GARDENERS HAVE increasingly heard the call to reduce or eliminate their use of peat moss, the most familiar ingredient in seed-starting mixes and potting soils—one that a lot of us have long relied on. But peat is not sustainable, and its harvest releases substantial CO2, a greenhouse gas that contributes to climate change. So what to use instead?

That’s our topic with North Carolina State University Professor Brian Jackson, an expert in soilless growing media or soilless substrates, as they are also called.

Brian Jackson is a professor in the Department of Horticultural Science at North Carolina State, and director of the university’s Horticultural Substrate Laboratory. He’s one of perhaps five U.S. scientists at public universities studying these materials and their role in horticulture and agriculture. (Below, Dr. Jackson alongside a pile of engineered wood fiber being processed by heating to stabilize and sterilize them, for use as a substrate. He predicts such materials will fill the largest part of the peat-alternative puzzle globally.)

Read along as you listen to the March 7, 2022 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).

reducing peat moss use, with brian jackson

Margaret Roach: I learned so much, Brian, working together on a recent “New York Times” garden column about this subject, and I look forward to learning more today and sharing it with everybody. I know that listeners are going to be eager for your advice, excuse me, on kind of like what to use, the season, and what to set their seedlings in, and all kinds of good things like that.

But before we get there, I think maybe we should set the scene, because there’s current environmental and also economic… sort of a backdrop of both here. And it’s kind of different in the U.K. and Europe. And peat’s in high demand. But, oh my goodness. So maybe you could kind of set the scene. So, a lot going on [laughter]. Uh-oh, did I make a big task for you there?

Brian Jackson: [Laughter.] Oh my goodness. It is. And, thank you again for the opportunity. Yeah. What an exciting, yet challenging, time to be in horticultural production research, and to work in an area that involves both consumers of garden products, as well as professional growers, who rely so heavily on these unique materials to grow our food crops and our flowers and ornamental crops.

So I guess a brief overview, just to get us on the same page: Peat moss as an organic material used in pot soils to grow crops has been predominant since the 1960s and for the last 50, 60 years has been, as I quoted you Margaret, “The Rolls-Royce of growing media.”

Margaret: Yes.

Brian: And it is. And, so one of the first things I would mention is peat moss can never be replaced, because we cannot replace anything. Same with us. We can offer alternatives. And I think that’s where this conversation is going, and other publications about alternatives. Peat moss across Europe has been used for centuries as a fuel source, and that’s one of the reasons why some of the peatlands in Europe have not been managed as properly as they should have been before we knew better, quite frankly.

Margaret: Right. I mean, I remember in the story quoting that only 22 percent of the peatlands in the United Kingdom, for instance, are in a, “near natural or rewetted condition.” Almost 80 percent of them are in some way impacted already.

Brian: Correct. And one of the other things I think is important to think about in regards to looking at peat and its sustainability or its impact on environmental concerns, only 0.05 percent of peat globally has been extracted for horticultural purposes.

Margaret: Right.

Brian: The other extraction has been for agriculture, fuel and forestry that’s kind of taken these resources. So therein lies the crux of the problem in Europe, is they haven’t done it properly from the beginning, so now they’re having to really assess peat’s use moving forward, and how other materials can help supplement and extend those peat supplies.

And then in Canada, of course, who supplies the vast majority of our materials in North America, the Canadian industry is younger. It’s only 50, 60 years old, give or take, and they’re doing things much better from an environmental perspective.

Margaret: And we weren’t harvesting, extracting it, to heat our houses.

Brian: Exactly.

Margaret: That was never the purpose.

Brian: Exactly.

Margaret: Right.

Brian: That’s correct.

Margaret: Right. O.K. So, and I remember—again, statistics-wise—that Canada, I think, has an estimated 27 percent of the world’s peatlands in terms of acreage, but 0.03 percent of them are currently harvested or have been harvested. [Above, a Canadian bog with a drainage ditch to help dry the area. Peat is harvested by vacuuming from the surface in summer.]

Brian: Correct. That is correct.

Margaret: So again—and I’m not and I don’t think you are, we’re not trying to greenwash this or anything and say, “Oh, hey, no….” In fact, every time you extract peat, it does release a substantial amount of CO2. And there’s no getting around that.

Brian: It does.

Margaret: Yeah. It’s just that we’re trying to say perspective-wise, hopefully, hopefully, the Canadian industry has been doing an O.K. job so far. And we’ll see. And they’re not going to stop harvesting, are they? I mean…

Brian: They’re not Margaret, and that’s a great point.

Margaret: Yeah.

Brian: There’s a lot of initiatives that they are taking to minimize or to mitigate their environmental impact and carbon emissions, but there is some that happens. So, they’re working hard to try to do the best they can. And that’s true for any other material that we use has some impact, and we’re all trying to mitigate that to the best of our abilities.

