EVERY YEAR when I get to the sweet pea listings in the seed catalogs, I think: This is the year, the year I’ll organize some supports in the garden for them, and indulge in their unmatched extravagance of color and fragrance.
Matt Mattus doesn’t hesitate one second, or have to think twice about sweet peas ever. They are always on the list in his Massachusetts garden, grown both as cut flowers and elements of beds and borders.
Matt, author of “Mastering the Art of Flower Gardening” (affiliate link) and also of “Mastering the Art of Vegetable Gardening,” gardens at his Worcester, Mass., home. Matt is the third generation of his family to live and garden there, in the same house with its two-acre landscape. He’s had a career as a graphic artist and toy designer at Hasbro for many years, but for at least as long he’s been passionately designing garden scenes and experimenting with one genus or another in his garden and greenhouse, where he can’t resist the impulse to try every last species or variety of something that he can get his hands on.
Read along as you listen to the Jan. 8, 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).
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growing sweet peas, with matt mattus
Margaret Roach: So Matt, we should warn people though that they may have a seed-catalog or a plant-catalog shopping binge if they listen to you [laughter]. How are you?
Matt Mattus: I’m great. You make me sound like… I guess I’m more obsessed than that even. But we know we’re not alone, right?
Margaret: No. And from your Instagram, your popular Instagram feed, I see your fun experiments and so forth. In a “New York Times” garden column we did recently about a range of annual vines, I introduced you as a person with “a trial gardener’s mind,” because besides having that strong design sense I was just speaking about, you also love to try a group of plants or a genus of plants, hands-on yourself, right?
Matt: Right. I think maybe that’s the artist in me, that idea of having a Crayola box of crayons with all those colors, and curiosity. I want to see and appreciate all those different nuances within a genus, or even within a species. So something like zinnias or sweet peas, or especially with annual flowers, you can grow 10, 15, 20 varieties, side by side, and that’s always interesting to see that at botanic gardens. So I try to do that here.
Margaret: Yeah, I mean it’s interesting because the descriptions do their best to say the distinctions from one to the next, but it’s not the same as trying it. Plus there’s the variability, or the variable, rather, of “this is my place and this is my conditions,” and this one might do better for me than that one, and so on. I mean, there’s that, too, right?
Matt: I think with most annual flowers you see those differences, right? With morphology, you see the different forms and shapes. Some are short, some are tall, some of them have different flower sizes. But with sweet peas, the differences I think are mostly with color. I mean, they have a really wide range of color, and they’re all beautiful colors.
Matt: Salpiglossis, I know. Right.
Margaret: [Laughter.] Do we even grow that? Does anyone even grow Salpiglossis? How many did you try?
Matt: I don’t think anyone grows it anymore. I think sometimes it’s one of those lost, forgotten, old-fashioned flowers. But I found an old book, it was just from the 1930s, but it was in an estate gardener’s book And I saw that Salpiglossis was grown as a greenhouse plant, so they would grow annuals in the spring and summer in greenhouses in England for display in conservatories. So it’s fun to look at those old books and see maybe that’s how I could grow some of these. So yeah, I do those experiments, too.
Margaret: Yeah. So with the sweet peas, as you explained to me when we did the Times story, you kind of group them into roughly two categories. And I am not trying to say this is the official lineup or whatever. But you sort of talked to me about the antique types with somewhat smaller flowers and these larger-flowered Spencer types, and how you grow and then also use them differently in your garden. So maybe help us a little bit with that, because I don’t think many of us who are first-timers especially or may have only tried one or two sweet peas know the wide world of it as much.
Matt: I think even among flower farmers or anyone who’s grown sweet peas who’ve gone to, let’s say, a website that specializes just in sweet pea seed, I think everyone’s confused with the old classifications. There were like multifloras and grandifloras. I’ve even asked my plant-breeder friends like, “What does that mean?” Those are really old-fashioned classification terms for a lot of flowers.
