—and again, people are in all different regions of the country who are listening—but I was just curious if there’s something that you sort of lust after that you’re hoping to see come to popularity?

Uli: Well, I mean, I think that maybe some people think of this as a boring answer, but I think sedges [Carex] are really, have so much utility and I think we’re just beginning to kind of scratch the surface of the ones that are commercially available. And they’ve got applications from sedges that grow in dry sand, all the way to ones that will grow in standing water and everything in between. And I think of them as sort of the glue or the matrix that ties together your asters and your goldenrod and all the other sorts of more colorful plants. [Above, Pennsylvania sedge.]

Because we’re also a conservation organization, I’m always inherently interested in more unusual plants and rare plants. And so I think that we need to find a good way for gardeners to ethically have access to those kinds of plants. And this is sort of a bigger conversation that has to involve natural heritage bureaus and so forth, but I think there needs to be a way that people can support plant conservation in their backyards as well as supporting insects and wildlife and birds and butterflies with all of the common things as well. So that’s something that I would love to try to advance those conversations next year because there’s some really wonderful plants that ought to be more available for folks to grow.

Margaret: Right. And then there’s just things that grow that we have always grown and we’ve all been digging them out for so long, and maybe we should give them a chance to stay awhile. I’m thinking of pokeweed [laughter]. I have a magnificent specimen of pokeweed in my backyard right now. And for so many years I pulled it all out. I dug it all out madly. And it’s fabulous, right?

Uli: It’s tough to get rid of.

Margaret: Do you know what I mean? I mean, the birds love it [laughter].

Uli: Yeah. No, I mean, the fruit has huge wildlife value. And I think I even remember there being a chartreuse selection at Wave Hill when I first started there and I thought-

Margaret: Oh, interesting.

Uli: This is a plant that most people would immediately rip out, and here they’ve recognized its aesthetic beauty and those hot pink fruit influorescences.

Margaret: Yeah, crazy.

Uli: And I was like, “What a cool plant.” And I was so glad they found a good way to use it.

Margaret: Well, Uli Lorimer, I’m always glad to talk to you. And happy whatever comes next [laughter]. Whether we get a winter or not, we’ll see. And I look forward to talking to you again in the new year.

Uli: Yes, I do as well.

(Photos from Native Plant Trust plant finder.)

enter to win ‘the northeast native plant primer’

I’LL BUY A COPY of “The Northeast Native Plant Primer” by Uli Lorimer for one lucky reader. All you have to do to enter is answer this question in the comments box below:

Is there a native plant that plays a key role in your garden—or that you simply love? (Tell us what region you’re in.)

No answer, or feeling shy? Just say something like “count me in” and I will, but a reply is even better. I’ll pick a random winner after entries close at midnight Tuesday, Jan. 2, 2024. Good luck to all.

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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 14th year in March 2023. 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 Dec. 25, 2023 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify (and browse my archive of podcasts here).

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