Mulch Matchmaking: Choosing the Right Mulch for Your Vegetable Garden - Ep. 302

[00:00:00] So a question that I get all the time is, what's the best mulch for my vegetable garden? In fact, I just had a listener on Spotify comment on one of the episodes because they had been told about the drawbacks to using straw mulch. And my honest answer to this question is, it depends. It depends on what weeds you're fighting. It depends on your climate. It depends on what's available to you and what you can afford.

[00:00:29] It also depends on whether you've got a slug problem, or a vole problem, or a nitrogen problem, or all three. Almost every gardener who asks that question is already doing the right thing just by asking. But the real answer to what's the best mulch is almost anything is better than bare soil.

[00:00:51] Welcome back to Just Grow Something. I'm Karin Velez, specialty crop farmer and garden educator, here to make gardening feel straightforward with grounded in good science information, explained in plain language, and focused on results. Today, we are going to walk through the most common mulch options for vegetable gardens, both organic and inorganic. And I'm going to give you the real picture on each one, what it's genuinely good at, where it falls short, and how to use it correctly.

[00:01:19] So, you can stop guessing and start matching your mulch to your garden. Let's dig in. Alright, mulch. This is a topic that sounds simple on the surface. Put stuff on the ground and plants do better, right? But there's actually a lot going on underneath that layer of straw or wood chips or whatever it is that you use.

[00:01:44] And the choices that you make really do affect how your garden performs across the season. So, before we get into the individual types, let's talk about mulch in vegetable gardens specifically because vegetable gardens have some unique considerations compared to like flower beds or landscape plantings. And I think by the time we run through this, you're going to understand why I am constantly telling you to use mulch.

[00:02:09] I'm sure you guys are sick of me hearing mention or mention mulch in every single episode. But mulch does several jobs at once. And understanding those jobs will help you evaluate every type that we're going to discuss today. Its first job is weed suppression, okay? This is the big one for most gardeners. And let's face it, if we garden, we have to weed. No way around it. But let's try to make it a little bit easier on ourselves.

[00:02:36] Mulch physically blocks light from reaching the soil surface, which prevents weed seeds from germinating. Now, the nuance to this is that it works best on annual weeds, right? So, those are the fast-germinating seeds that need that light to sprout. Perennial weeds that already have established root systems are a totally different story. They're pushing up from below. They're not sprouting from seed.

[00:03:03] And they can punch through most mulch layers without much trouble. And a truly aggressive, invasive weed, mulch alone is rarely going to stop them, okay? So you need to know what you're dealing with before you decide how much to rely on mulch for weed control. Now, I will say, with those perennial weeds, at least having a layer of mulch allows you to see them more clearly as they start to come up.

[00:03:29] And so you can go ahead and get them out of there before they start to become, you know, a takeover situation. Job number two for your mulch would be moisture retention. A good mulch layer dramatically reduces how quickly water evaporates from the soil surface. So a two to four inch layer of organic mulch can actually reduce soil moisture evaporation by 25 to 50 percent. And that is in summer conditions.

[00:03:56] So that means less watering, more consistent soil moisture, and less stress on your plants during dry spells. Job number three is drainage and soil structure. So during a heavy downpour, bare soil is very vulnerable to compaction and to crusting. So raindrops hit with a surprising amount of force.

[00:04:23] And this is enough force to destroy soil structure right there at the surface, which then limits how water moves into the soil. So a mulch layer acts as a buffer. It intercepts that impact. So it slows the water down and it lets it percolate into the soil more gradually. That said, if you have a very heavy or dense mulch layer, it can sometimes redirect water sideways instead of down.

[00:04:52] So this is a case where more is not always better, again, depending on where you live. Mulch's fourth job is soil temperature regulation. So mulch insulates. Okay, so in the warmer months, that means it's keeping the soil cooler, which matters for crops like lettuce and carrots and brassicas that don't love having a hot root zone. In the fall, it holds warmth longer, which is going to naturally extend your season.

[00:05:21] So in the spring, though, thick mulch over cold soil can actually slow down the warming, which is why I tell you to pull it back in the spring and allow that soil to warm up before planting because we're letting that soil warm up faster by pulling the mulch off. And then the fifth and final job for your mulch is soil biology support. And I don't think this gets talked about quite enough. Organic mulches decompose over time.

