Horticulture Week Podcast transcript - Soil Association's Ben Raskin on woodchip, agroforestry and going peat-free

Below is a transcript of the Horticulture Week podcast with the Soil Association's Ben Raskin.

Ben Raskin, head of horticulture and agroforestry at the Soil Association, explodes a few myths around woodchip, benefits and its commercial potential. He also discusses the use of peat in horticulture and reveals his 'desert island plant'.


Matthew Appleby (MA)
Ben Raskin (BA)

MA: Hello and welcome to the Horticulture Week Podcast. I'm Horticulture Week editor, Matthew Appleby and today I'm with Ben Raskin, head of horticulture and agroforestry at the Soil Association. Now, Ben has been working in horticulture for more than 25 years and has been with the Soil Association since 2006.

The co-chairs the DEFRA edibles horticulture round table, and his experience includes running a walled garden in Sussex, supplying a Michelin-starred restaurant - sounds interesting - and working for Garden Organic at their gardens in Kent. And he also set up and ran a 10-acre horticultural production, farm at Daylesford and moved to the Welsh college of horticulture as a commercial manager after that.

He's also worked in project managing agroforestry, but most recently, which is what we're talking about mostly today, he's got a new book out called the Woodchip Handbook and it's a really useful overview of the possibilities afforded by woodchip for growers and landscapers at any scale from the farm to the garden, to the greenhouse, and even on my allotment!

So hello, Ben, how are you?

BR: Hi Matthew. Yeah. All good. Thank you.

MA: Thanks for coming on. Now, a little while since I talked to you, so how have you been coping joined lockdown? What's been going on with you?

BR: Well, it's plusses and minuses, I guess like most people, I think. The offices or shut down in the association and we were all sent off to work from home, which is okay for me. I have a little tiny little garden office, which was okay.

I think I was saved by the work I do on the agroforestry at the farm. Once a week, I was over looking after trees and that definitely helped my mental sanity. I think, I think I've otherwise I'd have been a bit stir crazy.

MA:  I think the garden and getting into nature has helped a lot of people and I've been getting into nature in the last few weeks - winter on the allotment. I'm just talking to you about it before we started this, throwing a load of wood chip on it.

But with your book and woodchip, our audience would be interested about woodchip and commercial purposes: propagation, landscaping, mulching, soil health. So how does woodchip work for commercial purposes? How is it good commercially?

BR: So, I mean, you've outlined a few of them there. I think as a mulch, it's fairly well known to be a useful thing to do. I think one of the things I've found when I was researching the book was it was even more useful than I thought.

So in landscaping, obviously it, you know, it helps cuts weeds out. It helps hold moisture and so up to 25% increase in soil moisture, for instance. But there's other things happening as well on the mulch. Particularly if it's not composted mulch, if it's freshly chipped wood, there will be, allopathic chemicals in it that stop weed germination, so it can actually work chemically to prevent weeds as well as smothering them through blocking out light. So yeah, lots of interesting stuff going on. And then once it's on the soil, obviously as it breaks down it's releasing organic matter into the soil and building particularly soil fungi and we're really only now, I think, starting to understand the role soil fungi play, and sequestering carbon, but also the transport of nutrients around under the soil and just general health particularly for woody plants, trees and shrubs.

MA: And what about propagation? Can you you use woodchip for that?

BR: Well you can, and again, I think there's a few myths around woodchip. Some of them have some basis but they've potentially been a bit overblown, I think over the years.

And one of them is that you can't use wood chip and compost. And we did a trial, actually the Soil Association with the Innovative Farmers program that we do using composted woodchip as a propagation compost substrate. So it was basically just composted woodchip, a little tiny bit of the packhouse waste went into it as well, but it was mostly woodchip turned a few times over the summer, left for effectively 18 months to rot down and then sieved with a little bit of biochar added in.

We trialled it with leaks and cabbage. There's a grower and called Iain Tolhurst Berkshire who's an amazing grower. I'm sure some of your listeners will know of him. And it performed comparably to one of the leading peat-based propagation composts. Actually one of the leek crops had less disease with the woodchip composts when it was out in the field, so I think the success of that actually surprised quite a few of us.

