Orchard People

[00:00:00] Introduction and Disclaimer
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[00:00:33] Welcome to the Urban Forestry Radio Show
Welcome to the Urban Forestry Radio Show here on Reality Radio 101. In this radio show and podcast, we learn about fruit trees, permaculture, aboriculture, and so much more. So if you love trees and especially fruit trees, or if you're interested in living a more sustainable life, then this is the place for you.
I'm your host, Susan Poizner of the fruit tree care training website, orchardpeople. com. Thanks for tuning in. And enjoy the show. Welcome
to the urban forestry radio show with your host, Susan Poizner. To contact Susan live right now, send her an email. Instudio101@gmail.com
and now your host, Susan Poizner.
[00:01:38] Susan's Journey with Fruit Trees
Hi, everybody. Years ago, when I planted my first fruit trees, I had very little knowledge about the special needs that these trees have. But one thing I did realize at the time is that fruit trees, and in fact all trees, Benefit from mulching. Now over the years I have learned so much about proper fruit tree care, about the importance of correct annual pruning, training, fertility management, and so much more.
And I teach you about those things in my book, Growing Urban Orchards, and in my online fruit tree care course at OrchardPeople. com.
[00:02:20] The Importance of Mulching
But mulch. The amazing thing about mulch is that we're learning more and more about it all the time. Now, mulch is way more than just woodchips. Scientists today are testing different types of mulches to see how fruit trees respond.
For example, they're using woodchips or shredded paper, alfalfa, Even fruit tree prunings and some are even trying living mulches to see which ones work best. Now fruit tree mulching can be cheap and it can have incredible benefits, whether you're growing one tree or thousands. So that's what we're going to chat about in the show today.
And I have a fantastic guest who knows all about it.
[00:03:08] Introducing Professor David Granatstein
Professor David Granatstein is with the Washington State University Center for Society. And he's worked on sustainable agriculture and organic farming for over 35 years. He's done a number of really interesting studies on orchard mulching and crop covers.
And what he's learned is eye opening for any person who is growing a fruit tree. So now as we go along, you are probably going to have questions or comments that you want to share, and I really encourage you to do During the live show, send your emails to instudio101 at gmail. com. That's instudio101 at gmail.
com. Okay, so let's dig into today's show. On the line, I have Professor David Granatstein. David, thank you so much for coming on the show today. Very welcome, Susan. It's so nice to have you here. And when we spoke last, you and I had a nice chat on the phone.
[00:04:14] Early Studies on Fruit Tree Mulching
You were telling me about a study that you did back in the 90s.
about fruit tree mulches. How did that come about? Can you tell me a little bit about it? I sure can. We, grow our fruit trees here in Washington, but the bulk of our commercial production is in the central part of the state, which actually is very dry. It's almost a desert, you could say. And there, there's been a lot of interest in, do we need to modify the environment?
Because it's not a natural place for, any trees to grow. Actually, where a lot of our orchards are, there are no native trees. This is sagebrush country, These trees have been put in a very different environment than what they're used to. And we were wondering if there were things we could do to amend the soil itself or affect the soil surface that might lead to some beneficial results.
At the same time, there was interest, And looking at alternatives to herbicides, which are the typical treatment that's used in the tree row to keep the grass and whatnot away from the trunks. And a group up in British Columbia with Agriculture Canada was doing some testing of alternatives and mulching was part of their testing.
And we got connected and began cooperating from there.
[00:05:30] Types of Mulch Tested
So tell me a little bit about the testing that you were doing. What were the different types of mulch that you were testing? We, started from scratch. I had done some work with compost and I'd used compost both as an amendment in the soil as well as just applied to the surface, but in many ways, compost is not always a particularly suitable mulch.
It has too high of a nutrient load in many cases. So we started looking at other things that were lower nutrient content, typically things like woodchips, like straw, like shredded paper, which was a waste product that could be found in the area. We did test, what do I want to say, spoiled alfalfa hay.
That was another material that's around and we thought, maybe it is a nutrient source and it could be dual purpose that way. And then we tested some living mulches like white clover. We tested a winter rye that was planted in the fall and we tested a particular kind of mustard that was planted in the fall.
Okay, so let's go through and tell me, how did they do? How did they compare?