Margaret: Right. Now in the U.K., though, there are bans that are coming up, for instance, horticultural products, for garden products, and eventually for commercial products. There’s timelines for stopping the use of peat in those products and so forth. And they’re already on that timeline, I think.

Brian: Yes. Yes. Ireland was the first to ban peat extraction, in 2020.

Margaret: Right.

Brian: The United Kingdom, including all four of its nations, is set to limit or to actually stop peat use in the hobby market in 2024, and then the professional market by 2030. And there are seven or eight other countries in Europe that have level of conversation or regulation in mind about how to address this moving forward.

It’s certainly a critical issue certainly as growing media and different growing media types are so important in how we grow food and other crops for the future.

Margaret: Right. So, it’s a time of very high demand, and a time I’m of environmental awareness converging to make a very complicated kind of moment.

Brian: It is a perfect storm. You’re correct.

Margaret: Yeah. Yeah. So you are in the business, or the research business, of researching soilless growing media or soilless substrates [laughter]. Tell us what a substrate is, because you add all the lingo, you scientist types. And what are the other materials besides peat in that sort of palette of soilless substrates?

Brian: Yeah. That’s a great question. And a substrate is just basically a material on which something grows. And some people, if you’re taking microbiology, you use a substrate in a little Petri dish to grow cell culture or something. So substrate, we always use the word soilless or horticultural in front of that, but it is potting soil, potting medium, growing mix.

So other than peat, thinking organic materials, carbon-based materials, of course you’ve got the coconut products coming out of the Philippines in Sri Lanka and South India and Mexico. Coconut coir, as it’s called. Compost. You’ve got bark, aged and composted barks. You’ve got rice hulls. There are a lot of different organic materials that are being used in soilless media.

And then you’ve got the inorganics, those that are not carbon-based like perlite, or vermiculite, or rock or stone wool, or clay pebbles. So, there’s a really a quite decent size palette of these different ingredients that for 50 years we’ve formulated some really unique mixes.

Margaret: Now, before the 1960s, or whatever, before peat became the Rolls-Royce [laughter], was the commercial, where pot potted plants and so forth, was it soil, actual soil, that was used as the medium? I mean, was that what things were potted up in, or was it just because it was before the giant mechanization of the greenhouse industry and the mass production of plants and so forth?

Brian: Yeah. Great question. Yeah, it truly was when people started growing crops, plants, in containers. And in the early days of containers, there were actually egg cans and other commercial food-grade cans that were used to grow plants. Metal cans [laughter]. And the only… Yeah, it’s really fascinating, the history of the container or the containerized system that we now have the options. It’s really fascinating. And most of the time they used mineral soil, field soil, to fill in these pots. And they quickly realized that based on the weight… Think about a one-gallon pot of sand or soil.

That is so heavy. And then the water, it’s like a bathtub, it holds so much water it just doesn’t drain properly. So yeah, it was soil that was used predominantly before a sand-peat mix, and then more and more away from the sand, and then discovery of these other lightweight, sterile or beneficial organic materials.

Margaret: So if we start to get practical, the sort of how-to stuff, you are at North Carolina State, a tremendously important university for horticulture and agricultural research and so forth, and training the future experts in these fields

Do you have greenhouses full of mad-scientist experiments with trying all kinds of media, and comparing these tomatoes to those tomatoes and these petunias to those petunias? But, I mean, is that kind of what’s going on and trying to figure out, “Hey, what else can we use”? Is it that way? Is that where the research is done?

Brian: Yeah. Have you looked inside of my greenhouse? I think you have.

Margaret: Apparently, I’ve seen the mad scientist at work [laughter].

Brian: You have. So, the great thing about research is you can get creative and really think outside of that proverbial box we always talk about and really think about what are some new options? What are some things to do?

So we test so many different materials through a battery of different procedures and analysis techniques to assess their potential in growing plants in different systems. And making sure that what we are doing to formulate new materials and new mixes is not only adequate for plant growth, but it’s also economical and it also is recyclable or can be reused.

So, there’s a long list of 50 years of research that’s kind of gotten us to a point of how do we evaluate new materials from start to finish? And it’s really not… We don’t really throw the kitchen sink at this, in regards to how to approach the science behind development of new products.

It’s a really detailed list of parameters that’s been developed over the years that give us a higher level of success when we’re looking at a new material. For example, hemp fiber or Miscanthus or other biomass crops that may have potential as soilless growing-media components. [Above, Gerbera daisies grown in a peat-free mix (left) and in peat-perlite.]

Margaret: I’ve even seen on the market these days products that are labeled as substitutes for potting soil or for seed-starting mix that are made of paper, recycled newsprint type of paper, and all kinds of things.

Brian: Absolutely.