But I mean, basically in the world of sweet peas, grandifloras are anything sort of before 1907 or 1901, depending on where you look. That’s when the Spencer varieties, which maybe people have seen those listed, the Spencer varieties were developed in England, and those were a larger cut-flower type, long stems, big flowers. Those let’s say 1905, 1907, that happened. But before that would have been your grandifloras and multifloras, and those are just old-fashioned terms. Multiflora officially means there’s more than four flowers on a stem, but I don’t think any of us care about that.
I try to think of them as old-fashioned… Just two groups: old-fashion[ and then Spencers in our modern world.
Margaret: You use them differently. You create different supports for them and your end product, so to speak, your desire of what they’re going to do for you is different. And how do you use those two types?
Matt: Well, my history of sweet peas goes back to the 1980s. Right out of college, I joined the Sweet Pea Society in England.
Margaret: The Sweet Pea Society? [Laughter.] I had no idea. You forgot to tell me that when we were doing the Times story. The Sweet Pea Society!
Matt: There is. You could still join the Sweet Pea Society in England. But that’s a great source, a resource for sources in England. And for a long time, the good sweet pea varieties could only be bought from England, especially in the 1980s and 1990s.
Now in the U.S. we have far better sources, but I still order some from England, too. But the Sweet Pea Society would hold flower shows through the 20th century. And I don’t think they’re as popular as they once were, but that always appealed to me, exhibiting; growing for exhibition. And sweet peas, like dahlias, are one of those plants that was grown for exhibition in England mostly.
So that appealed to me, and I don’t expect people here to do that, but you could. I mean, you could grow them in these very strict ways where you limit them to one stem tied to a bamboo cane. They call it the cordon method. It restricts their growth. So you could get an 18-inch flower stem with a 2-inch flower on it.
Matt: I liked doing that. It’s fiddly, it’s fun to do, and you can easily go online and find out how to do that. I still grow some in that way with these nice, tidy rows of bamboo canes that are 8 or 10 feet tall [above], and I plant seedlings on those and train them. But I also like to grow them in the flower garden on teepees or on towers of branches, or various structures like netting.
Margaret: So with the cordon method or growing them on the bamboos, you make this support structure for them and you tie them up every so often so that they really… I mean, these are not like morning glories. These are not twining vines. These need your help. They hold on by tendrils, yes? Little delicate tendrils.
Matt: Right. You’ve grown edible sweet peas. Right?
Margaret: Sure. Sure.
Matt: So they have those little swirly grape tendrils that grab on. So that gives us a hint on how to grow them. So if you want to be fiddly, and you want to train a sweet pea plant for the most extraordinary flowers, you could limit them by training them on a cordon or a bamboo cane, but you would have to tie them. So you mentioned tying them with a string [above]. I have to do it every three or four days in May and June. That’s how fast they grow.
Margaret: To get these long-stemmed, larger ones, for the cut-flower use. Yes?
Matt: Right. For that method, if you restrict all the side growth and you’re cutting the tendrils off so they don’t grab the flower buds next to them. The leaves get really big. They’re as big as the palm of my hand. It’s kind of magical. So it’s fun to have some that way. Especially the old-fashioned varieties, which have shorter flower stems, I think they’re best just grown on twigs or branches, like pea brush like you would grow garden peas basically, except no, they’re going to grow a lot taller. These are going to grow taller than your garden peas.
Margaret: Yeah. You showed me a picture that I think you said it was inspired by a clematis growing in an English garden that you had seen. It was almost like this kind of, they’d taken twiggy pea brush and they’d kind of made it almost like a ball of it. They’d bent it; they’d put it in the ground on one side and then bent it over and put it in the ground on the other side and done the same in another direction. So made this dome and you let the old-fashioned, the antique varieties scramble over it.
Matt: Yeah. I think with a lot of vines you could do that. I mean, I use branches from our birch trees or the trimmings from our hornbeams, which to be honest, I might trim every other year, so they’re pretty long. So in the spring, I make a dome in the garden, and it could be any height you want. I mean, ours end up being maybe 5 feet tall, 4 feet tall, and it’s fun to make these. We want those craft projects in the spring. Right?