[00:06:37] Results of Mulch Testing
overall, I would say that the woodchips did very, well. We got about three years of weed control out of that particular application. And it was, say, four to six inch deep, so a lot of material. And that's one of the challenges.
But it did perform well in terms of suppressing weeds. We had definitely moisture conservation, water conservation, where we had that mulch compared to bare ground. We improved tree growth, and we didn't have any vole problems in that particular mulch, which was important. We knew the voles were an issue to watch, and indeed, they're a pretty important factor in how you can use mulches.
The shredded paper did a nice job of controlling weeds. Nothing seemed to like to grow in it or through it very much. But it did knit together to some extent and didn't blow with the wind. However, the sprayers that are used in the orchards did pick it up and it didn't work particularly well from that standpoint.
The alfalfa hay was not good, any weed seeds that might have blown in on it. They sprouted and had a wonderful potting mix to grow on. And it was too much nitrogen. We did have some issues with fruit maturity and fruit quality from that. But again, that was because to get a thick layer, we just put on way, way too much nitrogen, which we knew we were doing.
The white clover was very intriguing. For the first year and a half, it was exceptionally good. We had almost no weeds at all. The moisture use was not very different than bare ground, which surprised us. We had higher nitrogen in the trees from that, which it wasn't so much that it was a big problem. So we were getting our fertility from it, and we had better tree growth and fruit yield from it.
But we did get a bit of fruit quality problem in the fall because you couldn't turn the nitrogen off.
[00:08:27] Challenges with Nitrogen and Mulching
When you might want to pre harvest with it growing in the tree row, so let's backtrack a little bit now You talk about too much nitrogen, and I know that most of us who are growing fruit trees know That our fruit trees need nitrogen in order to grow in fact if you find your fruit tree doesn't have enough new growth You realize oh my goodness I have to make sure this tree has nitrogen, but when you and I were chatting on the phone We were talking about The control issue that with certain mulches you lose control over when, that nitrogen is going to the tree.
I like to compare it to, giving a kid, a little kid, chocolates and candy before bedtime. So it's time for them to go to sleep and you open up the big tin of, chocolate, candies, and cookies. And then they're bouncing all over the place. So let's talk a little bit more about nitrogen.
And how these mulches contribute nitrogen and why you even want to control that nutrient for your fruit trees. Fruit trees typically have a cycle of when nitrogen is needed and when it's actually a negative from the standpoint of, that we're trying to harvest. So an even supply year round, if it's an extremely low level, you might be able to get away with, but you also might have some deficiencies during certain times of the year.
If you put on a very thick layer of a mulch or something like the compost that I had mentioned, and it will start releasing. nitrogen as things warm up, and it will continue releasing it as long as there's adequate temperature and moisture. And in our environment, that would be, actually, you could have nitrogen coming out of a mulch or compost in December under the snow, so it can go clear on through into winter once it gets going.
So typically, we see high nitrogen demand in the spring, there's a big demand period in the spring and early summer, then the demand falls off as the fruit. is sizing and maturing. You don't want high nitrogen levels in the soil. And then once harvest is done, you want to rebuild the reserves for the next year.
And you have another need in the fall, but not too late because once the roots start to go dormant, the trees won't take it up. So finding that timing and it varies with species. It varies with the variety and whatnot. It is important if you put on so much organic material as a mulch. That you lose control that it's generating just large, amounts all season.
You're going to have that problem. If you grow a legume in the tree low tree row, like we tried with the clover. Similarly, it's going to be releasing nitrogen. Especially if you cut it at all, you'll get a pulse of nitrogen. So that's why putting a legume in the tree row was pretty obvious that was going to be a problem.
If you put it in the alley, however, which we've done some testing on, then you can grow, for example, a clover or an alfalfa in the alley. You can mow it and blow it onto the tree row during those times of the season when you want nitrogen. And when you don't, you mow it and leave it in place. And it gives you a bit.
Quite a bit more control. We'll talk about that a little later on in the show. But, so let's backtrack a bit and I've got a really interesting question here from Cheryl. Cheryl is, writing from Washington DC and she was reading my mind, I think because I wanted to ask you this.
