702 April Mulching

Hey Listener, 

In this month's episode, we’re talking all about that beloved springtime chore, mulching. We play a round of 'Mulch True or False" before discussing the various types of organic and inorganic mulches. We like some more than the others. 

We also have our : 

• Native Plant of the Month: Virginia Bluebells
• Bug of the Month: peach tree borer
•  Monthly Garden Tips: preparing for spring

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 The Garden Thyme Podcast is brought to you by the University of Maryland Extension. Hosts are Mikaela Boley- Principal Agent Associate (Talbot County) for Horticulture; Rachel Rhodes- Senior Agent Associate for Horticulture (Queen Anne's County); and Emily Zobel- Senior Agent Associate for Agriculture (Dorchester County).

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Transcript

Garden Thyme Podcast Transcript

 S7:E02 Mulching (April 2026)

Note: The Garden Thyme Podcast is produced for the ear and is designed to be heard. If you are able, we strongly encourage you to listen to the audio, which includes emotion and emphasis that's not on the page. Transcripts are generated using a combination of speech recognition software and human transcribers, and may contain spelling and grammatical errors.  

:Up beat song:

Rachel

Hello listener, welcome to the University of Maryland Extension Presents: The Garden Thyme Podcast, where we talk about getting down and dirty in your garden. We're your hosts. I'm Rachel.

Mikaela

I'm Mikaela.

Emily

And I'm Emily.

Rachel

In this month's episode, we're talking about mulch.

:Up beat song:

Rachel

You're like, here's spring, let's mulch, you know, let's put down that mulch. And then our flower beds are like nice and pretty.

Mikaela

It's like a spring rite of passage, you know, like it is— it's not spring until there's some mulch on the ground.

Rachel

Yeah, I don't know about you guys, but like It's always a great debate of like the kind of mulch we're going to use because I really like like the chunky bulk mulch versus like the finely shredded colored mulch. I don't want dyed mulch near my property at all, or the— I don't like the finely shredded stuff. I really like that bulky chunky mulch.

Emily

Oh yeah.

Mikaela

And we're going to get into that too.

Rachel

Yes, we will.

Mikaela

There's more of a reason than just Rachel doesn't like it. There's, there's some really good science behind not using it. So mulching is a lot like pruning. It's one of those really common practices that we all pretty much use in the landscape, but it's rarely used correctly. I know that sounds silly to be like, you can mulch a right way, but you can mulch a wrong way. So yeah, exactly. So you'd be surprised how scientific it can be. We're gonna break it down today. We're gonna go into quite the deep dive. Into mulching, what you might want to use, maybe what you shouldn't use, and how to keep your landscape healthy.

Rachel

This is a rabbit hole I can go down.

Emily

Rachel's excited for this. Okay. Before we dive into all scientific things about mulch, we're going to get our brains stimulating a little bit by playing a little game of mulch true or false. Okay.

Rachel

Oh, I love it.

Emily

So I've got 3 true or false questions for you guys and we'll test your mulch knowledge. Ahead of time. So, the first written record of the use of mulch was in 16th century France. Do you think that's true or false?

Mikaela

I'm gonna say true because that just sounds so specific.

Rachel

I'm gonna say false.

Emily

False? Okay, so this is actually me being a little bit of a trick question. So, historically speaking, we have records of mulch going all the way back to 500 BC in ancient Egyptian times, where there are records of farmers using straw as a way to protect their plants from the hot desert. However, the term mulch came from an old French word that, that means soft rotten wood. So it's believed that this is kind of the first time wood and the idea of wood chips being used for mulch is possible. However, we do have a record of other organic materials being used such as stone and pebbles being used in the 1600s, mainly in arid regions. And then in Parisia in the 1800s, there's records of straw being used to keep strawberries protected. So we do have a history of mulch, and there is several scientific publications looking at the history of mulch.

Rachel

That is really cool, Emily.

Mikaela

That's crazy.

Emily

Yeah.

Rachel

Yeah.

Emily

Okay, so here's your second one. So between 2016 and 2020, there have been over 180 fires that started in mulch and spread to buildings.

Rachel

I'm going to say this is true.

Mikaela

Is this in the US or is this like—

Emily

Yeah, this would be in the US. Yeah.

Mikaela

I guess I'm going to say true as well. Again, that seems very specific.

Rachel

I feel like it should be more than 180.

Mikaela

Actually, yeah.

Emily

Yep, so this is true. So this is the statistic that I got from the Massachusetts government. So I assume that the statistic was probably just for Massachusetts, so it's probably much higher across the whole United States.

Mikaela

They talked about the likelihood of fires from particularly dry mulch and cigarette buds and the fact that they can smolder I guess that's not too crazy because if you think about mulch just being dried wood on the ground and you toss a cigarette butt into it or something, that seems like a recipe for disaster.

Emily

Oh yeah.

Mikaela

It's a good reminder to everybody to be careful in the heat of summer.

Emily

Yep. And I imagine some of this might be in front of buildings more so than homes because I think a lot of properties are more inclined to have that mulch put in in the early spring and you're more likely to have someone smoking outside of like a building versus like, yeah, on their own property. And if you do see a smoldering mulch bed, please call 911 so that the fire department can come and make sure that it is truly taken care of because they can smolder for a long period both before and after there are flames. That's it for our mulch true or false.