[00:05:49] So they're feeding the soil microbes and the earthworms, and they're building organic matter, and it's improving soil structure year after year after year. This is one of the things that makes organic mulch genuinely different from the synthetic options. It's not just sitting there blocking weeds. It has other jobs. It is actively improving your soil as it breaks down. So we're going to cover six different organic mulch options.

[00:06:17] Straw, shredded leaves, wood chips, pine needles, grass clippings, and compost. And for each one, I will walk you through its weed suppression abilities, moisture retention, drainage behavior, how to use it, and we'll also cover all the drawbacks. And we're going to start with straw. This is probably the most popular organic mulch for vegetable gardeners. It's one that we have used here for probably the last decade every single year. And there are very good reasons for that. The first one is that weed suppression.

[00:06:46] Straw is excellent against annual weeds when it's applied at the right depth. We're looking at about three to four inches here. It creates a good light barrier and it doesn't compact as quickly as some other materials. And so it maintains that barrier throughout the season. Against perennial weeds like dandelions or like creeping grasses, it's much less effective. Those plants can pretty much push right through.

[00:07:11] And if you have aggressive invasives like Japanese knotweed or the field bindweed that we have out here, you really can't rely on straw alone. You're going to need a little bit more of an aggressive approach. And one important note to make here is to make sure that you're buying straw, not hay, if you can get the straw. And we have used hay in the past. But hay is cut grass or legumes and they still contain seeds.

[00:07:37] Straw is the stem that's left after a grain harvest. And so it should be mostly seed free. And I say mostly because this sort of depends on the source. And so this actually can introduce weed seeds into your garden if there are seeds left from whatever that grain crop was. We haven't had a major issue with that until this year.

[00:08:02] And this year it seems like I'm growing more what I think is oats than a lot of things in our straw. Straw. And I'm actually thankful for a little bit of a change that we have made that we'll talk about here in a second in the next section. But it's definitely causing me to think about, you know, looking for certified weed fee straw, weed free, weed free straw, especially if this is a concern for you.

[00:08:27] Now on the huge basis that we buy straw, like the, you know, 80 to 100 bales that we buy every year, it wouldn't be economically feasible for us to buy nothing but that weed free straw. If you see it in like the landscape stores or if you see it at the garden centers or the big box stores, it's generally called seeding straw. Seeding straw is what I'm thinking of.

[00:08:52] And it's used to help hold like grass seed in place when you're doing landscaping. Okay. That is what you want to look for if you're trying to look for something that doesn't have grain seeds left over that are going to cause you to have to pull those types of grasses essentially, which, you know, or grains out of your garden. So that can be a down, a downside if you're, if you're not careful. But again, it's the main thing that we have used in our gardens and in our fields for about

[00:09:21] the last decade or so. Straw is also very good at retaining moisture. So it's, it's got a very loose, airy structure and that allows the water to pass through really readily if you're watering or just from rainfall. And, and then it slows the evaporation from the soil surface. So if you've got a really hot, dry summer, this is one of its biggest advantages. This is actually how we have managed to not have to irrigate our fields over these years because we have used a very good thick layer of straw mulch.

[00:09:50] So you're going to water less frequently and your soil is going to stay more consistently moist in between those waterings. Straw also handles heavy rain really well because of that loose and airy structure. It doesn't block water from reaching the soil. It just slows it down and it reduces that impact. So it doesn't tend to create that surface runoff the way that, you know, a really solid mulch or compacted mulch will.

[00:10:16] Um, one little bit of a caveat, you know, in heavy downpours, it can sometimes wash away or it can shift, especially if you're gardening on a slope. So if you're on sloped ground, you may need to sort of anchor the edges or use a denser material. So the right way to use straw mulch is to apply three to four inches around your transplants or after your direct seeded crops have come up. Um, an alternative to this is to lay it all out first, completely cover the bed.

