ferns as houseplants, with nybg’s mobee weinstein, author of ‘the complete book of ferns’

I DON’T KNOW about you, but I’m drawn to ferns, to their primitive flowerless beauty, their diversity of foliar textures and shades of greenness, to their range of sizes from tiny to towering. And I want to invite some to come live with me and my begonias and Clivia and other houseplants, but which ones will be the best match for our house, I wonder, maidenhair or staghorn or bird’s nest or …? I asked the author of “The Complete Book of Ferns,” a new book on ferns, both indoors and out.

Mobee Weinstein is foreman of gardeners for outdoor gardens at New York Botanical Garden in New York City. She’s taught classes in indoor plants at the State University of New York and at NYBG. And she is also the person who first introduced me to many of what have become my favorite houseplants, back when I was a beginning garden writer, and I’d visit her in the NYBG greenhouses while working on a story—some really special times.

Mobee shared her list of top indoor ferns to try (including tuber fern, Nephrolepis cordifolia, seen beside her in the photo below); some fern sources; and even some key fern-care advice, like how to water properly.

Read along as you listen to the January 27, 2020 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Spotify or Stitcher (and browse my archive of podcasts here).

Plus: Enter to win a copy of the new book, by commenting in the box at the very bottom of the page.

‘the complete books of ferns,’ with mobee weinstein



Margaret Roach: So welcome, Mobee, so good to have you and think of some of the fun times we’ve had before. So many plants I associate with you, it’s funny, from classes and from interviews and so forth.

So anyway, the new book, it’s called “The Complete Book of Ferns,” and it is—from their history and biology and care and varieties for both indoors and out. But this being winter, I thought we’d sort of do an indoor-focused segment. But first, let’s start with a definition. What do I have to do to be a fern? What’s a fern?

Mobee Weinstein: Well, so ferns are plants, of course.

Margaret: [Laughter.] Good, you got that answer right.

Mobee: But most people would think that if something is delicate and lacy, they think, “Oh, that’s a fern.” For example, asparagus fern, which is not a fern at all, and actually an asparagus. But what by definition a fern is, is a plant that is vascular—in other words, it has a system that’s kind of like our veins and arteries. It has a pumping system through the plant.

They also have leaves, but in particular we call these leaves megaphylls, that’s the technical term. And it really just means that they have branching veins, and it allows them to get much larger, having a branched vein system.

And then, they reproduce by spore, not by seed. So that’s what makes a fern a fern. And it really has nothing to do with how it looks to us superficially.

Margaret: And they do look quite different. I mean, in the book, that was one of the most fun… Kind of looking through the glossary of the indoor and then the outdoor varieties that you recommend, I mean, the diversity is quite startling really.

Mobee: Exactly. Most people think of them as very delicate and lacy and always in kind of moist tropical woods or even temperate forests. But most people don’t realize they can be very large, or very leathery, or completely un-dissected or undivided and strap-shaped, and they can grow in deserts and they can grow in water. And people just don’t realize how diverse they are.

Margaret: It’s funny that you say water, because one fern that I grow every year—I actually order it, mail-order, to put on the top of my two in-ground water gardens to kind of shade the water and keep green algae from growing, string algae from forming and so forth, to deprive the light of water, um, I mean the water of light. [Laughter.] One or the other Mobee, I’m not really sure. And it’s just so beautiful. I say uh-zo-la? Or A-zo-la? I’m not sure.

Mobee: Uh-zo-la [Azolla, photo above].

Margaret: Azolla. And I just love it, and it’s velvety and it sort of sometimes picks up a reddish cast at certain times of year, in certain amounts of light I would guess. And it’s just beautiful. It’s like a velvet carpet or something on the surface of the water, and it’s a fern. It’s crazy.

Mobee: It is a fern. And most people would never look at that and think they’re looking at a fern. Even if you look at it close up, you still wouldn’t think it’s a fern, but it is, and it’s rather small. But it just divides and grows so rapidly that it can actually smother water surfaces. So, in tropical areas it’s considered quite aggressive, but they have used it… Well, people learned a long time ago that it helped rice grow. We now know that it’s because it has a special symbiotic relationship. When I first learned it, they said it was a blue-green algae, and now it’s classified as a cyanobacterium, but it’s the same organism and it fixes Nitrogen. So it really helps the yield of the rice crops.