Mikaela

So let's set the ground rules, no pun intended, because like let's define what mulches are because you people might be surprised. There's a lot of things that we use as mulch and it really depends on the landscape or what you're growing or what your objective is. So the first thing at least I like to do is define what's an organic versus an inorganic, and even what is a living mulch. So organic mulches are using materials that will decompose over time. So they are broken down by microorganisms, whereas inorganic materials are usually made of either mineral or synthetic materials. And when I say synthetic, it's something manufactured like rubber or plastic mulches. So living mulches on the third hand, are ground covers. So these are actually living systems that we use, very low growing usually, and these are kind of an alternative to traditional mulch types. And so the purpose of mulch is not just for appearances, but oftentimes it is used in the landscape to improve the appearance of a landscape, but we apply it around trees, we use them around shrubs or flower beds, usually to define an area where the planting has changed from like a traditional turf area.

Mikaela

But there's a lot of different purposes for mulch. So one of the main things is that it does retain moisture around plant roots. And that's often why we recommend mulching after a new planting, because especially through the summer, new plants are going to need more moisture as, as we get into the dry hot season. And so mulch does a really good job. I should say organic mulches usually do a really good job at absorbing and retaining that moisture around the plant roots. Another thing that mulch is really good at is protecting tree trunks, specifically new trees from damage from mowers or other lawn equipment, especially if you have someone who has a weed trimmer and they go to, um, work around a tree that doesn't have any mulch around it, there's really a good chance that the, the tree bark will be damaged. And as, as we've talked about before, once you damage the bark on a tree, it's really hard for that tree to recover. So it kind of helps reduce that issue. It also prevents mowers from getting too close to the tree, not just for damaging it, but the mower wheels can create soil compaction.

Mikaela

So just like if you drive over the top of a plant's root systems many, many times, it compacts it can actually damage the root system of a tree. So by keeping mowers away from the tree roots, it can reduce that soil compaction and actually help improve the growth of the plant root.

Emily

Mulch is also really useful in suppressing weed growth, and I think this is a reason my dad used to always apply it. We would do the traditional thing where you'd put down newsprint and then we'd pile the mulch on top to make sure that the weeds didn't come up. And is note that if you are using it to suppress weeds, you do want to remove the weeds before you put it down. This is something that can also be put in areas in order to minimize soil erosion. So a lot of times if you see people reseeding a lawn, they'll put down again that straw as sort of like a top cover mulch. Sometimes people will also use bigger areas of mulch on slopes in order to reduce soil erosion. This is where Living mulch really comes in handy with ground covers in hilly areas to help retain soil and prevent erosion. Some of the other benefits that mulch has is it's really beneficial for moderating soil temperature and preventing those extreme temperatures. You're basically creating like a cozy little blanket for your soil in the wintertime and a cool pad during the summertime. Um, your soil does not like extreme temperatures.

Emily

And this helps to insulate it. So over time, it will add some organic matter into your soil as well. And we generally don't recommend tilling or turning your mulch in, but just through the general process of having microbials and bugs and all these other things and the elements out there, your organic mulches will eventually decompose over time. And that allows for some more organic matter to get leached into your soil.

Rachel

We've talked about the purposes of mulch, but now we're going to kind of transition into talking about the types of different mulches that we can purchase, either from our home garden stores that are pre-packaged, or from a landscaping company, just to help you make a better decision when you decide to mulch your landscape. So, we're going to talk about, about 5 different types of mulch that we can use. The first being one of my favorites, which is bark mulch, and this is softwood pine bark, and that's usually readily available. They are slow to decompose, and they have a very pleasant appearance. I love how big and chunky they are, and they usually are about 2 to 3 inches, kind of square oblong-ish pieces of mulch. They are dark colored. It can be purchased in different sizes from shredded to large particle or even nuggets. So, the only downfall about using large pine bark nuggets is that they can float in water, so they may not stay in place if we have a very heavy rainfall, which we do have those on the Mid-Atlantic. And they are sometimes more expensive than shredded hardwood. So those are just a couple caveats.

Rachel

So we also have hardwood bark mulch, and they are readily available and less expensive than other mulches. They decompose relatively slowly, and they're very, very attractive to have on our landscapes. They contain high levels of manganese, which can be toxic to plants and soils, with pHs below 5.0. So, this is another kind of positive to having your soil tested so that you know what your pH is before you put your mulch down. Who would have thought that there would have been an interaction? We also have pine needles. I love pine needles as a mulch. I feel like it gives that added layer of texture and dimension to a home landscape. Pine needles are also called pine straw. They're attractive, they're fragrant, they're convenient and cheap with locations that have a lot of pine trees, and you're going to add a 2 to 3 inch layer around your landscape if you're using pine needles because they have a small surface area. Contrary to popular belief, pine needles do not have the ability to turn your soil acidic. This is a very common misconception. The University of New Hampshire has a great article on this topic that we'll link in the show notes.

Rachel

So you can use pine cones as a mulch, or you can also use gumballs. Oh, I didn't think about gumballs. Those are great deterrents if you have a deer problem or a squirrel problem in your landscape because they're ouchy on their little tiny feet. They don't want to touch them, and they're ouchy in their little tiny mouths. So if you have a precious prized azalea or hosta that you don't want deer or squirrels to munch on, or even rabbits, put some pine cones around them, some gumballs, something else that's a little prickly. They won't mess with it.

Mikaela

Same thing with vole control.

Rachel

Vole control as well. See?

Mikaela

Yeah, because they don't like, um, digging through sharp or jagged things. So, pine cones can be really helpful for that.