Margaret: I mean, there are lots of ideas out there.

Brian: There are. And thanks to the article recently in the Times, Margaret, I’ve been contacted by a lot of folks. And what I have learned, and one of the great things about this contribution, or this collaboration, I have learned of companies and products on the market in the United States that I have never heard of. And it’s not to say that they aren’t relevant, it’s just there’s a lot out there in this big country of ours.

So I now know of companies and products that are peat alternatives, that are completely peat free and have been for a number of years and are being very successful. So, I’ve been encouraged by the development that’s went on. And I didn’t know about it, which again, that’s not to say that I knew everything by no stretch of the imagination, but we’re further along than I thought.

Margaret: Right.

Brian: So I think this article has helped open that perspective up,

Margaret: Right. Because I looked, of course, longingly over at the UK where, again, the bans are impending or in place for horticultural products. And I saw that the Royal Horticultural Society already had branded a whole line of potting soils and so forth with a particular company. And I was like, “Oh wait, can we have those?” [Laughter.]

But no, we didn’t yet. And so what we do have is we have some smaller, innovative companies and some medium-size, innovative companies, and people trying things. But here’s the thing, and this is what I want to spend some time asking you about because you, again, have the experience hands-on in the greenhouses and so forth doing the research. And you’re actually also trying to not make sure I can grow my seedlings, little Margaret with her couple of trays.

You’re talking about the entire industry. And as you pointed out, that’s an industry that it provides the potting media for our food, many of our food crops.

Brian: Absolutely.

Margaret: And it’s not just like, “Oh, Margaret’s going to have a couple of little petunias over there.” It’s a big deal. It’s massive, the basis of our agricultural and horticultural production systems.

So, I’m hearing from a lot of people who—and expert gardeners, friends I’ve known for a long time who are serious, good propagators, they grow lots of different things. And they’re saying, “Well, I tried such and such and everything died.” Or, “I tried this and my seedlings were stunted.” And then another person calls me and says the same product and they did great with it [laughter], so it’s like, “Oh my goodness.” You know what I mean?

It’s not like it’s the roadmap is all figured out. We got to do some experimenting. And I just wonder, where do we start?

Because in the Times article we talked about how maybe we sort of warn people, “Maybe your seedlings, the most vulnerable babies, maybe you don’t want to throw everything at them right away. Maybe you want to go slowly with those.” So tell me, where would you begin and helping a gardener like myself, like the listeners, in making this transition, if they wish to for environmental reasons to be environmentally conscious?

Brian: Yeah. Great point. I would say, and this is a really neat point that you brought up, for how we develop professional mixes to provide the really large greenhouses and controlled environment, vertical farms, nurseries, for those materials have to go through different criteria and there are different expectations of them than consumer hobby market products.

Margaret: Yes.

Brian: So even from the article, you hear people say, “Well, I’ve used this and it works great.” But think about a 100-acre greenhouse. Or think about 5,000 acres of greenhouses that need 500,000 cubic yards of the same material. That’s where things get really challenging on that scale.

Margaret: Yes.

Brian: So, it’s a really neat point thinking of the consumer home gardener who wants to make that choice. Even I wish I could go back and us do the article again [laughter], because I could shed light on other product development that there are peat alternative options that even for seed starters apparently are really quite good.

So, I would advise to do one’s homework is always a good thing to do before trying something. And maybe there are products you could either order online and have delivered to you, but then thinking of sustainability, how does that factor in as well?

Margaret: Yeah.

Brian: Or what does your local garden center have and what is the opinion of the experts at that garden center as to what products they can either order in or could perhaps request that are peat free? Because there are options out there.

So start slow. Do one’s homework. Do not expect that, as we mentioned in the article, that any new material or new approach to doing something is going to be the same as what you’ve all always done, because there may be nuances. So, yeah, I think those are the places that anyone can start. And then asking yourself, is this product that I’m using is it worth the price, or is it truly better than peat? And that’s a conversation that we can continue to have, and that will continue to evolve as we move forward.

Margaret: Yeah. So it’s like say I’m going to start… And again, I have a number of friends who are all in this sort of experimenting stage, and have expertise and are successful seed-sowers or successful with whatever they’re growing in pots and so forth and trays.

And what they’re doing is, and what I’m going to do this year, as we’ve talked about before, you and I, I’m not going to just stop using… I always used Johnny’s Selected Seeds, the Johnny’s 512 mix. That was my thing. I know how it feels. I know how it works. I know how it handles water. Do you know what I mean? It’s like, I have the feel of it. And I made that analogy, thay it’s like the first time I tried a gluten-free flour, the cake was a disaster [laughter].

Do you know what I mean? Because I didn’t know what I was doing and it wasn’t a one-to-one substitute and blah, blah, blah. And it wasn’t as moist. And, oh my goodness. So, that was my thing, but I want something that has that type of result.