[00:11:54] Living Mulches and Their Impact
She says, what is a living mulch?
Would a cover crop constitute a living mulch? She says, I'm growing some apple trees in containers. Okay, so you mentioned living mulches, you talked about clover, so tell us, define that for us, and how is Cheryl going to do with, clover in her pots with her fruit trees? Alas, I'm having a hard time imagining what it looks like in the pot, but a living mulch is essentially a cover crop.
It's something rather than, in our normal management, we give the trees a competition free space in that tree row. This is the standard management system in orchards today. It used to be that there was no vegetation in an orchard, but of course there's all sorts of problems that happen with that.
So now we have Sort of a zone system where we've got our alleys between the rows of the trees where the trunks are that are vegetated with permanent vegetation. It's a cover crop. It's typically grass, and that's to hold the soil in place, to give a good surface if you're driving equipment on it, to keep the dust down, to stop erosion, all those things.
And then in the tree row, typically, we want a competition free area, particularly for young trees. It's really critical to give those trees a chance, but in the longer term, you also have issues around moisture and some places they don't want any other vegetation using moisture because they're limited in their water.
So you'll see that system to keep a lot of the area vegetation free, but in many places where that's not such an issue, voles because vegetation. Near and next to the trunks creates habitat and possibly food for voles, and then they're attracted to it and may damage the trunks, particularly in the wintertime.
So a mulch is anything we're putting over the soil. Typically, we have what you could call inert mules, like woodchips or the black weed fabrics. A living mulch is simply filling that niche with a cover crop. to perform some function that we want it to do. So I want to clarify here for Cheryl and for lots of people.
I think I've been seeing a lot of examples where people are planting their living mulches and everybody says clover is wonderful and we all love clover, but they plant it Up to the tree, up and around and into the roots. And, David, when you're talking about competition, your young fruit tree really, for a person who's growing in their backyard, it needs nutrition.
It doesn't compete very well with other plants. if you, I've seen people plant strawberries right around and up to their fruit trees. Not only does that, pose a challenge when you're actually going to prune that tree, cause you have to step on your strawberries. But there's competition that's happening, so I guess, one of the things that you were saying is, it's thinking very carefully, these living mulches, or these cover crops, how close are you planting them to the tree?
would you agree to that? That you really, you've got to keep a little bit of distance? David? That's certainly what we've found, and many others have found, is that when you've got the young trees, they do need this competition, free space. And there's been a number of studies trying to determine just how much space is that.
It partly depends on the figure of the tree, if it's a dwarfing or semi dwarfing versus a full size tree. But nonetheless, it's probably going to be something like, foot and a half to two feet, maybe three, One 1. 5 meter wide strip overall is going to be vegetation free as you're getting that tree established for the first four or five, six years, depends on the strength of the soil as well as how much nutrient supplying power is there.
But that's where we've tried experiments with a quote living mulch in a mature orchard versus in a newly planted orchard and the results were dramatically different. So absolutely. using a living mulch on a new planting, I would not recommend that. I think the competition factor is very significant.
That's so interesting. And yet, when you're working with trees that have been in the ground for 10 years or 20 years, if the living mulch like that clover planted in the ground starts creeping up towards the root system of the tree, it's not as much of a problem, because that tree has way more roots doing a lot more work, consuming more water.
Is that the thing? Correct. It's already got an established root system. The nature of the particular living mulch will matter. The nature of the tree will matter. How much root does it have? But like I say, at this point, after all we've done, I think that's still an ideal, but we haven't figured out which plant is the one to put in there.
And what we found with clover, while it had so many positive attributes, the voles were the problem. They came in one winter and literally Ate all the clover we had planted, and it was planted right up to the trunks. That entire strip, like I say, maybe a meter and a half wide, was planted to clover. It was completely obliterated over winter.
We were lucky in that they didn't eat the trees, but it turns out white clover is one of the most preferred food sources for voles, and therefore it's just too high of a risk for our commercial folks, for sure. For a home gardener, home grower, it might be Less of a problem, but it made me back away from it.
So finding that plant that It really hits all those things. We want it to suppress weeds. We don't want it to use a lot of water and nutrients. And we don't want it to attract voles. In fact, it would be nice to find a plant that would repel voles. And so there's been some work and some interest in that, but we're definitely not there yet.