Rachel

Yeah. So, if you don't have an abundance of pine cones or gumballs or even pine needles, you can also use leaves. These are nature's mulch right here, right? Especially when shredded, they can decompose very quickly. They improve soil conditions in the process, and you're going to do the same thing with your pine needles. You're going to add that 2 to 3-inch layer. Compost makes an excellent mulch when using a mulching mower. It can, will continue to decompose and it needs to be replaced annual, on an annual basis because of that rapid decomposition. But regular additions of compost will improve your soil structure significantly. And you're only going to add about an inch layer of compost. And I find this a very good thing. Thing for people to do if they have a very new landscape or a new build, because a lot of the areas around your brand new home are— they use fill dirt, and that doesn't have the best soil composition for our new landscape plants. A lot of times there's compaction or just poor soil, and you need that layer of compost to add some nutrients into your soil and some microbes and, you know, all the good stuff that our soil needs and our plants need.

Emily

I actually like the idea for new builds, if you put down that inch of compost and then even come back like a month or so later and put one of the decorative ones over top, if you like the esthetics of that more. I think that compost, especially on a new landscape, like you were saying, Rachel, just to help like rebuild that soil health.

Rachel

Yeah, our current home was built in, I think, 2007, and I'm still dealing with filter issues in some areas, or compaction, or just poor soil. So it takes a long time to amend your soil and get it to be where your plants are going to thrive and grow. So, you know, add some compost.

Emily

It'd be great.

Mikaela

One thing at least I have used in the past, I know many other people have, is fresh wood chips. And usually this can come from like an arborist or a tree company because it's in good supply. It'd be really easy to get it and you can get a lot of it for pretty much free. But one of the troubles of working with fresh wood chips is that they tend to deplete soil nitrogen and can actually cause burn on many plants, especially if you use in abundance. So while this might be a nice option, if you plan to mulch a walkway, or especially like in between raised garden beds or something, fresh wood chips might be a really excellent idea. But if you're using them in the landscape, we usually recommend that people either kind of compost them or let them cure, which means just let them sit sit because they're still too fresh after they've been just chipped, um, and let them sit for at least 6 to 12 months before trying to use it in a landscape around plants. And even then, I might use kind of sparingly. I might use it very tentatively.

Mikaela

Uh, try not to use any diseased material if you can. You might not be able to guarantee that, but, um, if a tree was taken down because of a disease issue and not, you you know, it got knocked over in a storm, you may want to avoid using it altogether. This is not for everybody and it's not for every situation, but if you have the space that allows you to kind of help cure those wood chips, it's a really inexpensive method.

Emily

Wood chips are kind of nice for— is not only for paths, but if you're trying to like kill out an area, like if you're trying to kill down some turf grass to put in like a raised bed, I find that putting down some cardboard or newspaper as a barrier and then putting those wood chips on top is a nice way to let them cure and kill, like shade out that turf grass.

Mikaela

That's a really good point, Emily. And yeah, that is on if you're battling some invasive plants, you're doing some invasive plant control and you're trying to find methods to kind of keep it at bay, using really thick layers of fresh wood chips is a really good method because it'll help kind of burn the plants. It'll exhaust the invasive plant's energy trying to come up through all those wood chips. So yeah, that's a really good point.

Emily

Shout out to Sam Drogi in our bee episode who gave us that idea. That's right, I was thinking of you a minute ago. Yeah, the wood chip drop. I was like, Sam Drogy talked about using this as a way to kill out your turf grass so you could plant more native plants for bees.

Rachel

I know. I registered for chip drop, never got a notification.

Emily

Me neither.

Rachel

I always want to just, you know, chase down the tree company trucks and be like, can I get a drop at my house, please? Do we feel like we feel about boxwood like we do about stones? Because I kind of feel that way. I'm not sure how much I really like stones as a landscaping tool, but everyone has their own belief system, right? And as gardeners, we have to respect that. Some people want to have that ultra-modern esthetic with their house with no landscaping plants, and for those people, bring on the stones.

Emily

Yeah, I think it's also so a little bit of like, uh, where you live climate-wise, because I know like here in Maryland we see it a little bit more in like, again, commercial buildings along like walkways and stuff. But like where my dad lives in New Mexico, it's much more common to have like the lava rock there because it's just really hard to have turf grass. So everyone has like cactus gardens with like boulders and then lava rock around them, which I honestly think in that case looks really pretty.

Rachel

Yes, exactly, in that landscape. But even then, to me, I'm thinking, where are the snakes? Where are the snakes? Where are the scorpions hidden? Because that's like prime snake habitat, right?

Mikaela

Oh my God.

Emily

And see, like, if I'm a snake, I don't want to live in a whole bunch of rocks. I want to live in like some nice bushes someplace.

Rachel

So, we have 3 types of stones that you can use for mulch. We have gravel, just stone, and we have lava rock. And these materials are permanent, so once you put them in place, they're probably going to be there for a while, which makes them great as a foundation or for special plantings where you want to create a rock or alpine garden. Lava rock is usually red in color and weighs much less than gravel or stone, and these materials are often used over plastic or some type of weed fabric. You want to avoid using stone mulches that contain limestone, which can alter the pH, so we don't want to use them around our acid-loving plants since the rocks may add an alkaline element to the mineral in the soil. They can also reflect solar radiation, so it can make that environment and that landscape very hot in the summer. So, if you have foundation shrubs and you have rocks around them, you're going to get some reflection of that heat, and you're going to cause some burning of the leaves or even some heating of the roots of that plant. Rocks have their place, right?