MA: No, I know, I know [Iain Tolhurst] - one of my heroes: a vegan grower, a commercial vegan grower! But whenever I mention this, using woodchip on my allotment - and I talked to our technical editor, Sally Drury about it, and she said: 'oh, be careful of the nitrogen, you know, it might starve all your plants'. So is that a concern or is that a myth?

BR: Yeah, so, I mean, it's both in a way. So I think there is a genuine risk of nitrogen robbing, but actually it's a very low risk, and I think there's two things to be aware of: one is not to dig in particularly fresh woodchip, that's when the problems come. So it seems to be that it robs nitrogen from maybe around sort of one centimeter where it touches the soil. If you just put it down as a mulch on top, you're effectively only affecting that top, potentially one centimeter of soil. As soon as you dig it in, of course, there's lots of soil touching all of the chip and that's when the problems occur.

The other potential issue is very shallow rooted plants. Now I think I saw a problem on some of my raspberries, for instance, which obviously send out these sort of very shallow runners under the soil. So there is some risk, but mostly it's pretty low. If you're, if you're mulching trees, the roots are deep enough, I think for not to be affected, but if you're concerned, then you can just compost it for six/nine months first, and that will start the breakdown period, and then when you add it there's much less risk of the nitrogen robbing. But then if you're using it for vegetable beds or, you know, no dig beds or vegetable production, I would recommend composting it.

MA: Brilliant advice there Ben, thanks for that. Now what about sourcing and cost? How do you get hold of it? How much does it cost in comparison to other materials?

BR: So, yeah it does vary a lot and it varies partly on where you are in the country. So some places you seem to be able to get hold of it relatively easily.

I was talking to a grower in the Midlands who said they can't get hold of any now from tree surgeons. It's all being taken up. I think people are beginning to value it more and I'm sure after my book even more so (!) but I think, whereas for some, some tree surgeons particularly, it's still a waste product that they have to pay to get rid of. But I think some of them are starting to see there's a value in creating a product themselves. Others are now in a position where they might even be able to start charging a little bit to farmers and growers that want it.

But certainly where we are in Wiltshire, we're still getting free woodchip from two tree surgeons. There's a website Arbtalk.co.uk where you can register yourself as tip site.

I think if you've got the space to grow your own, then you get more control over it. So inevitably if you're taking stuff from tree surgeons, it's a mix of stuff. You can't really guarantee what species it is. There might be some diseased wood in there, which again, we can talk about. I don't think it's a massive problem, but it's a bit of a risk and I've even had, you know, the odd chainsaw helmet or sack or something in there that got in there by mistake, whereas if you're growing your own, you can potentially grow single species with a particular property, or you can make sure that it's all a particular size chip, which might go through a spreader more easily. So if you've got the space to grow your own, there's a cost to that, obviously, but it gives you more control over the product.

MA: Great. What about willow woodchip and preventing tree diseases. Can you tell us a bit about that?

BR: Yeah, so that was another Innovative Farmers field lab we did and there's researcher Glyn Percival, who works with trees, who noticed in, in another study he was doing that where he was mulching with single species woodchips and he noticed that the apple trees that had the willow woodchip on seem to have less scab. So we picked up on this with him and trialled with some cider orchards in Somerset some to see if we could replicate that practically out in the orchard. The concept basically is the salycilic acid in the willow, which is aspirin effectively, seems to stimulate an immune reaction in the tree to make it better able to fight, in this case, scab, but potentially a whole range of diseases.

The trial wasn't conclusive, but it did show a trend towards a reduction in scab. There's a few factors:

One is that different willows have quite different levels of salycilic acid in them. We weren't always using the variety with the highest level so that'd be one thing.

It's also much higher concentration in the bark of the willow so if we could find the source of willow bark, for instance, that would work.

There'salso some sort of critical bits around timing. You have to harvest and chip the willow when the sap starts to rise in February, but then you have to apply it pretty quickly because otherwise it all leaches out. So it does get a little bit complicated, but, but there definitely seems to be something in it. So yeah, really interesting.

MA: Glyn Percival from Bartlett's always full of innovative ideas . You mentioned woodchip becoming more of a commercial product possibly and being worth more money. Do you think it's going to be a sort of product which is going to be generally for sale  in garden centres for same price as say compost and people are going to buy it by the sackful?

BR: I think it might be, I mean, I'm already starting to see it. I was at a farm shop the other day and they were selling ton bags of, I can't remember, sort of three or four different products. One of them was woodchip and it seems to go for a ton bag for anywhere between £50 and £150. So I think there is a value in it.

I think for gardeners, where they might not be able to have a big load dumped by a tree surgeon but still want to get hold of some, there are people selling 80-100 litre bags, there are people selling ton bags.

I think there's a market and I think it will develop as people understand the role. The interesting thing for me is how it ties into the biomass woodchip market, which obviously sucks up a lot of woodchip. If we can get more towards, solar and wind and woodchip used in biomass is reduced that could release more for horticultural purposes.

MA: Indeed. You mentioned Thomas the vegan grower before, I guess this is a good alternative to using animal manures.

BR: It is. And I mean, it's not a fertility product in a sense. I wouldn't use it as a source of nutrient in that sense. It's about boosting soil health.

And Tommy, he's been using composted woodchip on his soils for about 10 years and he says that he's seen a step change in productivity since he started putting woodchip on. One of the things actually prompted me to look at writing the book was standing in a field with him, looking at his soil where he'd put the woodchip a couple of months earlier and there wasn't a bit of his soil that wasn't a worm cast. The biological activity in the soil was incredible. And he's not on the best land he's on grade 3 soil. It's not where you would choose to grow vegetables but crops are astonishing and the soil is so alive and he definitely puts up quite a bit of that down to to the woodchip.

MA: It's really interesting, innovative stuff. Now you mentioned peat earlier on. Now peat is a big issue at the moment. We did a survey recently of our readership basically [asking] do you want to keep peat or not? We didn't know what the answer was going to be and 76% said they want to keep it, which is basically the silent majority, as far as I can see.

BR: I was one of the minority, I'd have to confirm!

MA: Well, no, I mean we honestly didn't know what the answer was going to be, but I just thought it a question well worth asking because peat is getting to a critical point where, if people want to keep it, they're going to have to do something about it now because the Government is due to act.

So what's your view on where peat's going?

BR: I my personal view is in the long term there isn't a reason to be using it. You know, we grew lots of stuff before we discovered we could use peat and that clearly the industry at the moment is not in a position to be able to turn around next year and say, right, let's do without peat - there's no question. Particularly, there are things like mushrooms where we're probably quite a long way off. But my view is there are alternatives. We're an inventive species; we can find alternatives. And the fact that with the propagation compost trial, we did, you know, someone on a farm can just pile up woodchip and rot it down and propagate vegetables, I don't see that technically it's impossible to find a way to replace peat.

I think we do need more pressure. I think we've been prevaricating probably for too long, but equally, I also understand we can't just turn around and pull the rug out from systems that have developed to rely on it.

But there is a cost issue. You know, peat is used because it's a good product and it's easy to use and it's cheap and it's plentiful, you just dig it out of the ground. People are going to have to accept the fact that some of these things, if we care about the environment, the cost of food will have to go up because we can't just always find the cheapest solution when there are other impacts. That's my view!

MA: Well worth listening to, and do you think there need to be exceptions? I mean, you mentioned mushrooms. Do you think there should be exceptions,  for a number of years?

BR: Well, yeah, I would see them as temporary exceptions, certainly. I think we need a more detailed roadmap.

I think even at the moment where people are starting to move away from peat there's problems with supply of alternative materials. It's obviously going to take time to build up a supply chain of those alternatives and I think the mushroom industry probably has been slower than the horticultural industry to start developing some of these.

But I think increasingly consumers are asking questions about how their food is produced. The Soil Association, we now get much more informed questions from our supporters or, you know, people interested than we did 10 years ago. 10 years ago it might just have been enough that it was organic. Now they [say] 'well, hang on, I've read that, you know, you still allow peat and organic -that's terrible'. You know, they really care about this stuff, and I think we have to keep moving forward. But it's clearly not easy with some crops.

MA: No, no, I see. Well, there's a lot going on in both environmentally and politically at the moment. we just had COP26 quite recently, we're working through the pandemic and Brexit. The Soil Association has a big role to play in this. Do you think the Soil Association and horticulture has, kind of, come of age as a political voice at the moment?

BR: Well, I hope so. I think the whole conversation around environmental organic, sustainable farming - however you want to frame it - I think has changed unbelievably in the last five years.

Certainly over the 15 years I've been at the Soil Association, two things have happened: one is I think the organic sector has become more outward-looking and willing to engage and I think the rest of the world has become more aware of the challenges that are facing our food production system and the planet.

Whereas 10 years ago I well remember people crossing the room to avoid me at a conference (!), if they knew us from the Soil Association, now the opposite is true and we can't keep up at the moment, in the Soil Association, with the opportunities to do work. We're engaged in so many funding beds it is a bit scary. But it's really positive and it's really encouraging. I think, for us, whether people choose to be organically certified or not, I think almost everybody's now is looking at producing more environmentally.

MA: But now you're involved in the DEFRA edibles horticulture at round table. What are they up to at the moment?

BR: So that comes out of the Fruit and Veg Alliance, which is a big group of,  fruit and vegetable producers and some other organizations and we work closely with the horticultural team in DEFRA.

As your listeners will know, it's a difficult time at the moment. There's real challenges from both Covid and Brexit. Um, as well as all those wider, longer term things we talked about. We really try and work very constructively with the DEFRA horticultural team who are very much on our side but we're not always able to achieve what they want to in wider government because there are other departments like the Home Office and things that sometimes have a more powerful voice.

But I would urge anyone to support the Fruit and Veg Alliance and the work of the round table and if they have things that they want to bring to the attention of the horticultural team in DEFRA, then it's a good way in, it's a good voice. There's lots of organizations that I suspect most of your listeners will be aware of that can they can feed through.

MA: Now another area which has had a bit of a voice in parliament in recent times is agroforestry. Carrie McCarthy's talked a bit about this at various meetings and you're involved in agroforestry too. So what what's agroforestry is role for the future do you think?

I see agroforestry as potentially one of the biggest ways we can change the the way that we farm.

As I'm sure most of your listeners know, it's the integration of trees into farming or growing, so rather than separate them out, you grow them together. In livestock farming I think there's almost no downsides. In most situations you can increase productivity and environmental goods, animal welfare, all of that sort of thing quite quickly.

I think in crop situations, it becomes a little trickier. I think the benefits are still there and the potential productivity gains are still there but it gets a little bit more complicated because you will lose some of the yield of the crop. That should be outweighed by the extra yield that you bring in through the tree production, but it requires a bit more balancing and often a slightly longer term investment which makes it, I think, a little bit trickier for cropping and, you know, arable and horticulture than it would for livestock.

I'm really interested in the potential for nut crops. For instance, we there's a massive market for nut crops. We import almost all of them at the moment. We grow very little in this country. We don't have that much processing capacity at the moment. We don't have marketing channels but lots of farmers are starting to plant up areas of, for instance, walnuts and chestnuts. I'm growing some almonds in Wiltshire, which is a little speculative, but that growing well, not producing very much yet but they're growing well. You can then start to produce more protein crops in the UK, for instance, and, and if you can design the system right, then it shouldn't impact on the amount of crops we can bring. So, yeah, I think there's huge potential, but it's not always easy and it's quite expensive and it needs a long-term view and some support, which hopefully the Government are going to be announcing soon, we hope.

MA: Oh, brilliant. Now we've certainly covered some interesting new ground there, but talking of nuts, we're going to go back to an old chestnut question, Ben, just to finish. What is your 'desert island plant? What plant would you take if you were stranded on a desert?

Well, I am going to choose a nut tree. I'm going to choose a walnut tree because I love walnuts and I can sit under the shade on the desert island and I can catch the nuts as they fall into my hand. And I don't need a nutcracker. I can just find a stone and gently crack open the walnuts.

MA: Sounds idyllic. Well, thanks for listening to the Horticulture Week Podcast. I'm Matthew Appleby and I've been with Ben Raskin.

Now make sure you never miss a Horticulture Week podcast. Subscribe to or follow Horticulture Week Podcast via Apple podcasts, Spotify, Google podcasts, or your preferred podcast platform. If you're interested in producing a podcast before week contact matthew.appleby@haymarket.com.

Once again. Thanks and goodbye until the next time.

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