So in the wild, the Lathyrus odoratus, the sweet pea, grows on shrubs. So this would be like you’re mimicking it tumbling over a shrub. I mean, Clematis grow that way, too. [A twiggy dome at Matt’s with sweet peas just getting started beneath it.]
Margaret: Right, and so the ones that you’re looking to train onto those bamboo canes that cordon method: Those are the Spencer types, and those are the ones that you’re turning into those cut flowers and managing it for the longer stems and the bigger flowers and so forth.
But in both cases, wherever we’re going to use in the garden, you start them… I mean, we all know peas, edible peas, are one of the earliest things that we can put out; they’re cool-season adaptable, or they love the cool season. So do you start them in the greenhouse, or can we do them under lights for those of us who don’t have a greenhouse? Or do you direct sow them? What do you do with sweet peas about when?
Matt: I have a greenhouse, so I keep it cool. It’s a cool greenhouse [above, and in background of garden shot, below], meaning it’s just… I keep it above freezing, but below 45 at night, and that’s just what sweet pea wants. I think that’s the biggest confusion with people starting sweet peas. You’ll see them online starting them under lights, indoors, and that’s not what they want. Think of garden peas, right? When you sow your peas, we always sow them in March, or as soon as the ground can be worked. Right?
And it’s the same with sweet peas. The trick with sweet pea is first of all, it’s probably different for every state in the country. So you have to find your own little window of when you can plant them, but here’s what they want: They want cool or cold weather. If it’s above 20, you can sow them. If you’re in Washington State or you’re in zone 7, let’s say 7 to 10, you could sow them in the fall and they’re going to do just root growth.
There are even Cornell studies in, I think around 1910, where they would sow them in New England in the fall. And I tried that under hay, and they did grow. I mean, they blew the week earlier in June [laughter].
Margaret: So no big headstart, huh?
Matt: No. I mean they produce better roots, but it gives us some tips of what they want.
Margaret: So I am not going to treat them like I’m treating my tomato seeds inside.
Margaret: If I am going to do them inside under lights because I don’t have a greenhouse like you do. I would want to pick a cool room and I would want to make sure that… I mean a lot of the newer lights give off less heat, which is great in this case, right, and that they’re not right up against them. I mean, I think we could start them indoors, but we have to be careful not to let them stretch out from too little light and too much warmth. Is that the idea?
Matt: Yeah, exactly. I think sweet peas are of one of those plants, they’re sort of opposite of tomatoes. I mean, you nailed it. If you have a garage or you have a sunroom…
Margaret: That’s what I was just thinking about, a sunroom kind of thing. Yeah.
Matt: Yeah. But a light unit in it. I mean, they love, they want really bright light. So if they want really bright light and really cool temperatures, and you can start them as early as November if you want, if have that condition. If you can keep them at 35 all winter, they’re growing their roots. That’s what a lot of flower farmers do. They sow them November, December, January. They want to bulk up at these cold temperatures, so they keep them at 35 to 45, but under really bright light, and that means either in their hoophouse or under artificial lights.
So it’s not really where any other plants we would grow. But if you do have a garage that’s unheated, but it hovers around freezing, you could plant your sweet peas right now.
Margaret: And the other thing is you can also start right around six or so weeks ahead of your set-out date. I assume in our area, where the last frost date is sometime in mid-May or so, that the set out date a few weeks before that, the transplant date?
Matt: The alternative is… I mean, so there are many ways to grow sweet peas. So on the easy side, you could plant them just like you do your garden peas.
Margaret: Direct sow, right?
Matt: Yeah. So you could do that. I think the difference—the benefit of starting them earlier and cold—is that they bulk up more roots and they might form more side shoots, and it’s those side shoots that are stronger-growing or more vigorous than that main shoot. Why you often see pinching—we always pinch sweet peas—but growers could either keep all the side shoots or remove all but one side shoot. But rarely does anyone keep the main shoot.
Margaret: Oh. Huh.
