GB 112 TRANSCRIPT Does Mulch Rob Soil Nitrogen? Soil Solarization.
24:28
SPEAKERS
Debbie Flower, Farmer Fred
Farmer Fred 00:00
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Farmer Fred 00:20
Welcome to the Garden Basics with Farmer Fred podcast. If you're just a beginning gardener or you want good gardening information, you've come to the right spot.
Farmer Fred 00:32
Making the rounds on gardening pages on social media lately, are stories about how mulch will rob your soil of nitrogen. Hmm. College horticulture Professor Debbie Flower retired and I do a deep dive into the mulch pile to explore that rampant rumour. Also summertime is soil solarization time, a great way to rid your garden soil of pests or a quick way to kill off a portion of your unused lawn area, in preparation for a new garden bed. We talk sheet mulching as well. It's all about the soil here. It's on episode 112 of the Garden Basics with Farmer Fred podcast, brought to you today by Smart Pots. And we'll do it all in under 30 minutes. Let's go.
Farmer Fred 01:19
We like to answer your garden questions here on the Garden Basics podcast. I'm joined in the studio today with Debbie Flower, retired college horticultural Professor. Debbie, what are you growing this year that you haven't grown before?
Debbie Flower 01:31
That I haven't grown before? Well, outdoors? Probably nothing. Nothing new. In my greenhouse, I have some Joshua trees I started from seed. And I have some lychnis coronaria which I've grown before. Yeah, what's its common name? Good question.
Farmer Fred 01:49
Lychnis. Yes.
Debbie Flower 01:54
Which I have in my yard. I always... Rose Campion.
Farmer Fred 01:58
Didn't she dance with Gower Champion? Yes, of course.
Debbie Flower 02:03
My mother always used to grow it in our garden in New Jersey as an annual. Here in our warm climate, it is a perennial, and it will seed around quite a bit. It has very chartreuse flowers and grey green leaves, so it's a very interesting addition to the color in the garden. But it seeds around. And a whole bunch of it came up in a pathway. So I scraped them up from that pathway and planted them in pots, and some are taking and some are not.
Farmer Fred 02:33
And these are low water use plants.
Debbie Flower 02:36
They can be. When you're choosing water wise plants, there are some characteristics that you can look at a plant and say that one will be water wise, meaning a low water use plant. And though one of those characteristics is if it's gray. If the leaves are gray, they typically have some coating or hairs on them which reduce water loss. If it is hairy, hair will slow down the ability of air movement, wind to remove water from the surface of the leaf. And these are gray hairy plants. So yes,
Farmer Fred 03:11
That's a good thing. And we bring this up because we have a question via Speakpipe. From Eileen and let's hear what Eileen has to say because she's rather concerned about what a lot of us here in California and the southwest and even into the Midwest are concerned about this year. And that's a drought.
03:27
"Hi Farmer Fred. I live in California and everyone's talking about the drought. I know that mulch is one of the best things you can do to conserve water in your soil. And I've even heard that a really good thick layer of mulch can cut down the water you need by like 40% which is amazing. But I have some concerns because I've seen some stuff fly around on my Facebook gardening groups that mulch will actually suck nitrogen out of the soil, which would be really bad for my vegetable garden. So I'm curious, can you set the record straight? Is it true that mulch will actually tie up nitrogen or suck it out of the soil? Thank you so much."
Farmer Fred 04:06
The problem actually is going to a Facebook gardening group. Yes. That's, that seems to be the brushfires we've been putting out for the last few years. Yes. Ask any garden commentator like us and it's like dispelling these myths. Yeah. And that's not a myth as far as sucking up nitrogen, but we'll get into that in a sec. Okay. By the way, just let me say that Eileen got in with her melodious voice via Speakpipe and you can too, leave a question for us at Speakpipe. No phone to call. You go to Speakpipe.com and type in gardenbasics. And you, too, will be able to speak into whatever device you just logged on to and leave us a question just like Eileen. Now if you want to call us, you can. The phone number 916-292-8964. Wait for the recording. 916 292 8964. text us at that number as well. 916-292-8964. or email Fred at farmerfred.com. That's how you get in touch with us here. Meanwhile, Eileen is worried about mulch and the fact that mulch might be sucking nitrogen out of the soil. Depends on where you put that mulch.
Debbie Flower 05:23
Right, that's a common concern. And there has been scientific research done to check that, if you just lay the mulch on the surface, there's not a problem. The things that are going to draw nitrogen out of the soil are things that are high in carbon. So wood products, you can use wood products very safely, conserve water in your landscape, reduce weeds in your landscape, moderate temperatures in the soil, without having nitrogen drought, or nitrogen draught, as it's commonly called, occur. If you till in that carbon or wood product, that's when the problem is going to occur. It occurs wherever the nitrogen is drawn, yes, it is drawn into the mulch, but it's drawn just from where it touches the soil. And so if it's just laid on top, there's just that one connection, if you till it in, then there's soil all around that piece of mulch. And the nitrogen is needed by the microorganisms that break down the mulch, they feed on the nitrogen from the soil, and then they break down the mulch and release more nitrogen. If that process is happening only at the surface of the soil, everything stays in balance. If you till your high wood product, high carbon product into the soil, then there's so much more exposure of that wood to those micro organisms, they work from all different sides, and they need more nitrogen out of the soil. So the trick, it's not really a trick. It's even a lazy gardener technique. And I am a lazy gardener, is to just lay the mulch on the surface. It does all those wonderful things, but it does not take too much nitrogen out of the soil. In fact, ultimately it adds nitrogen.
Farmer Fred 06:56
So for those gardeners who might be listening, and are thinking, "Oh my, i just tilled in a bunch of bark. What do I do now?" Can adding fertilizer that has nitrogen in it alleviate that?
Debbie Flower 07:09
Yes, it can. Nitrogen, you can use a solid source like chicken manure. Be prepared for visitors like cats and skunks and things, or bloodmeal or bat guano. You could lay that on the surface. Or you could use a liquid version of synthetic fertilizer, but you don't need a lot. It doesn't need to be a high quantity of nitrogen. And nitrogen moves very quickly in soils with water and it moves in the air as well. So if I realized, first of all, if I tilled it in, I would plant something that germinates very quickly. Radish would be one thing and see how it looks. If it's very yellow, yes, you have a nitrogen deficiency and you need to add fertilizer for that. If I don't have a problem, I'd leave it alone.
Farmer Fred 07:54
Yeah, radishes are fun too. You can get the whole family involved in that because the little ones like to watch the radishes grow because they grow quickly. Yes, like within a week probably you're gonna see something, right. And what, you can harvest radishes within 35 or 40 days, very quick crop.
Debbie Flower 08:09
I always forget to go out and pull them. I leave them and let them flower and then I get beneficials that come and feed on the flower so you can go that route, too.
Farmer Fred 08:17
Exactly. So basically, you just want to lay the mulch on top of the soil and you'll be fine. And now what about something other than wood chips, wood bark, Chipped/shredded tree parts? If your idea of mulch might be, say, compost?
Debbie Flower 08:34
Yeah, compost typically is very well broken down already. And so that breaking down process which involves the micronutrients that have to have nitrogen to live is not happening or not happening at the same rate as it would be happening with arborist chips. I use arborist chips all over my yard, not so much in my vegetable garden but all over the yard and there are parts of the vegetable garden that have them and have no problem at all. Compost has already broken down the micro organisms, have already chewed it all up and released the nitrogen. In fact, compost tends not to be very high in nitrogen, unless you've got pretty fresh, like compost from a cow pasture or something.
Farmer Fred 09:15
Well, yeah, that and a lot of people do use manures horse manure, steer manure, chicken manure, and but it's always a good idea to let it sit in a pile for a while.
Debbie Flower 09:23
Right, let it age. It can be too hot, meaning has too much nitrogen in it. Yeah, the one type of mulch, if you know a woodworker and they have piles of sawdust and they want to get rid of it, it can be turned back into organic matter for the garden. But if you put it directly on the soil, it is so fine that you have greater exposure of the wood to the microorganisms and that is the one situation where you might have nitrogen draught by just laying it on the surface.
Farmer Fred 09:52
if it's just sawdust. Exactly if you put on sawdust too thickly or pine needles too thickly around your acid loving plants, your azaleas, rhodos and camelias. You could end up with an anaerobic environment, meaning air and water can't pass through.
Debbie Flower 10:07
He's right. Even grass clippings are like that.
Farmer Fred 10:10
Yeah. Compost, too, has the drawback, if you're using it as a mulch, of being a great haven for blowing weed seeds, and can take root very easily in that way, it's a little more difficult. If you're using bark, or other wood products. One mulch you don't want to use even though it's organic, are rocks, Mm hmm. Because rocks don't break down. They don't feed the soil. That's one of the major benefits of putting down three inches or so of mulches as it breaks down there. It's feeding the soil. It's improving the soil biology, but rocks break down very slowly,
Debbie Flower 10:46
Very slowly, very slowly. Now, they are used extensively in desert environments. Yeah, they're there. They're brought in and they're laid purposely. And that is strictly to not have anything grow. The very first time I lived in the desert, I was so amazed...
Farmer Fred 11:05
Were you on a horse with no name?
Debbie Flower 11:07
I was so surprised, I'd come from New Jersey and I moved to Arizona, that if I was so surprised in the in the desert, if you don't plant it, it doesn't grow. Whereas in in places with rain, yeah, things grow, things grow. And you have to go out and pull them out if you don't want them. Now, there are a few weeds, but you have to irrigate that space, so that it's just a covering of the soil. And I don't think it has any purpose except to prevent dust.
Farmer Fred 11:33
I've seen test results about the thought that the rocks on a hot day will transfer that heat to the root zone of the plants. And according those test results, It's not necessarily true that that happens if the roots are deep enough, right. If it's a very shallow rooted plant, I think that might be an issue.
Debbie Flower 11:53
And that would be just at the beginning because the plant will change where its roots live, the roots that are getting too hot will die and the roots that are deeper and stay cooler will live and so it'll readjust. Yes, rocks heat up when you don't want to touch them in the middle of 100 degree day, but it takes them time to heat up. And that takes some time to cool down. So they're just sort of shifting compared to bare soil.
Farmer Fred 12:15
They are shifting when the roots would be hot. My loathing of rocks as mulch goes back to when I was a child and the only money I could make in the neighborhood, besides cutting lawns, was pulling weeds. And this one neighbor had a completely rock front yard in Southern California, and a terrible infestation of oxalis. I just remember kneeling on rocks all day and pulling up oxalis and bur clover, it was just no.
Debbie Flower 12:44
And if you decide you want to garden in that spot, plant something, you've got to move those rocks, right. Whereas if you have mulch, you just sort of scrape it away and it moves easily and you can dig your hole. But if it's rocks, it's not so easy.
Farmer Fred 12:57
There is one downside to using bark or wood chips or arborist clippings for mulch. And that is the fact that native bees which like to nest in the ground can't do it in mulch, right. So keep an area bare around the trees, because there's usually little culverts around the crown of the tree where the roots meet the stem that they can nest in. So if you keep that free of mulch, the bees will be happy, in that regard.
Debbie Flower 13:24
They like sandy soil. I have left a low mound unmulched specifically for them and nobody's come. But I was visiting an Iris garden, and part of it was in lots of sand, the soil was very sandy. And the bees were coming and going as I'm walking through the garden under my feet. So they have some particular soil preferences.
Farmer Fred 13:48
Yeah. And anyway, if you're putting down mulch, you want to keep it away from the trunk, absolutely. Keep it away from existing trees and shrubs by two or three inches too, because you don't want to suffocate that crown area. Right. And by the way, for those of you that live in parts of the country where mulch volcanoes are common, I guess in the winter, it's okay, but you need to clear it away as the weather warms as well.
Debbie Flower 14:11
You certainly don't want it to get wet and trap moisture against the trunk of the tree in warm weather, then you're going to allow plant killing funguses and bacteria to live there and you're going to lose your plant.
Farmer Fred 14:22
A mulch volcano is where you pile up maybe two feet worth of mulch around the tender plants like maybe rose bushes or something like that. But like you say, that can have the deleterious effect of rot if you don't clear it out.
Debbie Flower 14:38
Right. But in winter, if it's a very cold place, say up north Minnesota, something like that, and you have a rose, you do often bury it in mulch, and that is to keep it from drying out. When it dries out, it is much more susceptible to freezing and dying. It can just die from the drying out so you're covering it up to protect that.
Farmer Fred 14:57
Alright and then remove it as the weather warms.
Debbie Flower 14:59
Yes remove it as the weather warms in spring.
Farmer Fred 15:06
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Farmer Fred 16:05
Let's get back to our chat with retired college horticultural Professor Debbie Flower. We've been talking about mulch. Now let's talk about soil solarization, perhaps using mulch, perhaps using clear plastic...
Farmer Fred 16:20
There are other ideas for mulch of newspapers, cardboard, using cardboard is a great idea for killing off a lawn, let's say you want to convert it to a garden. If you just mow that lawn really short, put down cardboard, put down a few inches of a coarse mulch, like chipped shredded tree parts. Couple weeks later, you probably have a deadline, you can plant right through that cardboard, and that cardboard will break down eventually,
Debbie Flower 16:46
Eventually. But consider, and we all have lots of cardboard, probably because we've been ordering things to come to our house instead of going shopping. That cardboard is made to handle being in the rain, being carried and thrown, and so it's often coated in a plastic. And that can take some time to break down. I've used cardboard in a pathway where I just laid it and overlapped it and put bark mulch on it. And I used it on a property where the front yard was weeds. And we laid a lot of cardboard down and then put mulch on top of it. And it takes almost a couple of years to fully break down.
Farmer Fred 17:25
Alright, what about one strategy of perhaps moistening it thoroughly?
Debbie Flower 17:29
Yes, Yes, we did. We did moisten it thoroughly. And that's a hard job. Actually, if it's got this wax on it, there are some horticulture professors who really dislike the idea of using cardboard as a sheet mulch in the landscape because of that wax coating. And I don't know what wax coating is made up. If you are going to use the cardboard, take off all the tapes and things, staples, because they'll just show up later in your garden in a place you probably don't want them. Use it in a place that you don't need to plant in immediately. And give it time to break down.
Farmer Fred 18:06
Yeah, I wonder if you broke open boxes and let them sit in the sun for a while and then use them as mulch.
Debbie Flower 18:12
That's a good idea. Yeah, the wax would probably break down in the sun. Yeah.
Farmer Fred 18:17
But yeah, sheet mulching is very popular, especially in areas of drought, where one of the strategies for using less water is, do you really need all that lawn? Maybe cut it in half and one way to get rid of that lawn is doing sheet mulching, you can find instructions online on how to do that. I'll have a link on today's show notes about sheet mulching. The other option, especially during June, July and August is soil solarization, where you're putting down clean, clear plastic over your lawn area after you've mowed it really, really short. And you've watered the area really really thoroughly so that the moisture gets down 12-20 inches or so. And then put down clear plastic secure all the edges so no air can get in beneath it.
Debbie Flower 19:00
That's critical. Yeah, and you can't just use bricks or something, you have to make a little trench, lay the plastic in the trench and then cover up every single piece of the edge.
Farmer Fred 19:10
You've got to trap the heat. We're talking clear plastic of two mils or less as far as thickness goes. One cheap alternative is head to your big box store, the Lowe's or Home Depot and get a roll of painters' plastic that will work and you leave it secured on that area for four to six weeks. And that can actually sterilize the soil down to 12 inches or so. Temperatures get up to 140 degrees. Besides killing the lawn and kills weed seeds, it can control nematodes, and in one study I read it talked about how after soil solarization it actually improves the nutritional quality of the soil.
Debbie Flower 19:52
Oh, I hadn't heard that one.
Farmer Fred 19:54
Yeah, they've found in tests that they've done that it actually improved the nutritional aspects of the soil. And don't worry about earthworms or mycorrhizal fungi, or bacteria, they they move out, they move out. And they reproduce quite quickly too, in that situation. But I think really the key besides anchoring down the clear plastic for four to six weeks, is to thoroughly moisten that soil. Yeah, because that helps move the heat downward. Yes, I've done that in areas of Bermuda grass and knock on wood. Bermuda grass never came back.
Debbie Flower 20:29
Whoo. That's impressive. Yeah, yeah, that's really impressive.
Farmer Fred 20:33
But after we solarized that area with the clear plastic, we put down two inches of compost, then we put down three inches of mulch. So try to get through that Bermuda grass. Yeah, it will. I'm sure it will.
Debbie Flower 20:47
It comes into my yard from the neighbor. And yeah, it can come up through amazing stuff. But that's wonderful. . And I imagine the increased nutrition might be due to the dead roots. Grass has more root per area of above ground parts than any other plant. And so you have lots of organic matter automatically in the soil if what you're solarizing is a lawn solarization, it will only work if that area is in full sun.
Farmer Fred 21:15
Again, though, there are all sorts of great benefits to mulch. And Aileen, I'm glad that you want to use mulch because it retains moisture, it keeps soil temperature constant, it reduces plant stress, it suppresses weeds, it gradually increases soil organic matter as it breaks down. It attracts beneficial organisms that improve soil fertility and porosity. It encourages healthier plants. It reduces the needs for pesticides and fertilizers. You and I know gardeners who, when it comes to their fruit trees, mulch is their sole source of fertilization.
Debbie Flower 21:47
Absolutely. It works very well.
Farmer Fred 21:49
It protects roots and plants from mechanical injury. If you think about it, if you don't have grass growing right up next to the trunk of your trees. That means there's less chance of you getting too close with that weed whacker or lawn mower and damaging the bark of the tree. So it's great. And plus on hillsides and around homes, it can suppress the spread of brush fires. Now, one warning in that regard, is that a lot of Fire officials, especially here in California, advise not putting mulch next to the foundation of your house, keeping the area clear, because that mulch could smolder and set a shrub on fire that could go up into the eaves.
Debbie Flower 22:27
Right. So if you are in a place that you need to be worried about wildfire, there are lots of things you should not have close to your house. One is that shrub and another is that maybe planting a lot of succulent plants. Succulents are plants that take water when they can get it and store it inside of them and they're often very thick. They may be cool to the touch. Cactuses are succulents, Jade plants are succulents, geranium are succulents. plant those things closer to the house so that there is a little bit of protection. There's whole list. There's lots of information out there about fire proofing, or landscaping for fire suppression.,
Farmer Fred 23:08
Well, it's easy to go off on a tangent when it comes to mulch, it's because it is so valuable and it should be part of everybody's landscape. Mm hmm. All right, Debbie Flower. Thanks for your help on this.
Debbie Flower 23:19
My pleasure. Thank you Fred.
Farmer Fred 23:20
And thank you, Aileen, for sending us that question via Speakpipe. And again, you can do the same thing. Go to speakpipe.com, type in gardenbasics (one word), and you, too, can yell at your computer at us anytime you want. And of course you can always call 916-292-8964 you can text that number as well. 916-292-8964. Email? send it to Fred at FarmerFred dor com. Please tell us where you live, because all gardening is local. And it really helps us figure out what the proper solution for your problem might be. Thanks for listening.
Farmer Fred 24:01
Garden Basics comes out every Tuesday and Friday and is brought to you by Smart Pots. It’s available just about anywhere podcasts are handed out. And that includes Apple podcasts, I Heart Radio, Spotify, Stitcher, Overcast, Podcast Addict, CastBox and Google podcasts. And for Northern California gardeners, check out this podcast: the Green Acres Garden Podcast with Farmer Fred, also available wherever you get your podcasts. Thank you for listening, subscribing and leaving comments. We appreciate it.