Rachel

Like, if you're doing a dry riverbed, That's absolutely beautiful. If you're doing a rain garden or a bioswale, perfectly acceptable. Right. But like, if you're doing rocks and then you have azalea in the middle, you're going to kill your azalea or your camellia because they're just not going to be happy.

Emily

Yeah.

Rachel

It's—

Mikaela

that's every McDonald's landscape I've ever seen is rock and azaleas.

Rachel

I know. A giant prized rock, you know, like a 2-ton rock. Yes, that you have a place for.

Emily

Rachel's here for the boulders but not for the gravel.

Rachel

Yeah, I'm here for the boulders, but if we're just putting like 2-inch river rock around our houses or on top of our septic systems, don't do that.

Emily

Yeah, at least here in the Mid-Atlantic, I think there are better options. But again, maybe if you're a listener from the Southwest, the rock gardens might be a little bit more appealing to, to you.

Mikaela

I think you're right. I think in areas where xeriscaping or like the dry habitats landscaping, it makes total sense.

Rachel

Yes, it does.

Emily

I love it.

Mikaela

But for Maryland? No. If you're a Mid-Atlantic person, probably not, you know. And that's my biggest gripe. I agree with you, Rachel. I really do not like rocks as mulch, but usually because it's being used in like a parking lot where it's already surrounded by asphalt or other concrete, and then you're mulching these poor plants with even more materials that absorb heat. There's— it's just going to get cooked. There's just no way it's going to survive.

Rachel

I agree. And it makes me so sad too, like, to ride by and see this like struggling azalea that just wants to live, but one, it was planted in full sun and now it's around a bunch of rocks.

Emily

Oh, don't forget it's got azalea scales. They always have azalea scales on them too. Oh yeah, because all that heat.

Rachel

It's just like, come on, pick a different plant. Yeah, or just don't have any plants.

Emily

And I think, or you know what they could do, put some nice ornamental grasses in, right, Michaela? Right, that's great. Some sea oats. You know what, that's perfect. Some nice ornamental grasses, some like, um, the pink fluffy one.

Rachel

Oh, pink mule grass.

Emily

Yeah, I love that. That'll look pretty because it's mainly just in the like ditch areas in between like parking rows kind of there where they're already probably trying to collect like rainwater. So anyways, so there are a few more mulches besides rocks that we don't really recommend using. Um, and the first one is chipped rubber. This, even from an esthetic point of view, kind of just gives playground. Like, do you want your front yard to look like a playground? So this is a mulch that is made of ground rubber tires and artificial plastic pine needles that do not decompose. So these materials are relatively new to the market, and both their effectiveness as mulch and their color retention is still being evaluated. But for right now, we would probably not recommend going with the chipped rubber unless you are kind of in a commercial area where you are doing like a playground and it needs to be like fall safe or something like that. But even then, in your backyard around your own playsets, I'd probably just go with wood chips or the classic sand. Yeah. So I think the other one that we have already vocalized that we don't particularly like is the dyed mulches.

Emily

So you can oftentimes find wood mulches that have been dyed black, red, green. I think those are the typical colors. I almost wish they'd make one that was straight up rainbow because then it would be mildly appealing, but they tend to just go with black or red.

Mikaela

They also have a, like, brown, so it's really hard to tell it apart. Yeah, but it's like a fakey dark brown. It's not like the color of—

Emily

yeah, I think I've seen that one before. Like, it's very obvious, like, that it's, it's slightly like more chocolatey coffee looking than like your typical wood would be. So these do not break down to enrich the soil as much as the undyed mulches do, and there's the potential for them to leach contaminants from the dye, although this is still under investigation and a lot isn't known. About whether or not these dyes are harmful to the environment or not. I also have found that when I've spread this before, it will dye like your gloves or your hands sometimes. So sometimes these mulches are made from recycled wood scraps, which is great for recycling but questionable in terms of contamination from these materials. So in general, all of us probably like the more natural look. If you want a really neat color, I'd go with pine needles over these. But they are out there.

Mikaela

Agreed. I just, I adore pine needles and they're very lightweight. I don't break my back trying to shovel pine needles. It's like lightweight.

Emily

I think the other thing I found with dyed mulches is they look bright at the very beginning, but typically within like 2 months they fade it. And then it's sort of like, they just look fadey versus like some of the more natural stuff fades, but the fade doesn't feel quite as harsh.

Rachel

How much do we hate landscape fabric too?

Mikaela

I was gonna say, um, this is just like a rage fest for how much we hate landscape.

Emily

Maybe we should have done like one we like, one we don't like, one we like, one we don't like.

Rachel

Yes, yes. Or alternatively, tell me how much I hate landscape fabric.

Mikaela

All right, well, let me, let me tell you why we all hate landscape fabric. Although I would say like, yeah, I was going to say, you know, like the landscape fabric or at least landscape plastics, they do have an application for producers, for people who are actually farming, um, for food. And so it's not like we're saying it can't be used anywhere, but in terms of like a home landscape, there's very little application. Maybe if you're doing like a large vegetable garden, then it might be beneficial. But landscape fabrics are a synthetic material that conserves soil moisture and can provide weed control for a short period, is what I would emphasize. And they do allow moisture to permeate through, so it's not like plastics, which the water would sit on top. So they come in two forms: there's woven and spun bonded. So some of the woven types look more like burlap and have the texture of like a a screen, but the spun bonded types have more of a fibrous texture. That's the one I'm more familiar with using in the landscape, or I see all the time, and they tend to look more like fabric, feel more like fabric, and they are generally used on slopes or around trees or just in general in garden beds.

Mikaela

So soil and organic material do collect on top of these landscape fabrics. So, the weed seeds also can germinate in the soil and the debris, and the weed roots can often penetrate the fabric. So, it's very effective for a very short time, but if you're leaving it on there for any length of time, which most people are, it's on there forever, the weeds do just grow on top of the fabric, and it can make it even more difficult to remove, especially if you come back someday and you're trying to plant in that area and you run into the landscape fabric, you either have to cut through it or you have to rip it all out, which is what I am familiar with doing, is having to come back for projects that were done years and years ago and pull that landscape fabric out. So you can remove or cut away any of this landscape fabric near the base of tree roots. I would also say any of those landscape fabrics that are used up tight next to tree trunks or shrubs, they can actually grow into the landscape fabric. They can grow around them, and then you have a real problem.

Mikaela

So woven materials do allow that water and the air circulation through them, but it doesn't provide very good long-term benefits. So they're going to control most weeds, although a lot of grasses will come up through holes in the fabric. Actually, a lot of weeds will just grow up through any hole that they can find. So it needs to be fastened tight so it doesn't get pushed up by weeds, or like if you're, you're using a mower, it can catch on the mower if it's not secured tightly to the, to the soil surface. So adding a couple inches of another mulching material on top would, would help, but I would say just don't use it. Like, that's, that's really my take-home message. I cannot think of a very good application of of using landscape fabric, especially if you plan to apply mulches every year or two. Because what all it does is help bury the landscape fabric, which will never decompose. It will always be there. I don't know if anybody here has good luck with like the landscape paper. Has anybody tried that?

Rachel

I have not used landscape paper.

Emily

I think I've considered using the landscape paper. I think we got a sample sent to the office and I was like, oh, this just looks like newspaper, which is what I typically tend to use, just plain newsprint or brown cardboard below when I put my wood mulch layer down.

Mikaela

I think it would probably act much like using cardboard or newspaper, so it might suppress some weed growth for a little while, but nothing is going to indefinitely control the weeds. Okay, there's always going to have to be some kind maintenance. So don't waste your money, don't waste your time putting down these landscape fabrics. Just use organic mulches that are going to break down and help improve your soil anyways.

Emily

So what I'm hearing is 2 inches of landscape fabric and then 4 inches of rock.

Mikaela

That's right. Actually, what you should do is a layer of landscape fabric mulch and then another layer of landscape.

Emily

Yes, landscape.

Rachel

It's like, it's like a tiramisu of landscape.

Emily

So some of the common questions that we get, or some of the common issues that we come across when it comes to mulching, is how much should be applied and how should you apply it. So typically we recommend with most of the organic mulches that we've talked about today that you're going to want to apply 1 to 3 inches of them in a donut-type shape around trees specifically. So when it comes to your trees, you don't want to do a massive amount right up against the trunk, also known as a mulch volcano. So ideally you want it to be at least 3 to 4 inches away from the trunk itself, but then wide enough to again keep any kind of landscape equipment or provide that protection to the tree. Particularly with newly planted trees, ideally you want to put the mulch out as far as the branches go. You can kind of shrink that in once the tree gets established if you want, and if you want to swap out the mulch for like shrubberies or flowers and stuff like that. But at least for newly planted trees, however far out those branches go is ideally how far you want the mulch to go as well.

Emily

So again, 1 to 3 inches with a gap between it and the trunk. So, big donut shape, no volcanoes, we want donuts.

Rachel

So, we've talked about all the different types of mulches and how they're beneficial to our landscape, but some mulch can actually be toxic, and we call this sour mulch, and it can quickly damage a plant and plant tissue, even lower the soil pH, and cause injury or death to plants. Symptoms that we see include yellowing of the leaf margins, scorching, dropping of leaves, and occasionally the entire plant will die. And although it may be several days before symptoms appear, the spreading of sour mulch can damage plants immediately. So sour or acid mulch is caused by poor handling or storage of the mulch that results in an anaerobic condition. So that's when you have too much bad bacteria and not enough good bacteria. Mulch piles need to be able to breathe to prevent this anaerobic condition from occurring. In the absence of air, microbes in the mulch, usually bacteria, can produce a toxic substance such as methanol, acetic acid, even ammonia gas, or hydrogen sulfide gas, and this will actually make the pile, quote unquote, sour. Sour mulches will smell like vinegar, ammonia, sulfur, even sometimes silage. And we know what a good mulch smells like, right?

Rachel

It's that freshly cut wood or has that earthly smell, that good garden smell. Another way to determine if a mulch is sour is to test the pH. Toxic mulch will have a pH of 1.8 to 2.5. This is a very acidic mulch. To prevent your mulch from turning sour or to cure sour mulch, Mulch piles must be turned once or twice a month, more frequently if the mulch is wet. We're not going to let our mulch pile get larger than 4-foot thick in any dimension if the pile is not being turned regularly. And a good aeration process will eliminate the toxic compounds in 24 hours, but it's safe to let it stay for 3 days.

Mikaela

So, so another issue that a lot of us run into, this is very common, is finding toadstools, mushrooms, and other fungi. So because it's decomposing wood or lignin, you're going to find some of this stuff. Most are harmless, but if you have small children or pets that are notorious for getting into things and, and trying to eat things that they shouldn't, you might want to remove them or, you know, just get rid of them somehow. These fungi are not harmful to landscape plants. There's no known health hazards other than if you eat them. So they can be found anytime during the growing season from April through October, uh, usually following rainy weather, which we get very often. One of the fungi you might run into is a cool one the stinkhorn fungi. They can colonize hardwood bark mulch, so that's something that you'll find very often. And the fruiting bodies, or the mushroom part, comes up in the fall and exude a very unpleasant odor. And they usually do that to attract flies and other kind of pollinators, although they're not really pollinating the fungi, they're just attracting them. So you can scoop up and dispose of these mushrooms as they appear they usually only last like a day or two.

Mikaela

It's really very transient. So consider replacing hardwood bark, which contains a lot of that woody material, with another choice such as pine needles or pine bark. One that we find a lot is the slime molds, and it's just how it sounds. They, they look slimy. They're a fungus-like organism, and it's usually just a nuisance. In mulch. It's usually just an appearance thing that we don't like. They typically appear during warm, damp weather. They'll start up here in the spring, uh, and the resulting masses may be several inches to a foot in diameter. They can vary in color. Sometimes they're bright yellow, salmon colored, or orange. Again, unsightly but very harmless. It just is a mold that feeds on decaying organic matter. That we usually find in hardwood mulch. You don't apply pesticides. Nothing you would apply to the mulch would, would fix it. You simply just scoop it up with a shovel or a pitchfork and remove it. One of the cool ones that we often see is dog vomit mold, which is exactly how it sounds. It looks like a dog threw up. So it's, again, it doesn't look great, but it is kind of cool when you think about it.

Mikaela

I finds them kind of fascinating. Usually after there's a lot of moisture in the air, it looks more, um, viscous is maybe what I would call it, but they do kind of tend to dry out. So you'll find like a hard crust of this slime mold sometimes in your mulched beds, and you can scoop it up and just get rid of it. It's pretty mobile. Artillery fungus is one that causes some people consternation. So this is a microorganism in mulches that can become a nuisance. This shotgun or artillery fungus, it's so named for the fact that it has these cups that hold spores, and they shoot these spores into the air. And so against a white surface such as the side of your house or any other kind of light-colored surface, they stick and, and they resemble little small tar spots, um, on cars or siding and really difficult to remove. It's not like you can just use soap and kind of wash it off. You'd really have to scrub, which you might not want to damage your cars or house. So I would not use mulches that contain cellulose, which is the material in wood.

Mikaela

Because that's where artillery fungus tends to be a problem. So they're— and they're pretty small, very low to the ground. You might not notice them until you start seeing like those flecks of black on the siding. Or if your mulch is already in place, cover the hardwood mulch with pine needles or something where the artillery fungus can kind of be intercepted, where it will be kind of dampened. And actually, Penn State, they have a cool article on what is growing in my landscape, and it talks about mulches with mushrooms, slime molds, and other kind of fungi.

Emily

So that wraps up mulches. So hopefully everyone is ready this spring to go out and mulch properly and effectively, and we're going to avoid those mulch volcanoes. Okay.

: Nature sounds: It’s the Native Plant of the Month with Mikaela. :Nature Sounds: 

Mikaela

Oh my gosh, who knew we could have so much information about mulch? Yeah, I'm a little surprised I haven't chosen it before, but, um, so Native Plants of the Month for April, it's probably almost always going to be some kind of spring ephemeral or spring flowering tree because it's just a wonderful time of the year. Virginia bluebells, Mertensia virginica, these are a great local spring ephemeral. And again, honestly, it's really hard to pick just one Native Plant of the Month, but that being said, we have done an entire episode on spring ephemerals see Season 3, Episode 4. So that would have been April of 2022. We really did a deep dive into those spring ephemerals. So if you want to learn more about them, but I think bluebells just deserve more of the spotlight. And as a reminder, just spring ephemerals are a certain type of perennial plant that emerge and bloom pretty much early in the season before the deciduous tree canopy has had a chance to leaf out. And shade out all of that delicious spring sunlight. And then they start to die back, both the flower and the foliage, when temperatures rise starting in like June.

Mikaela

So when they start to rise in the summer, they sort of die back. So Virginia bluebells, you find them in rich, moist soils of like floodland plains, forests, and woodlands. They will emerge with like broad, lush leaves starting, let's say, March, and then develop bright pink flower buds on plants that reach about 2 feet tall. So the flowers eventually bloom into beautiful, like, bell-shaped flowers that are dominantly bluish-purple, but depending on whether it's a bred variety or even in nature, there's some genetic variation in shades of pink, blue, and purple. The flowers do have a slight fragrance, which might be stronger if had like a larger patch of plants. And that's how they tend to grow is in kind of patches. So luckily bluebells like to self-seed in the right growing conditions. So they will grow in a mat under like a shrub or tree canopy. They pair very well visually with other spring ephemerals, such as golden groundsel or Packera aurea, and even hostas. I know hostas aren't spring ephemerals, but they do, um, look very nice together. And bluebells are dominantly native to the Piedmont and mountain region of Maryland, with several genetic variations that will grow in the coastal plain, although a lot of people argue those aren't like true native ecotypes.

Mikaela

So it does have a broad growing range in the eastern US. So pretty much almost all of the eastern United States, you can find some Virginia bluebells. They are primarily pollinated by bumblebees, and other long-tongued bees, as well as butterflies with really long proboscis to reach the nectaries in this tubular flower. Because it is very long-shaped, the insect would need a longer tongue or device in order to get to those nectaries. All right, so here's my fun fact. You guys know we all love fun facts. Blue flowers are naturally very rare. Only 10% of flower plants worldwide are have blue blooms, and Virginia bluebells are one of them. So the flower buds on this particular plant always start as pink, but as they bloom, they will shift color due to some cellular pH changes that happen in the flower. So it's kind of like hydrangeas, you know, people will apply lime or sulfur in order to change the color of their hydrangeas. A similar thing happens, but naturally, in the Virginia bluebell flowers. And I just think that is really fascinating.

Emily

That is really cool.

: Buzzing: What’s Buzzing, It’s the Bug of the Month with Emily. :Buzzing: 

 Okay, so this month's bug of the month, to go kind of with the mulch theme, is a wood pest that you will oftentimes have issues with if you have those mulch volcanoes. So this month, my bug of the month is the peach tree borer, also known as the peach tree crown borer. Um, so this is a key pest in prunus species in both orchards, nurseries, and then ornamental landscapes. So these would be things like peaches, apricots, cherries, and plums. So both the fruit-bearing species as well as any of the ornamental ones that we might find. So things like flowering cherry trees or cherry laurels, any of those, this insect species will get into. What's unique about this insect species is it is a boring insect. And it is in the order Lepidoptera. So this is a moth that has a caterpillar, and most of the time when we think of boring insects, we think of beetles, but in this case it is actually a boring caterpillar, which is kind of unique. But it's very drab looking for a caterpillar. That larvae is about half an inch and cream-colored near the end of its larvae stages, and what it basically does is it bores into the crown area or the lower part of the trunk very close to the soil line and then chews on the area in the tree right underneath the bark.

Emily

So this, of course, will damage your tree and will stunt it. In addition to its feeding, the wound itself can allow other pathogens and diseases to kind of get in. This should not be confused with the lesser peachtree borer, which is also a similar type of boring moth. However, the lesser peachtree borer tends to go after older trees that are stressed, and it tends to bore into limbs and branches more so into the trunk. So this one really targets the trunk and distinctly, like, right at that soil line. So you can imagine if you had a lot of mulch, you're kind of hiding, and it's providing an area that would make this insect really ideal for it. The injury level a lot of times for this is not very obvious, however, unless you take some time to really inspect at the base of your tree and very much down near that soil level. So what you would likely see is some wet spots in the bark that are going to have like an oozy gummy sap, which comes out as the peach tree borer kind of tunnels into the tree. You may notice some small pieces of wood or frass that are mixed in, that kind of lets you know that you've got this boring insect.

Emily

The adult peach tree borers do kind of resemble wasps. They are what we call a type of clearwing moth, so they are moth-like, but they have very— rather than having scales across their entire wings, they have entire sections where it's clear. So these guys look very wasp-like, and what's kind of unique about this species is that they have sexual dimorphism, so the females and the male will look different. So the females are going to have this blue-black coloration to them with a big orange band, and the males are going to look a little bit more traditionally wasp-like, being black with like yellow bands. It is worth noting that these guys, while they look like wasps, are harmless. They're incapable of stinging. They don't have a stinger of any type. Unlike what we would typically think of as moths being like nighttime flyers, these guys and other and other clearwing borers tend to fly during the daytime. So again, only the immature or larvae stage does any damage to the tree, and they do this by tunneling into that sapwood and then feeding on it. So it takes them about 1 year to complete their life cycle.

Emily

The adult moths will emerge out, they will mate, and then the female will lay her eggs right again at the base of the tree. The larvae will kind of bore in. So the larvae become most active kind of during the springtime when they tend to feed the most and will complete their development in May or June after they pupate. They'll remain in that pupation stage for about 3 weeks and then the adults will come out and fly. The flight period is usually from late June into early September. Into our area, and one female is capable of laying between 200 and 800 eggs. Most eggs are laid in the lower 15 centimeters of those host tree trunks, in bark crevices or under bark flaps, or on the soil near the tree. So imagine again, if you have that massive mulch volcano, you've got lots of cricks and crevices where these moths could lay those eggs. Those eggs would be sheltered from the elements Once those eggs hatch, the young larvae will feed on the tree bark, and then they'll eventually work their way into the cambrium, or that active layer of cell growth between the bark and the wood that gives rise to new sap.

Emily

And they'll feed on that, and they'll kind of grow and live in there all throughout the fall, and then they'll spend the winter in there, and then again continue feeding in the spring, and then pupate, and the whole cycle repeats itself.

Mikaela

Wow, that's dramatic. Yeah.

Emily

Some of the best things that you can do in your own landscape if you've got a tree that could potentially be vulnerable to this would be just to keep those plants healthy. So good sanitation practices, adequate irrigation, good pruning, adequate mulch, but again, we're going to avoid mulch volcanoes and we're going to leave that gap so that we can really inspect the base of our trunks, and we can see issues if they arise. So, and that is my book of the month.

Mikaela

It's a really good reminder why it's challenging to grow organic peaches in Maryland.

Rachel

Yeah, that's the same thing I was thinking. The struggle is real when you are trying to grow fruit in our state, right? I mean, I just don't feel like people really, really understand the difficulty of all the different— not only insect pests, but the diseases and the viruses and just all the things that come into the perfect storm of growing fruit in our state.

: Song: Get you Tips of the Month Here with Rachel.: Song:

Rachel

It's April, it's still a little chilly outside, we can still sow lettuce, spinach, Swiss chard, beets, and any of your other favorite salad vegetables like radishes! And, I already know that you listened to our March episode where we talked all about our love of radishes, so sow some more radishes, people! You want to thin your seedlings of leafy greens to a few inches apart, part and eat the ones you pull, salad toppings. Check your planting charts for final spacing between your mature plants, and this allows your, like, especially if you're doing beets or radishes, to develop that nice bulb that you love so much. Also, plant seeds of carrots, turnips, parsnips in deeply worked and well-drained soil. I have begun to love those seed tapes that already have the carrot seeds already evenly spaced, so that I don't have to thin, and this is really great for tiny hands to use, or our older hands, because carrot seeds are so tiny. So, love some seed tape. Don't jump the gun with your warm season crops yet, okay? We still have a danger of frost in the mid-Atlantic, so So please pay attention to your frost-free dates and follow those.

Rachel

We might get one of those off-ball temperatures where our nighttime temperatures dip below 45 degrees, and that can damage our plants for later fruiting. If you think it's going to frost and you already planted your tomatoes and your peppers, it happens to the best of us. Make sure that you use a floating row cover, cover those little babies, even like a 5-gallon bucket with a floating row cover or some type of quilt over top of it, some straw bales with a floating row cover over top, just to keep them insulated from frost. You can sow some beans or corn outdoors in early May. You can start thinking about it now and prepping that soil, so when your temperatures are above 50 degrees, you can do, you can plant them. You can also pre-start them inside so that they're ready to go out the first week of May, but beans are so easy to start in the ground, and corn is too. Just start them in the ground. You can start your squash, melon, cucumbers indoors to be transplanted in the garden in the next 2 to 3 weeks. So, once again, check your frost date calendar and make sure that we're going to be free of frost before you plant them in the ground.

Rachel

Or, if you want to not have a squash vine borer episode, you could try to plant your squash later than the first week of May. Try for mid-June, wait for that first emergence of the squash vine borer to come out, and then she doesn't have anywhere to lay her eggs into your squash, and she might not attack your plants.

Emily

Are you really going to deprive a hard-working mother squash vine borer from having an adequate place for her children to grow?

Mikaela

Yes, I am.

Rachel

If you didn't start your herb seeds in March, you still have time. You could start basil or tarragon. If you're going to do rosemary or thyme, try cuttings versus starting seeds. The seeds take a very, very long time to germinate, and you might not be successful. So, if you're going to do that, try some cuttings. You could also do cuttings of mint or tarragon. Those are easy, easy, or just borrow some friend's mint, and that's just, mint never dies. So, if you're going to do a cutting, you're going to need some rooting hormone, and you're also going to need some soilless mix as well, and some lights. So, cedar apple rust, disease forms its galls on Virginia cedar, Juniperus virginiana, in April. These odd-looking galls are the first bright orange gelatinous balls with long tendrils and projections. They later turn brown and become hard. They are the alternate host structure for the disease, and it doesn't hurt our junipers. But it can be very destructive to our apple trees, hawthorns, and quince. I love finding them. I think it's just like the cutest little alien gull ever, but they can hurt your apple trees if you have an apple tree present.

Rachel

Continue planting and transplanting trees and shrubs. If you're transplanting a tree or shrub, Make sure that you're choosing quality products. Shade trees should have one single straight trunk. All right, we're not doing the forked trunks because that makes them weaker adults. Planting and transplanting should be completed before the end of June. All right, you might not even be able to get into the ground by the end of June because it might be really hard. So if you're going to do it, make sure you do that in April or May so that your plants have enough time to really develop a root system. Verbenum leaf beetle is a serious pest to our native arrowwood verbenum, cherry, cranberry bush, and other plants. Look for feeding or damage on verbenum and yellow larvae. You can control them because they do defoliate plants, and repeated defoliation can cause death to verbetums. Spotted lanternfly eggs will start to hatch in late April, early May, depending on our weather. And then you're going to start to notice all of our things waking up from hibernation, like our box turtles and snakes, And they're going to visit your yard. Don't be scared of them.

Rachel

If you see a turtle crossing the road, you can stop safely and move it in the direction that it was moving. Don't move it from its habitat. And the same for snakes. I actually cover it, carry a little kid's shovel with me to kind of move them. Scoop them up on the shovel, move it across the road, even for snakes. Many of our spring bulbs have fully emerged and are flowering. Enjoy them while you can and remove the spent flowers, but leave the green leaves alone until it turns yellow and dies back. And I know that everyone has heard the hum of the lawn mowers starting. It's here. The season is upon you. Make sure your blades are sharpened.

Emily

Yeah, gotta mow the lawn, gotta put down your mulch.

Rachel

So that's all the tips on spring things. Yep, all the spring things happening.

Mikaela

All the things Rachel reminds me I should be doing and probably haven't. Probably haven't.

Emily

Yeah, that's okay, there's still time to get started on all of them. 

Well, that's all we have for this episode, listener. We hope you enjoyed it and will tune in next month for more gardening tips. If you have any garden-related questions, please email us at gardenpodcast@gmail.com, or look us up at Facebook, or look us up on Facebook at Garden Time Podcast. That's Garden T-H-Y-M. For more information about University of Minnesota Extension and these topics, please check out UME's Home and Garden Information Center's website at go.umd.edu/extension. HGIC. Thanks for listening and have fun getting down and dirty in your garden. Goodbye!

:Up beat song:

Mikaela 

The Garden Thyme Podcast is a monthly podcast brought to you by the University of Maryland Extension. Mikaela Boley, Principal agent associate for Talbot County. Rachel Rhodes, senior agent associate for Queen Anne County, and Emily Zobel, senior agent associate for Dorchester County.

 
  Emily

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