[00:17:41] Listener Questions and Expert Answers: How much mulch is too much, nitrogen immobilization
we've got another really good question from John. John is in Ontario. Okay. So John writes, how much nitrogen is consumed in the decomposition of wood mulch? Is this an issue or do the benefits outweigh the negatives? I love that question because, here in Ontario, and I think everywhere, trees, whether they're fruit trees or other trees, you've got, beautiful, I don't know, cedar or some hardwood mulch chips around the tree.
It looks pretty. It protects, from weeds. But I remember hearing that, wait a minute, again, if you have a young tree, as these chips decompose, they start taking nitrogen out of the soil rather than putting it in. And that would be, me making nitrogen less accessible to the trees. So how would you respond to John's question?
Are you losing nitrogen by mulching with wood mulch? in our experience, the answer is no. Because when you put the mulch on the surface, you're not incorporating it with the soil. And so it's very different than if you dumped on four inches of woodchips and rototilled it in. That would be a train wreck from a nitrogen standpoint.
But when it's sitting on the surface, the interaction with the wood chip in the soil is in a fairly narrow zone. And so the bulk of the soil is not being affected by the. By the woodchips in terms of nitrogen. It's above the soil. There's decomposition going on there. You'll get some of the nitrogen that's released in those chips, which can take a while.
It will work its way down with water, as rain or irrigation. But we've also seen tree roots very consistently grow from the soil up into the mulch. And we assume they're searching out nutrients or other factors that we're not totally clear what they are. But we have seen where we've used the woodchips.
And we've monitored the tree nitrogen by taking leaf samples in July. Oftentimes, the, The woodchip trees will decline very slightly from other trees without the woodchips in terms of nitrogen, but they'll grow more. They'll have higher yields. Now, over the long term, I think that's something you'd want to watch, and you might simply correct it.
by adding a little bit more nitrogen fertilizer to the system and compensate for it. But over time, a lot of those woodchips will be decomposing, the carbon will go off to the atmosphere as CO2, and the nitrogen that's in there will become slowly available. And also you talked about your trial with woodchips, that was a three year trial.
So even if in year one, the woodchips were at their stage where they were, Starting to take nitrogen out of the soil and away from the trees, maybe in year two, they go into the next phase where they start to release that nitrogen back into the soil. maybe the first year you pay your price, but then after that you just reap the benefits.
we just even haven't seen big depressions in year one, because as I say, if the mulch is on the surface, the woodchips are on the surface, there's not that much interaction with the soil. Interesting. That's the secret. Cool, that's great. The other thing is, you talk about, in my book and in my online course, I talk about the far too many mistakes that I have made in growing fruit trees and the lessons that I've learned.
And one year in our orchard park, we did mulch our trees. I can't remember if it was with woodchips or something else, but we put way too much mulch. And, I think we paid the price. I don't know if, can the tree roots still get oxygen if you put a lot of woodchips on top?
It probably depends on your soil type. I have seen situations with a fairly high clay soil, which we do not have here in Washington, so this is not an issue for us, but definitely it is in other areas. And I've visited sites where they put on a fairly thick layer of woodchips, four inches or so.
Over the winter, the soils had become saturated and they definitely became anaerobic or sour. And, it was not a good situation. yes, that, that can be an issue if you don't have good drainage. isn't that interesting? And we got an email from Anthony. I think Anthony's in Baltimore. And he said here, David mentioned that applying mulch four to six inches.
Is a good idea. Is this the ideal depth or can two to four inches work as well? So again, the answer is it depends on your soil and it's about really learning, learning what your, the needs of your trees are. We have, it depends on your goal as well. And so my evolution on the mulch is how little mulch can we put on to get some of the, these major mulch benefits because we started out.
Wanting to suppress weeds and you need a very thick amount of mulch to have any chance of doing that in many cases Even four to six inches did not give us great weed control for very long But we often saw these benefits in terms of tree growth and proof for yield fruit size So I started to think well, geez, maybe weed control shouldn't be the primary focus and We need to complement other forms of weed control with a mulch, but if we could get 80 percent of the mulch benefit from an inch of mulch, particularly when we're trying to do this on large scale orchards, that might make a lot more sense.