So what a lot of my friends are doing, and what I’m thinking of doing, is kind of not if I have six flats going, filling them all with some unknown material that I’ve never handled or worked with before, but maybe doing one experimental flat with a couple of six-packs of something in it. But not losing all my crops, in case I don’t have a good experience.

Does that make sense to you? Are you doing it gingerly, too, when you’re experimenting? [Above, some fiber pots of seedlings at Margaret’s.]

Brian: It does. And I think one of the other things that I would highly suggest is to read the label on any new product because, Margaret, if your traditional go-to brand that you’ve always used, which maybe is a peat-perlite mix, for example. If it has some type of starter-charge nutrient in it that perhaps a peat-alternative product doesn’t have, then you need to make sure to know that just so that you’re not expecting the same thing. Not only as you mentioned from the watering front, but that also that you’re not under- or over-fertilizing those very sensitive young plants.

Margaret: Yes.

Brian: So also look at the nutrient charges and them. And yeah, just buy a small bag and just compare it to the others before going big scale, and understand that there may be differences. Maybe you like it better or worse, but also be willing to adjust your practices.

Margaret: Yeah. I’m thinking of adding, trying to extend my… I have a part of a leftover bag of my 512 mix, and I’m thinking of maybe I’m going to add some coir to it or… Do you know what I mean? I’m thinking of gradually feeling my way through, it in a sense.

Brian: Yeah. And what we may find thanks to technology and thanks to advancements in product development from big and large companies that even I don’t know about, as referenced earlier, there may be some products that there are no learning curves. And that’s even better. And I think through sharing and through platforms by which we educate each other that we begin to help everyone understand kind of what the current options are. [Below, more experiments in the NCSU research greenhouses.]

Margaret: Right. And what I’m hearing from friends, the ones who are working in greenhouses like at public gardens and stuff like that, are having a different experience with their experiments than the ones who are just a home person with a couple trays. And there’s different environments, different humidity, different temperatures, different air circulation. I mean, a lot of different factors that are going on that can, I think, impact success with any growing medium.

Brian: Oh, yes. Yeah. It’s a great point. It’s like for the companies that I work with on retail hobby-market products, also think are you growing in Upstate New York or are you growing in the south of Florida?

And that makes an individual product used in two different locations, perhaps very different as to how it behaves. So also, yeah, think about your location as well in regards to temperature, and sunlight, and humidity, and cloudy days or sunny days, and all of those things factor in as well.

Margaret: Right. And one of your greatest areas, greatest depth of expertise or what you’ve been exploring, are wood products. And I always, for potting bigger plants and so forth, I always used a bark-based mix. Doesn’t mean it didn’t have peat in it, but the primary ingredient was bark-based.

And it was a little more textural. You’re working with and researching and trying to figure out how we can use a renewable resource, wood, in various forms, not just bark, in soilless mixes, right? Is that the direction that’s going to make up some of this great demand, and allow people to maybe reduce their peat use, too? Is that where it’s going to go?

Brian: Yeah. It truly is, Margaret. Globally speaking, engineered wood fibers viewed as the most probable and likely raw material that is immediately ready, or will be ready, to fill that void of an increased demand as the peat supplies may or may not be limited moving forward. And I know a lot of your listeners may be thinking, “Well, you can’t grow plants in wood. Wood robs nitrogen. Wood is bad.”

Margaret: [Laughter.]

Brian: But propagators, primarily in California, have been using sawdust and propagation of woody plants since the 1940s and ’50s. But only until the 1980s did products of truly used wood fiber, not bark, but the actual white wood itself. And products have been on the market for a long time, but really didn’t gain interest until about seven or eight years ago, for all the reasons that we’ve discussed.

So, I started looking at engineered wood fibers in 2005, as part of my PhD work. And I still… It’s my life blood as to what I am focused on. And there’s a lot of potential for engineered wood fiber, even in consumer products that likely are already in some products that users may not know about. But there’s a lot we need to learn. But there’s a lot of potential in true non-composted wood fibers.

Margaret: It’s very exciting. I mean, I actually think this environmental awareness and all the… It’s going to lead us to really positive developments in a lot of ways. And it’s exciting. And I’m so glad to learn from you and to talk to you, Brian Jackson from North Carolina State University. And just, I always like to go to the scientists as opposed to the marketers of commercial products [laughter] when I’m asking the question, and that’s why we started where we did. And you’re right, maybe we have to do a follow-up piece before long about some of the products that are out there, and what we’ve both learned. So, I really appreciate your making the time to talk with me.

Brian: Margaret, thank you so much my friend. It is a pleasure.

(Photos except as noted from Dr. Brian Jackson; 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 11th year in March 2020. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the March 7, 2022 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify