growing primula from seed, with ken druse

I WAS REMARKING to my friend Ken Druse earlier this spring about a garden I’d just visited, and how the stands of primulas in it made me jealous, and crave more, more, more. But only a few primrose varieties are even sold in local garden centers, and if you really want to create a dramatic swath of the diminutive plants… well, that would add up to quite an investment.

As I was ranting, my text buzzed to alert me there was a message, and there was a photo from Ken of a flat of his just-emerged primula seedlings—hundreds of them, that he’d successfully winter-sown outdoors. All for the price of a couple of seed packets. I asked him how he did it, and about other things you can sow that way.

Ken, who gardens in New Jersey (those are some of his Primula japonica in his canal garden, above), is the author of 20 garden books and also my co-host of the Virtual Garden Club that we put on a few times each year. He’s a master propagator who loves to crack the code of how to make more plants of any kind. He shared the how-to’s of his success with primula seed and more winter-sowing experiments.

Read along as you listen to the May 29, 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 or Stitcher (and browse my archive of podcasts here).

primulas from seed, with ken druse



Margaret Roach: Hi, Ken, how are you?

Ken Druse: Oh, hi, Margaret. Is it spring? Is it summer? Is it winter? I’m a little confused.

Margaret: [Laughter.] I’m not even sure anymore. I give up. Is that a trick question? I guess so.

I said in the introduction that I was jealous when I went to this garden, I saw these just along the edges of beds, not hundreds, but a big strip of them here and there so that it caught your eye, because they’re little plants, generally speaking. So they look good in mass, right? And then when you showed me yours, oh my goodness, what’s going on over there?

Ken: [Laughter.] Mass, that’s a good word for it. Well, we see photographs of drifts and swaths and streams of color, and then you go to buy three plants and it’s $45 plus shipping.

Margaret: Right. Right. Exactly. Exactly [laughter]. Right. If you want 20 or whatever, let alone more, but…

Ken: You need more than 20.

Margaret: Yeah. I find sometimes they self-sow, but they’re not necessarily permanent, you know what I mean? They don’t stay put necessarily.

Anyway, let’s backtrack because we did a class, I don’t know, last fall maybe on winter sowing, and we talked about everything from native wildflowers to other perennials to vegetables even that people could winter sow, and that was really popular. This was kind of an offshoot of that. This is something that you’ve done with perennials before, and you also talked about a little bit in the class. How did you get these things going that you showed me these pots and pots and pots of in flats?

Ken: For years, usually I’d collect my own seed from my own plants and also try something, a packet of seed from Chiltern in England or Barnhaven in France, because it’s not easy to find the primula I want, which are the candelabra primula, and they go up to about 2 feet tall. They’re kind of showy. I usually grow them on the streamside, on the edge of the canal garden where it’s very moist.

But this year, I tried some in a very funny place, at the base of an oak tree, and they’re blooming their heads off. Took two years, which is not very long really for a hardy perennial. But I usually sow them in a flat of sowing medium, which I often cover with a little thin layer of grit. We’ve talked about grit. It’s like coarse sand. Well, it’s chicken grit.

Margaret: Kind of looks like bird-cage gravel, but it’s not. It’s poultry grit that you put out to help them digest their food if you had chicks or whatever, right?

Ken: Right. And then I’d have a flat, and then I’d cover the flat with either an inverted flat from the garden center that’s really open, the kind that has a lot of drainage, kind of a grid, and put a brick on that to hold it in place. Or this year, again, I built a cage out of hardware cloth [above]. And then I put it in a little bit of a shady spot, and that’s it. I did that in January, and then I didn’t even think about it until April.

Margaret: You say cage because Mickey and Chippie and everybody are going to look for seeds, right? Mickey Mouse I mean.

Ken: Probably with primroses they might not, but they disturb stuff. They want to go and bury something in my flat or something.

Margaret: It’s sort of like you’re animal-proofing it, in a sense, like we would do with any winter-sown crop, whether it was in January or later if we were doing our vegetables or something—protect it from the animals. You said in a flat, so you’re just using seed-starting mix and you’re putting it in a flat—it’s an open flat, not individual pots? What’s the deal in there?

Ken: Right. It’s an open flat, but these are all going to be almost the same seed.

Margaret: Oh, so it’s a whole flat of the same variety or species or whatever. O.K.

Ken: Because I had them and I can’t throw them away. I mean, I probably sowed hundreds.

Margaret: Let’s talk about that. I’ll be the psychiatrist. Why can’t you throw them away? No, I’m teasing [laughter]. I can’t either. I just found all these seeds. I don’t know what happened to me last year. Well, we had a droughty year and I ended up giving up on my second sowings of vegetables because it was too tough. I found a few packs of seeds that were a year old then and now are a couple years, and I was so frustrated at myself. I hate to throw anything away or waste anything.

Ken: That’s another show, I guess [laughter].

Margaret: Yeah, yeah. But at any rate, I was just teasing you. It’s an open flat because it was all one kind. But let’s say I want to do a little bit what I call community pots, if I wanted to do four different kinds.

Ken: Right. I do them in 3-1/2 inch pots. I did plenty of that, too. But this year, because of our classes and everything, I tried a couple of different versions of winter sowing. I did the flat with probably at least 200 primula seeds that I collected myself. We can talk about that, too.

And then I grew some things using the milk-jug method [below], which is very popular now. And I’m sure you’ve seen them even though you’re a vegetarian, but they have these rotisserie chickens at all the supermarkets and they come in this container that’s clear on top. It’s got a dome and has a little reservoir in the bottom that’s usually black.

I filled that with medium. Cleaned it, of course. Filled it with medium in that black bottom, and then covered it with the top. I made a lot of holes in the top so rain and snow could drip in. Once you moisten the medium, it pretty much stays moist the whole winter, as it’s not really drying in the wind or the sun. And then lots of drainage holes in the bottom. I also sowed seeds in that.

The jug method we’d have to talk about, but just sowing seeds in that rotisserie container, those were the seeds that sprouted first.

Margaret: Oh, interesting. It was like a little greenhouse that they were in.

Ken: Exactly. It was warm.

Margaret: Right. After.

Ken: These are all hardy plants that need that cold or want the cold.

Margaret: So basically you’re simulating in a protected environment. You’re not even simulating, you’re letting them have the winter they’d have in their natural state, but you’re protecting them from animals and sowing them all in one spot and not having someone dig them up and so on and so forth.

Ken: Right. No lights. No electricity. No watering. No worrying. That is great.

Margaret: Right. This is great for a lot of perennials. And as I said earlier, when we did our, last fall I think it was, when we did our winter-sowing class online—which I bet we’ll do again because it was so popular, it was fun to; great questions and stuff from people that got us both learning a lot more—but this is a great way to start not just native meadow perennials and so forth, which you could collect seed of and then make more, more, more, but also other perennials, non-native and so forth. It’s a great way to start a lot of perennials that need that winter outdoors, but controlling it like this, protecting the seed from animals and just doing it in a more orderly manner.

Ken: Well, it was a massive success [laughter].

Margaret: You said you sometimes collect your own seed as opposed to buying it at Barnhaven or Chiltern, whatever. Your primulas, have they gone by and are you now collecting seed from them…

Ken: No, they’re still blooming. These are the first set that bloom, which are the Japanese primula. They’ll make a whorl of flowers, if you can picture an umbel kind of thing. Then they shoot up a stem from the center of that that goes about 2 or 3 inches and they make another whorl, and then they do it again. They have these tiers of flowers and bloom for probably, depending on the weather, six weeks or so, maybe longer. And then each one of those little flowers turns into a fruit.

People think of fruits, fruits have to be moist. But anything that has a seed is a fruit. I guess corn’s are fruit because those are seeds, too, but we don’t think of that as a fruit. Of course, tomatoes are fruit. These are dry fruits. I guess, if you had a pod with beans or something and it was dry, that’s a fruit.

Margaret: You’d collect those.

Ken: If I don’t do this, I lose them, because they split open and drop their seed. So before they can do that, I cut the whole stem of several plants. And I’ll invert them in a brown paper bag or a paper bag and tie them together perhaps. And then when they split open, the seeds fall into the bottom of the bag. If they’re really green, I put the bag in a place where there’s good air circulation. I actually hang it on a coat rack in an airy place.

Margaret: That’s so funny because that’s what I used to do with a lot of my stuff, too, is I would hang it. I had pegs in my mudroom.

Ken: Actually it’s on pegs, actually.

Margaret: I’d hang the bag from the pegs. I’d put a clip on it or something [laughter].

Ken: I staple some string.

Margaret: Yeah, exactly. That’s funny. I’d walk in the mudroom and I’d be like, yep, there they are, dry; the seeds are drying.

Ken: And then when it’s time, which is late December, you just tip a bag and they’re all there. There’s hundreds. I think each of those fruits must have, I don’t know, 30 or 40 seeds in every single one. There’s really like a thousand seeds, which I don’t need a thousand seeds. And then I try to store them sometimes. If you have to store them, you should store them in the refrigerator [in an airtight jar]. But I put them in an envelope, label it with the date and who they came from. Maybe I’ll separate the colors, because the Japanese ones go from white to dark red.

They’re sort of mixed up. If I have a white one, I’ll put the white one in a bag separately, and I label them, and then I’ll sow them like I did this year. I didn’t know they were all going to come up. They’re all up. They’re the kind of seeds that resent being moved, so I have to learn more about that. They’re all O.K., but I think I should be more patient and let them get bigger before I move them.

Margaret: Just like when we’re sowing lettuce, if we’re doing it and we’re going to prick off or divide the thickly sown whatever it is in our individual pots, for instance, let alone in a big flat, we’re going to divide them and transplant them—you’re going to pot them on to larger containers. You’re not going to put them outside at this tiny little stage.

Ken: Well, they are outside now.

Margaret: The flat is outside. What I meant was into the ground.

Ken: I’ll do what we’re saying, which is to… I’ll get a little 3-1/2-inch pot with medium, and I’ll put four little seedlings in that pot, and that’ll stay outside.

Margaret: Right, but not in the open garden. Not in the open garden.

Ken: Not in the garden yet. Not in the garden soil or anything. And also right away, I wouldn’t put it in the sun, but you don’t have to go through the whole hardening off process because they’ve been outside. You don’t have to worry about wind and even sun to some extent, because that flat never came indoors, n,ever was really warm.

Margaret: Was the cue for when to pot them on four into a little pot, from this big flat of 9 million of them, was the cue… Did they send up some kind of special-looking leaves? Or was there a size, or was it just they were getting crowded? Was there a trigger that you knew?

Ken: Well, I did what I always do, which is I waited for the first true leaves. Because the first leaves that come up, two little leaves come up and they’re seed leaves and they’re usually roundish. And then the next set of leaves resemble what the mature leaves will look like, but they’re very tiny. I moved quite a few of them then and it was not so successful, because I lost quite a bit of them.

They just were too young, too tiny, and they didn’t like it. And since then, I read something from Barnhaven Primroses, which is a nursery in France. They used to send plants, but now they only sell seed to people in the United States, but they said not to move them so young. Now I know, but I didn’t move that many. They’re going to be really crowded and thick. I’ll read some more and maybe I’ll talk to them. Maybe I have to leave them for winter in the flat or something, but I’ll find out.

Margaret: You’re talking about Primula japonica, the Japanese primula. Have you done other primulas or other perennials in this manner?

Ken: I love the Chinese… I guess they might be Himalayan primroses, which are also the candelabra type with the tiers and everything. They bloom later and the colors are so magnificent, but I’ve hardly ever had good luck with them. I’ll have them for two or three years. Something will happen. I think it’s too warm here. It’s not exactly the Himalayas where I am [laughter].

Margaret: No, it’s New Jersey, Ken. You live in New Jersey, not the Himalayas.

Ken: But there’s beesiana and bulleyana. And then the most incredible is a hybrid of those two, which is bulleesiana.

Margaret: I was going to kid you and say, “Is it called something like bulleesiana?” I always thought that was a joke.

Ken: Nope. It’s bulleesiana. Did you ever go to North Hill and see the primroses there? The [former] garden in Vermont?

Margaret: A long time ago. Very long time ago. Yeah.

Ken: They have in Vermont. Okay, Vermont, that’s colder. Their primroses are at the base of a hill. Just like you have a base of a hill, so all the moisture drains down to them and they’re just magnificent.

Primula veris, the common cowslipMargaret: I even like just the basic one. I just like the cowslip. What is that, Primula veris [above], I think or something?

Ken: Yeah, Primula veris.

Margaret: Or oxlip.

Ken: Well, oxlip is a different species. It’s elatior, the oxlip. Veris is the cowslip. I love cowslips. But I’ve heard that they take a long time from seed.

Margaret: Oh, interesting. Interesting.

Ken: You’d think they’re the easiest. You know the ones in the supermarket in March, those little short ones that are sometimes called polyanthus?

Margaret: Yeah.

Ken: A lot of those are hardy, too. I’ve planted some of those and they bloom for months, some of them, and some of them come back year after year, and then they don’t. They’re short-lived. There’s some red ones I’ve had now probably for four or five years. They’re inexpensive. The yellow ones are fragrant. And then if you go to the box store as the flowers are fading, they’d throw them out so you can get them half price before they throw them out [laughter]. But anyway, I digress.

Margaret: You could go to the supermarket. You could get a rotisserie chicken. You could get some primulas. You could then recycle the chicken that when the primulas have seeds, you could make babies of those… O.K., I get it.

Ken: You don’t pot up the chicken and you don’t eat the primula seeds.

Margaret: O.K., good.

Ken: Those primulas seeds are like the size of poppy seeds. They are really microscopic. But the bulleyana, beesiana and x bulleesiana [below, at Ken’s] from Yunnan, China, at elevations of 6,000 to 11,000 feet, sometimes 18,000 feet I think, I try them every year. They come up and I coddle them, and then they bloom in their second or third year, and then they disappear. But the colors are just incredible. I don’t even know how to describe them, just from beige to ruby red to purple, all different colors. But when they bloom, the japonicas, the first ones, are over. They take over.

Margaret: So you could collect some seeds as you have in the past from your own primulas. Are there other things from the spring garden and then the early summer garden that as the season progresses and those things set seed that you have collected and had good success with it where you used this type of a method, this winter sowing, outdoor, no lights kind of thing? Are there other perannial things to winter sow?

Ken: I can’t think of something right offhand, but I like what you said about the meadow plants.

Margaret: Well, definitely, and that’s late-summer and fall collecting and then sowing once it gets cold. Those are classic. A lot of them are pretty easy. That’s great. I’ve done the collecting and drawing in the paper bags and all that with things like my annual poppies and so forth, but I haven’t done a lot of perennials. That’s what I was just curious whether…

Ken: I’ve done done poppies, too, now that you mention it. Some of those sort of meadow plants like Bidens, which is a composite type of like a daisy, and Rudbeckia, things like that. Some of the early spring stuff are either hard… Well, it’s different, because a lot of those really early plants are sown by ants and beetles [laughter]. A lot of them take two years to germinate. It’s a little trickier.

I used to pay so much money for hellebores, and then I would collect the seed, sow the seed in the flat, like we’re talking about. I know they take two years, so I would just leave them just like your Eranthis. It’s almost the same. It’s a little bit tricky, but then they’re sowing themselves under the leaves.

Margaret: Right. To me, it’s easier to let mama plants sow itself alongside itself, and then I pick up the babies and I put them in a seedling flat.

Ken: Well, they’re not quite as precious as some of these primroses.

Margaret: No, no, absolutely.

Ken: I mean, the Japanese ones are beyond precious. They can even be a little bit aggressive. But of course, the ones I want the most are the hardest to grow. I don’t have to baby them, but I have to keep my eye on them because, as I said, they’re precious. Even talking to you, I think I have some new ideas.

Margaret: I mean, what we’re saying is, and we’re using the term winter sowing, and clearly it’s not winter, although we were teasing at the beginning about what the heck season it is since the weather changes every day and we both had a big hard freeze last week and so forth. But basically this is the time to figure out what you do want to do. Because if you want to collect Primula seed or you want to collect whatever, poppy seeds, whatever it is, it’s the time to be looking, keeping an eye out so it doesn’t spread its own seed wherever it feels like it, where you can get it in that paper bag.

It’s also time if you’re going to order from France in England and so forth, or wherever, like from Chiltern Seeds or from Barnhaven Primroses. I think Plant World Seeds, they have different primroses.

Ken: They do. They don’t have bulleesiana, but they have the… Well, they might too, but they have beesiana and bulleyana.

Margaret: There are sources. Go look, see what you want to identify to get, because sometimes things get sold out closer to the time of when they need to be sown, right?

Ken: Right.

Margaret: It’s good to be prepared and to also then plan to get some rotisserie chickens so you can have your equipment [laughter].

Ken: I have my one little rotisserie chicken container.

Margaret: That’s funny.

Ken: By January the seedlings will be out of it, I think.

Margaret: That’s funny.

Ken: We don’t need a whole lot of those.

Margaret: No, no, no. Just in the last few minutes, I mean, I just wonder, anything else that you’re propagating at this time? Is this a time when you do cuttings? Or is there anything else going on, or not this year? Are you doing a lot of dividing?

Ken: I’m doing a lot of air layering.

Margaret: Oh my goodness! What the heck [laughter]?

Ken: I know you know.

Margaret: But with what? What are you air layering, which is a method of propagation? What are you air layering?

Ken: Usually when damages the bark of a woody plant, a slender shoot, if you want to attempt to make more. And then you can take something like sphagnum moss, and you moisten that completely, and you wrap it around this wound that you make. Actually, you can remove the bark and sort of the strip around the whole thing. And then you cover that with the wad of sphagnum moss, and then wrap that in plastic and tie it at the top and tie it at the bottom like one of those candies [above].

Margaret: It’s like a bandage. It’s like a bandage with this padding inside and moisture.

Ken: With a lot of padding. Right. Like a good handful. And then in the case of outdoor woody plants, you forget it. You go away, because it’s going to take probably six months. You could even leave it through the winter.

But there’s a few things around here that people have admired. It’s not easy to propagate woody plants, trees especially. These are trees that you couldn’t even get seed from because they’re very unusual. I’m going to see what happens.

Margaret: You’re trying some air-layering experiments.

Ken: Right. I’m doing with woody hydrangeas, like paniculata. That’ll definitely work. And with a mulberry tree, which will also work. It’s a mulberry that’s variegated and extremely rare, even though it’s not hard to grow. The variegation is just wild. Well, if I can give the plant away that’s very rare, and something happens to mine. And boy, this has happened. I know that plant still exists; I might even be able to get some back some year.

So I’m just trying in a few things in the garden, and also with a couple of houseplants that have been admired, like philodendron that have very thick stems. I’m doing the same thing, and then the aerial roots. I know you’re running out of time, huh?

Margaret: Yep. Well, because the mad propagator, you have to get back to your babies anyway.

Ken: I know. You get me so excited.

Margaret: Well, no, I’m glad that I asked. I didn’t know about the air layering. It’s a subject for a whole other show. Thank you, and I’ll talk to you soon.

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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 May 29, 2023 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. Polly Farrington says:

    Great episode! My flats of primula are coming along very, very slowly. Like Ken’s, I started mine outside and have them in big flat containers, protected by a hardware cloth. Sitting in the shade, they’re trying to get bigger. Hope they make it! Didn’t get them started as early as I would have liked, the seeds from PlantWorkd were held up by the UK postal strike this past winter. Hope Ken will keep us up to date on how his primroses fare!

  2. Anne Sickinger says:

    I had forgotten all about primroses! Got to get some seed and try this. I’ve had very good luck with winter sowing. It’s perfect for a lazy gardener or someone who is just the opposite and has sooooo many things they want to do , that they want to eliminate as many steps as they can in these processes! Thank you for your information Margaret and Ken!

  3. Paul Otto says:

    The American Primrose Society has an excellent seed list in December every year. The seed is very affordable and germinates well. Also, no importation problems.

  4. I just wanted to mention that you didn’t list The American Primrose Society as a one of the best sources of Primula anywhere. Ken joined the society in the past year but didn’t order seed….I wondered why. I manage the seed exchange and we receive Primula seed from all over the world. You can order up to 20 packets as an APS member for a very small cost. Check out the past years list here…. https://americanprimrosesociety.org/seed-list/ The next exchange will open in mid-December. Give the society a try!

    1. Deborah Banks says:

      And then APS has the “Lucky Dip” seed madness in March! This is when non-members also can order seeds; there’s always lots of varieties still available.

  5. Paulette says:

    When planting tiny seeds in mass I mix seeds with regular table sugar. Lots of sugar and small amount of seeds. Then I broadcast them in the flat, ground or winter seeding container. The sugar lets me see where I ‘sprinkled’ AND it just naturally thins the seeding. Then when the seeds sprout the seedling plants are not ‘packed’ in soPauthick. This makes it much easier and MUCH more successful in moving the plants to there finial growing location.

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