And I think that's the direction I'm heading myself, is thinner mulch layers, but knowing that you're going to have other sorts of weed control. Interesting. And again, if it's a backyard, a few trees in your backyard, that's a non issue. So then in that case, for sure, I would say you don't need four inches whatsoever.
That's renewed on a regular basis, so you keep about an inch on the surface, probably would be perfect. Oh wow, that's great. So we've got an email from Stan, and Stan says, Who knew? So much info. Listening from NYC. So that's from Stan, and we've got Hannah wrote, Hi Susan, thank you for a very enlightening show.
I've learned a lot. Wow. And it's only the beginning of the show. So John writes us back saying, thanks for the reply. Good answer. This is something I've heard but never really heard a response to. So glad to hear that mulching with woodchips is not really a nitrogen consumer. So John is from London, Ontario. So another mulch I want to talk with you about is actually taking the prunings.
[00:24:10] Pruning and Mulching Techniques
from your fruit tree. So you're pruning your healthy fruit tree and mulching it up and putting it around the tree. Tell me about that. Do people do that? Is that a good thing? Yeah, that's something that's become of interest here lately. Historically, what people have done is they take their, they prune their trees and in the old days they would rake the prunings out and they haul it out of the orchard and burn it.
in probably the past 20 or 30 years that, because that was a lot of work, people had a tool called a flail mower that they would break the prunings out into the alley where they could drive a tractor and they would run this flail mower which would just basically shred them in place and leave them right there in the alley.
So that was a lot easier, job done, no problem.
[00:24:58] Innovative Methods for Reusing Prunings
But we got to thinking several years ago that really that carbon is in the wrong place. That's wonderful carbon from those prunings that we would like to put right back over the roots. And so now people have tried to take that and mechanically move it back onto the tree row.
And there's a couple of different ways I've seen it done. One is using a brush rake and a brush rake is a tool that the orchard is used to get the prunings out to flail them in the first place. They can reverse the belt on that and it sweeps the material, the chips essentially from the tree row, from the alley back onto the tree row.
So it's a very simple way to, to put that material back over the roots. So the second way there is a flail mowing machine made in Italy that we've. There's a couple of people here that have bought them now. They will take material in your alley and it could be your prunings. It could be a very tall cover crop that you're growing and they'll chop it up.
And rather than just dropping it in the row, where you're driving, they'll blow it onto the side and right onto the tree row. So there's a couple of different. possibilities there. But what is it? and even by the way, what we do is we take our, in our little orchard park. So we take our young clippings from our tree that we're removing as we do our annual pruning, and we just cut it into little one inch pieces and throw it around wherever, whatever we've mulched the tree with.
But I don't know if that would break down. Maybe you can comment on that.
[00:26:28] Benefits of Young Growth Mulch
But what is it about the young new growth that is good for your tree? it's a mulch material that's right in the orchard, so if you're not thinking about whether it's the new prunings or the older material, it's just the fact that it's woody material that's already in your orchard, you don't have to haul it in.
So if you've got 10 acres of orchard or 100 acres of orchard and you want to mulch, you're talking truckloads and truckloads of material. So the more of it we can source from within the orchard, the better. It's a locally recycled material in a sense. But the second thing is, that particular material, if it's the smaller wood, It's nutrient composition is very similar to what you're going to grow again this year and next year.
That's what, it is. It's the same nutrient content as, what your tree is going to need in a sense. It contains that same balance of nutrients versus the stem wood. big wood is going to be quite a bit different, chemically than that young wood. And there's been some work done on this up in Canada, where they looked at what they call the ramial woodchips.
And that's the term that is used for these below a certain diameter. they decompose differently. They support different fungi in the soil. And as I say, their nutrient composition is a bit. different than the larger, older, stem wood. So when people talk about ramial woodchips, and you can read about it in Michael Phillips book, he's got a book, I think, called the Holistic Orchard.
he's got lots of interesting books. He talks about ramial chips. woodchips. And so basically that's what you're talking about that young, those young clippings from your trees that you're removing anyway with correct pruning and it's, it has to be decomposed, in order to be considered ray woodchips.
no. It's just, it's really a size, description which relates to age. So it, typically is below so many centimeters in diameter, and that typically is gonna be one to 2-year-old growth. Okay, that's great. So no, when they're putting it on, it's simply chipping that material and putting it around the trees.