Matt: So it gives you a much stronger stem. With sweet peas, it’s all about the roots, right? So you might see people growing them in toilet paper tubes, which is O.K. if you have that many toilet paper tubes, but they want that deep root run. So a deep pot is better, a root trainer or a deep cell [above]. I mean, you can grow them in 4-inch pots if you want to, but you’ll notice all the roots are at the bottom.
Margaret: That’s a good point is that they do, compared to a lettuce seedling or something, that they don’t want that tiny little cell that’s not very deep.
Matt: You know what’s interesting, too, and I’m trying this year: Some flower farmers are sowing sweet peas in combination pots, like a 4-inch pot that’s deep, but like 25 seeds in a pot and planting in winter and keeping them cold. So they grow very slow or hardly grow at all in the winter, but they’re forming roots. But they transplant really easily. You can separate them. The roots are very strong.
And you can separate them so it takes up less space. So let’s say you don’t have a lot of space, but you want a cut-flower garden, you plant 25 four-inch pots early in the year and keep them in your garage under lights. And then they’re just barely growing, but they’re forming a lot of strong roots and a lot of leaves that are closer together and dense. And then separate them, let’s say, in March into individual pots, and then gradually introduce them outdoors.
Margaret: Do you have a couple of favorites, both of the antique types that I might let scramble up a twiggy support. If I’m just getting started with sweet peas, I might do that, and I might just even direct sow them or sow them a month and a half or so ahead indoors in a cool, bright spot and transplant them around a twiggy structure or something, or on some netting. Do you have some favorite old-fashioned varieties, the antiques like that, that you recommend?
And also if I wanted to try training the larger-flowered Spencer types, do you have any favorites of those that we should be on the lookout for?
Matt: Yeah, sure. I think if you like fragrance and don’t mind having smaller flowers, but lots of them, I think there’s a variety called ‘Matucana,’ which is, it’s like an improved selection of the original wild sweet pea. I mean, no one really knows even what the wild one was [laughter], but that’s probably the closest you can get. There’s some notes that say it was grown back in the 1700s, but super fragrant. So that’s a purple and maroon bicolor, both small flower, maybe a half-inch wide, but that scent will waft across your garden.
So that’s something I grow every year. I try to keep that in the garden garden, but not as a… I mean, you could use it as a cut flower, but you’d have to cut the whole stem. But I like the colors of sweet peas, because they just have the most beautiful range. Personally, I think with the watermelon colors, the cotton candy colors, there’s a lot of periwinkle purples, pinks. I try to keep them into two groups. I grow all the periwinkle blues and pinks as one, and then I grow the warmer colors like cerise and watermelon and coral. I just don’t like the dark red ones. Personally, they seem to not fit in.
Margaret: Yeah, they’re different from either group that you just mentioned.
Matt: The color. Right?
Margaret: Yeah, they’re different. Yeah.
Matt: And then they were flakes and stripes, which were really old-fashioned. They were popular in the turn of the century. Sweet peas were the most popular cut flower in 1900.
Margaret: And you said flakes, so they’re almost like they’re speckled or not variegated exactly. But it’s a mottled flower. Yeah?
Matt: Right. It’s like a red and white stripe, sort of; orange and white stripe. There’s no ruless. But I liked those old-fashioned ones.
Margaret: And now you mentioned pinching. So just real quick, I wanted to ask, so I’ve got these seedlings. Let’s say, I started them indoors, and I’m pinching out what the second set of leaves or which set of leaves that forms. When am I pinching it?
Matt: Yeah, so second or third. If you’re growing them under really bright lights, so let’s say you do have in the garage and they’re between 25 and 40, your leaves are closer together, but they form these two pairs of leaves. I usually take the second pair out. I leave just one pair of leaves. What you don’t want is long, spindly plants that are grown warm under lights that you never pinched, because those really… They probably will grow 24 inches long and may not even bloom.