Margaret: Oh, wow.

Mobee: So it’s actually a very important plant for some very important food production. And it’s a little fern.

Margaret: Yes, yes. It’s beautiful. It’d be beautiful in a dish garden even, you know, a little water dish garden?

Mobee: Yes. A little bowl, just a little bowl of water with some Azolla floating in it. They call it mosquito fern because, just as you were saying, you might use it to block the sun out of the water to reduce algae from growing. Because it smothers the surface, it can kind of make it more difficult for mosquitoes to breed in the water. They like open sitting water.

Margaret: Yes. So, ferns for deserts, ferns for water, ferns for lots of different habitats, including our houses. [Laughter.]

Mobee: Exactly.

Margaret: So they’re not one size fits all. And of course, our indoor environments aren’t homogeneous either—no two places inside a house, light exposure or temperature or whatever, and no two houses. So, I don’t know, how could we kind of do this? Do we talk about plants by the types of exposure and conditions they like? Or how do you want to introduce us to some of your favorites or some that you want to recommend that we give a look to?

Mobee: Yes, there isn’t one way that it could only be done. But I like to—and this also goes for outdoors, anytime you want to grow a plant, but indoors it can often be much more challenging—I like to first look at your setting to see what you have. Because it’s human nature to go and buy a plant because you like it, and then you come home and find that you have no place for it, or you don’t have any right conditions for it. We all do it. We do it again and again and again.

But if you can avoid that, you’ll have much better luck. So if you look and you say, “O.K., I have an east-facing window,” you could grow almost any indoor fern from the light needs. Then you have to look at your temperature, how warm or how cool. Most indoors are not freezing, where people are living. But some people do definitely turn their heat down or have rooms or sections of their homes which are cooler, and that could actually be helpful. But mostly we’d say they’re at least 60 but 70, 65-70 degrees, at least in wintertime. And in summertime, if you don’t have air conditioning, it’s much more. I know my apartment can get up to 90 or more in the hot summer days when the AC is off. [Laughter.]

Margaret: Right. And I have two mudrooms, little mudrooms off the house. And some people might have a sunroom, a porch that’s enclosed and maybe they don’t go out there and sit all day in the winter. But it is still an environment that might suit some types of plants and not others. And so you really have to evaluate each spot. So an east window is a good one. What about some of the… So not the brighter-light windows.

Mobee: So east would be, in my opinion, kind of our second lightest. North is the lowest. And some people will say you can grow many ferns in north light. I actually have eastern and south, but my south is not really usable. So most of my plants in my apartment are east-facing. And that is working beautifully for a lot of these. Of course, I wouldn’t grow some other plants that need a lot of sun to bloom, etc. But all the plants I have can take the east light fabulously.

And I winter over limes and things like that in the east light. So that’s pretty good.

West can be O.K. for a lot of the ferns, but especially in summer, it can get a little too hot. So you just have to be careful. And south is the same thing. South is the most light, the strongest light. But again, in the summer it could be way too strong and way too hot for most of the ferns. So you’d either back them away from the window, or have a sheer curtain or something, or you could move them to the south exposure in the wintertime to get more light if you felt that worked for you.

Margaret: Right. And my houseplants all get evicted and go out into the garden in the summer, so… [Laughter.]

Mobee: Right. I have a small terrace; they don’t all go out there, but some of them do. And then they’re much happier. But they’re still facing east, they’re just outside. But that’s an enormous difference, as you know. Just moving inside the window changes a lot.

Margaret: And then I would imagine that scale, like how big, I mean some plants don’t suit us because we don’t have enough room. Do you know what I mean? Sometimes we need something that’s more miniature-ish compared to a big thing. I mean that’s the other thing I think to consider, is how big. It may be we’re buying it in a 3-inch pot if we’re mail-ordering it, but it’s not necessarily going to stay that size. So, I guess we need to know that too, don’t we?

Mobee: Right. So, I mean there are some really large ones which are great for atria or indoor landscapes, or if you happen to have that kind of space in your home, you could get a tree fern, even if it was small, it could get larger for you. Or you could grow some really big baskets of staghorn ferns or some of the other basket ferns. But they might not start out that big, but ultimately they could get that big for you and you would want a big piece. But a lot of us don’t have quite that room, so there are some that can be really happy in a 4- or 6-inch pot for basically their whole life, other than occasional repotting or refreshing; they wouldn’t need a bigger space. So, that’s also helpful for a lot of home gardeners.

Margaret: Yes. Now, you’ve been around plants your whole adult life [laughter], you know a lot about plants, you probably can hear what they’re saying. But can you tell maybe by looking at an assortment of ferns, what conditions they’re for? In other words, some have almost like a plastick-y,thick strap, like you mentioned, leaves. Like the bird’s nest, the Asplenium, versus the delicate, feathery, tiny little leaflets of maidenhair. Can you infer from that, what kind… Does that give you any clues as an expert?

Mobee: It definitely gives us all clues. You can’t always be 100 percent certain unless you know what the plant is. But in general from its texture, you can tell that it should be able to tolerate less humidity, or that it would need more humidity. So a maidenhair, which is one of the most popular because they have some of the most delicate, finely cut foliage, and they come in all kinds—there’s hundreds of varieties of them. They have very small leaflets, a lot of those, and very, very thin in texture.

When you see something like that, it’s telling you, “I generally need a lot of humidity because I’m not protected from drying out.” Whereas when you see a thick bird’s nest frond, or the crocodile fern frond, that are thicker and like you said, almost plastic or leathery. And they have that kind of structure and texture, that thick texture to them—those are generally going to be much more tolerant of dry air because they’re not so exposed. They already have a thick coating on them and a thick texture to them to help protect them.

Margaret: Right. Did I say the wrong genus when I just said bird’s nest or did I say the right thing? Are the bird’s nests Asplenium? [Bird’s nest fern, Asplenium antiquum, above from Wikimedia.]

Mobee: Yes, yes.

Margaret: They are. And what are the maidenhairs? They’re in which genus?

Mobee: Maidenhairs are Adiantum.

Margaret: Right, of course. Adiantum. So you can infer, O.K. Because I kind of think that about plants in general, but you know, I didn’t know. So if we wanted to have the best shot at success, we’re going to do a little analysis of the conditions first and the space and so forth. And then we’re going to go plant shopping.

If I want to get started with some ferns, are there some that you feel that are not only beautiful, but are really doers, you know—that you would like to see people try and have success with? Or some that you wouldn’t be without?

Mobee: There definitely are. And I mean, there are certainly quite a number of them. It’s not limited to one or two. Ferns can be finicky and they can sometimes get a bad reputation, because if you get a maidenhair and you don’t know how to take care of it and it dries and dies on you, then you think, well ferns are like that. And they’re not. So there’s quite a number of them.

I have a lot of favorites, of course. I like all ferns. [Laughter.] Some are much easier to get and some are a little harder to get, but there is a type of bird’s nest, the common name is Japanese bird’s nest, and it’s Asplenium antiquum. But that species is smaller and narrower leaves, and can be kind of containerized and kept more compact, easier, and for longer times. And I find it to be really one of the best, and really handsome. And there are varieties that have very crested tips. There’s one that’s really crested, it’s called ‘Leslie,’ and there’s one that’s lightly crested and it’s called ‘Crissie.’ So you could get a plain strap leaf, or one that’s just very wavy on the edges, or ones that have this great cresting, and they’re really pretty tough. I like them a lot.

Margaret: So the Japanese bird’s nest? O.K., Japanese bird’s nest and its varieties.

Mobee: Right. Also, what a lot of people just call Boston fern, that’s actually a species whose botanical name is Nephrolepis exaltata, and those are pretty good for the home. I actually have a big one of those, which is a variety called ‘Tiger,’ which has nice striping in it. And that’s one of my favorites, as well as some of the miniatures. But those can be a little trickier.

But there’s a closely related species, that’s Nephrolepis cordifolia, and its common name is tuber fern, or tuber sword fern. It makes little tubers in the soil along the stolons and stuff that run through the soil. So that one is really durable, it’s upright, it’s handsome, it’s very common as a landscape plant in any tropical or subtropical area. But it makes a great indoor fern as well. It’s just really tough. And there’s a very popular variety of it that’s smaller, and that’s ‘Lemon Buttons,’ and that’s one of my favorites and that is really easy. [Above, Nephrolepis cordifolia; Wikimedia photo. Also in photo with Mobee up top.]

Margaret: And these are very different looking, I’m imagining. Yes, these are all very different looking.

Mobee: Actually, I like to mix them together, too, in dish gardens, because they make a great combination, you know, for interest. So those are some of my real top favorites. But there’s, I mean, I could probably rattle off a dozen or so depending on how many you want to hear about. Or how much time you have. [Laughter.]

Margaret: Tell us a couple more that are on your top list, and then we’re going to talk about some cultural stuff and so forth.

Mobee: So there’s a group, a general group, they’re botanically called Pteris, and there’s a P in front of the T there, it’s silent. And Pteris is actually Greek for fern, and these are called brake ferns.

Margaret: B-R-A-K-E?

Mobee: Right. And there’s a number of different species, but there are a few that are really common. And the Cretan brake fern [detail above] is probably the most common with the most varieties, and those will grow nicely. So some of them are variegated, some of them are more finely cut, they’re interesting.

And then there’s two other species. One is nipponica [below, Wikimedia photo], which is one of the most common, and it’s got a nice creamy white variegation on it. So it’s very, very popular. It’s often mislabeled or identified as a Pteris cretica ‘Albolineata,’ but it’s not that. But if you see that name, it’s probably that fern just incorrectly labeled.

And then one that’s silvery, much more silvery than creamy white. And those are either silver lace fern by common name, or the Victorian lace fern. Those are Pteris ensiformis, and they’re just two different cultivars. And they look very similar, but they have a nice silvery combination with the green, so you can get some really nice coloring going in there and texture. And those are really pretty tough. So that’s another top one.

The rabbit’s foot group, those are nice and they’re fun, and they’re pretty easy. And they have nice creeping rhizomes. So one has more of a whitish rhizome and that’s the white rabbit’s foot. You’ll get lots of common names on these, so it’s not always easy to do it by common name. And then another one that’s often called rabbit’s foot or squirrel’s foot, and that has more of a brown rhizome and they’re fuzzy rhizomes. [Below, squirrel’s foot fern detail, Davallia mariesii var. stenolepis.]

Margaret: There’s a great picture in the book, I remember one in particular, a really fuzzy one. It looks like an animal. [Laughter.]

Mobee: You do, you want to pet it, you totally want to pet it and you can’t think this is a plant? It looks more like some creature.

Margaret: Yes. So I love in the book how you took the time to really explain things that might sound simple, but are kind of off-putting, especially to the beginner who’s adopted a plant and doesn’t want to harm it, doesn’t want it to die. And stuff like watering, because it confounds people, you know? How much, how often, applied how? If it’s in a pot, do I dunk the pot, do I pour water through it? How often, and if it’s mounted on a board? So basics, a real quick sort of a minute course in watering. I mean is there general wisdom?

Mobee: Well, probably if you had to limit it, it would be the most single important factor. And most plants are killed due to watering, either overwatering, which is usually what people do indoors, or with containers. Or underwatering, which they often do outside. But overwatering is clearly our biggest problem.

It’s hard; every plant has a different need to begin with. So that’s why you want to know what your plant is and try and find out what does it like to begin with. And then you have to look at your soil, your container, what time of year is it? Is the plant in a resting phase or should it be actively growing? How much sun is it getting, or light? How warm is it? How dry is it? So, those are already confounding for a lot of people who don’t have experience.

And so, you want to just at least start to be aware of these things, and then you have to start checking the water. So the idea is not to water a little bit every day. You want to water thoroughly and then wait. You can always check the soil surface with your finger to see if it’s moist, or wet, or very dry. If it’s a plant that you have in your house every day, you can start to also pick it up and get a feel for how heavy it is when it’s wet, because you’ve just watered it and you know that it’s soaking wet. Or how light it is when it’s dry and you pick it up and you say, “Uh oh.” [Laughter.]

Margaret: “I went too far!”

Mobee: “I better get this some water right away. No wonder it’s starting to wilt.” You know? So checking the soil of course is best but, feeling, looking for the weight, or sometimes with clay pots you can tap on them and see if they’re moist or wet. But the best is to really touch the soil and then get a feel for how heavy it might be, and then water it thoroughly. That’s why you want drainage holes, so the excess can come out. And if you have a saucer underneath, which is usually nice, if the water sits in there for half an hour or an hour, probably time to dump it out, so it doesn’t sit waterlogged.

Margaret: Right. So let the soil really take up, percolate up, some of that moisture, but then don’t let it stand in it for a day or two, or three or four. Yes.

Mobee: Right. Unless it’s an aquatic, then that’s what you’d want to do.

Margaret: [Laughter.] Yes. So you know, I looked at the book and I’m going through the pages, and I want all the ferns, and some of them I don’t know where I’m going to get them. And the local garden center in my area has more and more houseplants, because houseplants are kind of a thing again.

Mobee: Exactly.

Margaret: They’re coming around the mountain again, which is great. And so I’m seeing more diversity than I used to, but still, are there other… I mean like Logees.com for instance is one place I know that you can order things. Are there places that you know of where people should be looking for ferns?

Mobee: There are a few. And I know that on eBay and other places they’re selling them, I just haven’t bought from them, so I don’t know what I could recommend.

Margaret: I understand.

Mobee: But I know if you start searching sites like that, you’ll find stuff and maybe then you can see if people are saying they have good recommendations. But Fancy Fronds, which is out in Washington, which is great.

Margaret: She’s great.

Mobee: Which is Judith Jones’s nursery, is a great mail order. Hers tend to be more temperate outdoor plants, but she does have some that are perfectly at home indoors. And she’s certainly very knowledgeable and reputable, a wonderful person. So that’s one potential. For more tropical ones that you would grow indoors or only outside if you were in the tropics, there’s Glasshouse Works-

Margaret: Yes, Glasshouse Works.

Mobee: …which is in Stewart, Ohio.

Margaret: Yes, of course.

Mobee: And typically, they’re going to send you very small stuff. But that’s O.K. All mail-order is pretty much small. Logee’s is a fabulous place; they do mail order and I go there, but they don’t have very many ferns.

Margaret: No, just a few.

Mobee: They’re very limited on ferns. Staghorns, they seem to sell, but unfortunately I wish they would grow more ferns. I’d like more sources for it.

Margaret: I wish we had more time; I would throw in Plant Delights, which has a big collection of ferns.

Mobee: That was the last one I was going to add…

Margaret: Yes, yes.

Mobee: … because they overlap.

Margaret: Good. Thank you so much and I hope you’ll come back and talk about outdoor ferns when we’re a little closer to spring, Mobee, and thank you.

Mobee: I would love to.

Margaret: The book is “The Complete Book of Ferns,” and we’ll talk again soon. Thank you.

Mobee: Thank you so much.

more of my conversations about ferns

(Photo credits: Mobee portrait, by Christina Bohn Photography; Azolla, rabbit’s foot fern and Cretan brake fern photos, each in the book, from Shutterstock; others from Wikimedia as noted.)

enter to win ‘the complete book of ferns’

I’LL BUY A COPY of “The Complete Book of Ferns” by Mobee Weinstein for one lucky reader. All you have to do to enter is comment in the box at the very bottom of the page, answering this question:

Do you grow any ferns (indoors, or even out)? (I have many species outside, from Japanese painted to ostrich and more, but using Mobee’s suggestions, I want to start an indoor collection now, too.)

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, January 29, 2020. Good luck to all.

(Disclosure: As an Amazon Associate I earn from qualifying purchases.)

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 10th year in March 2019. 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 January 27, 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).

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