And so will decompose from there. And so for the backyard orchardist or people like a community orchardist like myself, if we take our young prunings and we cut them into little one inch pieces, do you think somehow eventually those will decompose or is it just too big to be useful? They will eventually.
And if you had a chipper, that would even be better. Just a little garden chipper would do the job. But it's interesting. I put on probably four to six inches of mulch and then renewed it in an experiment that I had. So I put it on the first year, put some more on in the third year. Six years after I had done that experiment, I came back and I could not find one single piece of mulch on the soil surface.
Every bit of it had gone into the soil or decomposed, which was pretty remarkable. So the soil organisms will make that stuff disappear as they decompose it and work with orchardist I know, He's having a heck of a time keeping a mulch in the orchard because his soil literally digests it so quickly.
That's incredible. That is incredible to think of those little tiny creatures and how they can, pull apart all this organic material. That's quite amazing. Yep. And process it. when you shred it finer, it's easier for them. So in some ways, if you want the mulch to be more durable and last longer, then bigger chunky chips is a better option.
But if you want the quick turnover, then But the more finely shredded material is, we'll do that. Amazing. Now we got a great question from Nan, Nan is in Orlando, Florida.
[00:30:19] Mulching Tips for Different Climates
So she says, should we always mulch trees, new plantings, established trees? That's a really good question. How would you respond?
I would probably, I'd want to know a bit about the, the soil in that site. As I say, if it's a very high clay soil, I would be more careful if I was in an environment where the soil conditions were more sandy and it was a hot environment in the summer and maybe not so rainy and drought conditions are a problem.
Mulching, mulching the young trees is fantastic. It just evens out the moisture so you don't get periods of moisture stress, which can be really, hard on young trees. We're also finding there are temperature effects that soil can get too hot for root systems and tree fruit, tree roots, some of them, particularly the dwarfing roots of apple.
There's some evidence that they don't like as high a temperature as say a big old standard tree does. So I think there's a combination of both some moisture buffering and temperature buffering that goes on when we put a mulch on. And so in an environment like Florida, where hot temperatures are very likely, it could give you a benefit that way as well.
Very interesting. I would be careful, though, if there are disease issues, that, like I say, for us here in central Washington, in a very dry climate, we don't have to worry so much about disease, but in more humid, hot climates, That would be my first question. What are the disease risks that I need to be thinking about?
Because that could come back to bite you. And well, one of the things that I was thinking about is if you're pruning a fruit tree and the fruit tree is diseased, you don't want to clip up your young growth and put it on the soil because that would be spreading the disease. So that's something to consider as well.
Correct. It depends on the disease, but absolutely. That's right. Now we've got an email from Kyle. Kyle is in Winnipeg. Is just regular sawdust a good mulch? I have tons available for free. Thank you. Yeah, sawdust to me is very different than the woodchips because it's got that small particle size.
It's probably going to react and tie up nitrogen a lot faster than you would get from the woodchips. It's also going to be, Oh, I don't know, chemically a bit more homogeneous, whereas if you've got ground up whole trees, you've got some of the young wood, you've got some of the bark, it's a bit more diverse material.
Whereas the sawdust is pretty much strictly that's very mature stem wood, there's nothing else in it. I would typically avoid sawdust for fruit trees. Of course, the berry people use them and they're trying to do some other things. But, for me, that would be a lower choice. I might look at bark, which is often a waste product from sawmills.
some folks in New York did a lot of research on bark mulch. There's where hardwoods, softwood bark might need to. have some aging going on first, but that might be a better choice than the sawdust. Okay, I've got an email as well, that I got here from Dom. Now, where's Dom from? I'm not sure. He says, we, oh, Don, we use compost and ray meal chips.
We've been using Comfrey and Baptisia. Baptisia, I think that's what it is, under the trees. Bush cherries in between trees. And last year around a few pear, cherry, and apple trees we put lemon balm, echinacea, chives, and some herbs.
[00:33:52] Living Mulch and Pest Control
So how do you feel about people, I guess they consider that living mulch, using herbs, using comfrey between trees, in addition to their compost, ray meal chips, woodchips, whatever.
Yeah, I think particularly once your trees are established, experimenting with those sorts of things are definitely worth doing, seeing what seems to give you a benefit. Sometimes you might be getting plants that are, positive from a pest control standpoint. Some of those may deter voles. I don't know.
We've had some experience with sweet woodruff and thyme as being less attractive to voles or even more. Perhaps being a little bit repellent. So yeah, I think that those have a fit, particularly at a smaller scale. But just watch the competition and the habitat for the voles, those are the two biggies, I think.
I want to talk about voles. Oh, first we've got another email from Frank. Frank says, Hi Susan, love your guest. This is a big compliment, David. love your guest I want to talk about voles. Let's do that. So David, I've gotten emails about, voles as well, people saying, Oh my gosh, I can't even put mulch because I have vole problems.
[00:35:11] Voles and Mulch: Risks and Solutions
Tell me about voles and their relationships with mulch. Voles like two things. They like a place to live, protection, habitat, so to speak, and, food. That, those are the two big things you're, trying to figure out in an orchard environment.
And if you put out any sort of, practice like a mulch or a living mulch that provides them cover or protection, they aren't going to get affected by the predators so much, particularly the raptors, the hawks and whatnot. They're a big one. They can't see them, so they're free to go around and reproduce and produce, I don't know, five, ten.
we have seen some really bad vole problems with mulching, but it depends on the kind of mulch. not all mulches are created equal, but yes, mulches can be a major risk for voles. And what we've seen, and this has been very consistent, not just here in Washington, But with people using mulches in other regions, they do not seem to like these big, chunky woodchips of all the mulches.
That seems to be the one where we don't, observe the vole activity or vole populations going up. And I actually did one experiment where we compare it, a wood chip mulch in the tree row, like standard thing for some. Four or so inches thick, with a totally bare ground, with a tilled tree row disturbance, and no significant difference between the woodchips and these other bare ground treatments.
Where we had living mulch in the tree row in that same experiment, tremendous increase of vole presence. Compared to the bare ground or the woodchips, but one of the living mulches we tried was this Sweet Woodruff (Galium odoratum), and it was significantly less than the other living mulches, whether they were grass or legumes, but still more than the woodchips or the bare ground.
And so in a more recent trial, the same thing was tried, also tried thyme in the tree row. And again, while it was better than others. And we did get a reduction. It was still too much tree damage to tolerate. So of the inert mulches, things like straw or the weed fabrics. Particularly the weed fabric is a terrible, situation for the voles because they love to get right under it and they're totally free to roam anywhere around, go right up to the trunks, chew on the bark.
Complete protection. Straw mulch is pretty much the same sort of a thing, At this point, the one inert mulch that we've had good luck with has been these big, chunky woodchips in terms of not creating more of a vole problem. I can't say never, that you'll never have a problem, but this has been observed enough that I feel like the risk is low, but of course that's different than zero.
Now the voles can actually kill the trees, can't they? What do they do? They nibble on the bark and Yes, they girdle the tree. Yep. So that's a big danger if that's a problem in your community.
[00:38:25] Proper Mulching Practices
I also wanted to talk about an experience that I had in one orchard that I helped out with where I taught them how to mulch and I taught them about mulch sort of circles where you've got a donut of mulch around your tree and you do not pile the mulch right up to the trunk of your tree.
they did a beautiful job mulching. They forgot that little part. So they packed their beautiful mulch up to the trunk of the tree, and the next time I came back, the insects had gotten into the mulch and started eating their way into the tree. So can you, address that? How you're going to lay your mulch, how far it's going to be from the bark, and what insects could be a problem?
here, we don't have those borer problems that you might be referring to, so we're fairly lucky. you can get sucker growth in some cases, depending on how your trees are grafted and what not, by putting on trees. Too thick of a mulch. But I would say in general, when people have a few trees that they're working with, yes, what you're describing is right.
You want the mulch on there and to basically have a taper off to a very thin layer right as it touches the trunk. Okay, so that's good. So now we have an email here from Rosemary. Rosemary writes, I'm writing from Baltimore and have been part of the Baltimore Orchard Project.
[00:39:43] Managing Clay Soils in Orchards
Could you go into more detail about clay dominant soil and orchard tree soil?
What are some suggestions to support a healthy environment for this depleted soil? So she's got clay soil that is depleted. Our trees are about three years old. So Yeah. one thing that is done where you've got very high clay soils, and this may be too late if they're all planted, but they will create a berm and perhaps they would incorporate into that berm some organic material, some compost or other material to help counteract the negative effects of the clay, particularly physical effects, and you get a little drainage that way.
The water can get out of that berm and down into the area between the rows and away from the roots. that's. used in a number of countries commercially, where they've got very heavy clay soils. So that's a strategy that I've seen, and the otherwise adding organic matter to clay soils is your, it's one of the best things you can do.
The best bet. Yeah. So in a sense, the organic materials, they will take a soil. If your two ends of the soil texture spectrum are clay on the one hand and sand on the other, they're very different. Issues when you're at those two ends of the spectrum, but adding organic material for both of them brings them closer to the more ideal silt loam kind of a texture in the center.
So either way you come out good, whether it's a real sandy soil or real clay soil, organic matter is fantastic for you. And that's beautiful because it brings us full circle.
[00:41:16] Compost and Mulch: Best Practices
In the beginning you had talked about using compost on your fruit trees. Sometimes it can give you a little bit too much nitrogen.
what we do in our orchard park is we use our compost early in the season before flowering time. We put a beautiful layer of compost, not too much, maybe one to two inches thick around our fruit trees and then cover it up with a different type of mulch like woodchips. but then in the early spring, they, it gets the energy when it needs it.
But I haven't seen any extra growth by late summer. I would assume most of the nitrogen has, has gone from that, nice organic matter. Would you, have any comment on that, David, or? it's hard to say without knowing what type of compost. I think people Often believe they're getting more nitrogen from the compost than they are.
At the time of application, this is a really common problem that we see. And then they see a bit of nitrogen shortage, so they pour more compost on. But then over time, it starts to release and they can't turn it off, so they end up in trouble. So that, the compost is trickier to work with. That's one of the challenges, that's why synthetic fertilizers were invented in a way, because you can control them much better.
So you have to understand your material. And really think about the timing. And almost anticipate if you want the nitrogen available at this date, you have to back up and say, what's the, what are the temperatures going to be when I put the compost on? About how long will it take to mineralize or release that nitrogen?
And will that timing sequence be right for when you want it available for the tree? So you have to do a bit more anticipation. Wonderful. that's yep. That's good advice. And I think in my book, I talk about how you can look at your tree and you can see how much, how much nitrogen it has.
Does it need extra nitrogen? There's so much to learn, but believe it or not, the show is over.
[00:43:14] Conclusion and Resources
But it's been so wonderful having you on the program. great questions from the listeners. I hope this is helpful, and I've got a fair amount of information on my website that we can get to people if they're interested in any more, but yeah, we're still learning.
What you told me about the fellow from England with the Willow Chip mulch. very interesting. There's a lot more potential to mulch that will be discovered. Yes, and hopefully I'm going to cover that on an upcoming show, so everybody, wait to hear. When you hear about a willow mulch program, you must tune in and, Learn lots more.
so David, thank you so much. I, we will speak again. I so look forward to that. And, I'll talk to you soon. Happy spring, everybody. Happy spring. that was Professor David Granatstein. He's with Washington State University and it was so fun having him on the show. the program is basically over.
That's it for today's episode of the Urban Forestry Radio Show. Did you enjoy the show? I hope so. I have lots more information to share with you on my website, orchardpeople. com. I have blogs and videos and archived episodes of this podcast with lots more information. Now, if you want to up your game when it comes to fruit tree care skills, you may be interested in taking my online course.
It's suitable for both beginner and intermediate level growers, and you can find it at orchardpeople. com slash. You're listening to the Urban Forestry Radio Show on Reality Radio 101. I'm Susan Poizner from OrchardPeople. com. Thank you so much for tuning in. And I look forward to digging into a new fruit tree care topic with you next month.
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Thank you for listening to the Urban Forestry Radio Show with your host, Susan Poizner, right here on Reality Radio 101.