Margaret: Right. So you want a really sturdy plant. In a way it’s counterintuitive, because you think, oh, I’m letting it grow longer. But actually what it’s doing is it’s stretching out, it’s weakening. It’s not going to reach its full size by letting it…
Matt: Yeah. And I think if you do by accident, grow them warm and they’re long and lanky, definitely pinch them back. Leave like 3 inches of that spindly stem and hope that stronger side… Don’t be afraid to pinch. That’s big takeaway here.
Margaret: All right. So: I want to say it’s catalog season [laughter], and you’re a good shopper. I want to ask a couple of sources or a few sources where to get sweet pea seed, because I know Select Seeds, for instance, has, I don’t know, around 20 varieties or something. I don’t know if you’ve ever ordered from Swallowtail Garden Seeds. I see they have a lot.
Matt: Yeah. Renee’s Garden.
Margaret: So I don’t know about your couple of others. Renee’s, O.K.
Matt: Yes, Renee’s, and Johnny’s carries some. There’s Floret Flower Farm, of course, that have some great ones, they save their own seeds. There’s a new one, Sweet Pea Gardens from Washington State. I haven’t tried them yet.
Margaret: That’s interesting. I saw that they moved up from California or something, a few years ago.
Matt: I’m going to try them this year. But I also order some from England. I mean, it is always a chance now with Brexit and importation rules; it’s tough sometimes to get seed in. But there’s Keith Hammett, a New Zealand breeder who sells online. And those are the top. There’s like three top sweet pea breeders, so definitely Keith Hammett is up there. And there’s Owl’s Acre, which is a really good one. Roger Parsons, I definitely… I probably ordered most of mine from Roger Parsons in England.
Margaret: To digress from sweet peas: Is there something, because you seem like with this trial gardener’s mind, as we said at the beginning, you’re a person who likes to know for yourself if in a group of plants, is this one’s the best or that one’s the best for you. Is there some sort of holy grail item you’re on the lookout for this year; is there something new that you’re thinking of jumping into? Or are you continuing a trial that you’ve done in previous years? I mean, what’s Matt Mattus got us eye on right now? Tell us the next thing. [Laughter.]
Matt: It’s always a long list. I’m curious about Mimulus, the monkey flowers.
Matt: Yeah, I know there’s a lot of breeding going on at University of Connecticut and there’s a few, if you just Google, “new breeding Mimulus.” You’ll see the colors and crosses and inter-specifics, even intergenerics, two different genuses crossed together. I’m curious about those. The past few years I’ve been starting those. So I think I’m curious about those. And if you’re at a garden center look for Mimulus; you’ll see them. There might be some Proven Winners ones, or different selections from some of the big brand names that you’re starting to see. And you might not know what they are, but try them.
Margaret: So monkey flowers, O.K. So that’s one thing that you’re on the lookout for.
Matt: Yeah. Nemesia. There’s a lot of breeding going on with those. These are all sort of cool-weather annuals you would see sold with pansies in the spring.
Margaret: I can’t even remember the common name for that.
Matt: I don’t even know if there is.
Margaret: I don’t know if it even has one. So that’s another one. Yeah. Are all your houseplants inside right now or in the greenhouse, and they’re all…?
Matt: Gosh. Every room is full. Yeah, it’s crazy. Right [laughter]?
Margaret: I know. My fancy-leaf begonias, and I know you have a lot and you kind of use them outdoors as almost like annuals as well in the garden season. Mine are mad at me this year, and I don’t know what it is. I feel like all the plants even know that the weather is upside-down; even indoor plants know that the weather is upside-down. It’s just a weird year. That’s subject for another time.
Matt: Begonias is another thing. I will say, they do pout when they come in.
Margaret: They do. Yeah.
Matt: And just find a room where they could go semi-dormant.
Margaret: Yeah, they want to go back out in the humidity [laughter].
Matt: You can’t blame them. Right?
Margaret: I know. Well, thank you for making time. Matt Mattus, I hope I’ll talk to you again soon. And happy seed catalog shopping meantime [laughter].
Matt: Thank you, Margaret.
(Photos all from Matt Mattus, used with permission.)
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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 Jan. 8, 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).