[00:10:42] And then you can kind of either make holes where you plan to transplant into or pull it aside to be able to put your seeds directly into the soil. You do want to keep it a couple of inches away from the plant stems. We don't want them to rot where the they're in contact with this straw. Um, sometimes it might need to be refreshed mid, mid season if it starts to decompose or if it thins out a little bit, or if some of it has like blown away, if you have been like really dry, really windy conditions.

[00:11:10] And at the end of the season, you can just work it into your beds. It's going to break down and improve your soil, or you can just leave it in place and just throw your compost over top. Same thing. Now the drawbacks to straw, I think probably the most common complaint is slugs and snails. That nice, loose, moist, airy structure that makes it such good moisture retention in the garden beds, um, is also a fantastic slug habitat.

[00:11:36] So if you already have a slug or snail problem in your garden, then the straw can actually make it worse. So you just have to keep an eye on your plants and be prepared to manage these guys actively. There's all kinds of different things. There's iron phosphate baits, there's copper tape. You can just go out there and hand pick them. You can put beer traps out, whatever works for you in your situation. There's also again that, you know, potential for weed seed contamination. Um, if you can buy really high quality straw or go certified free, sometimes it's just a

[00:12:06] little bit of a gamble. There also is a little bit of a potential for nitrogen tie up. So straw has a high carbon to nitrogen ratio. So as it decomposes, soil microbes consume nitrogen to process all of that carbon. So this can temporarily reduce the nitrogen availability to your plants. It's generally only in like the top one inch of the soil. Okay. In a healthy garden, this is not a huge issue.

[00:12:36] If you're seeing yellowing in some mulch beds, then this might be a factor. So you could compensate by applying a nitrogen source like compost or a balanced fertilizer before you mulch. And I honestly generally recommend that anyway, because we're usually dealing with a nitrogen deficiency. The availability and cost can also sometimes be a drawback with straw. It's, it's widely available in most parts of the country in the fall, right?

[00:13:03] They're generally selling them as decorative straw bales for like, you know, Halloween or the fall, you know, decor type things. But the availability of it and the cost is going to vary a lot by region. And most of us are looking for our straw in the spring, right? So in grain growing areas like here in the Midwest, it can be fairly cheap and pretty easy to find. But if you're in an urban area, it can actually be very pricey and also very inconvenient to get to your house or wherever it is that you're gardening.

[00:13:31] So, you know, a single bale typically covers about 40 to 50 square feet at about the three to four inch depth. So keep that in mind when you're trying to source and think of how many bales you would have to bring to your garden. And then the final consideration in terms of drawbacks for straw is rodents. So straw bales themselves, but then also just having deep straw layers can harbor mice and

[00:13:58] voles, especially as we get into like fall and winter. So if you're in a region with vole pressure, you just kind of have to be thoughtful about how much straw you leave out over the winter and how close it is to like your root crops or any perennial plantings. So overall, straw has been my number one pick for mulch for, like I said, about the last 10 years or so. But again, what works best in my garden does not necessarily work best in yours.

[00:14:34] So your second organic mulch option would be something like shredded leaves or leaf mold. So if you have deciduous trees near your property, you know, trees that actually drop their leaves in the fall, you basically have access to one of the best and probably most underused mulch materials available. So shredded leaves or partially composted leaves, we call that leaf mold. These are genuinely excellent for vegetable gardens.

[00:15:03] Shredded leaves at about a two to three inch depth provide really good suppression of annual weeds. The key word here is shredded. Okay, whole leaves, especially large flat ones like maple or sycamore, they can mat together in a wet, solid layer that gets kind of ucky. It can actually shed water and it can suffocate the plants that are underneath. So run them under a mower or put them through a shredder of some sort first.

[00:15:33] I have actually done this with a weed whacker. Put it into a big barrel and then put the weed whacker in there with the leaves and just let it go to town. Okay. That makes it a much more effective and manageable material. Of course, against perennial weeds, shredded leaves are moderately effective. I mean, nothing's, you know, something's better than nothing, but don't expect them to, you know, stop established thistle or bindweed from coming up. They are excellent for moisture retention.

[00:16:03] Especially, you know, comparable to straw. The material holds moisture well. It doesn't become waterlogged again as long as it's shredded. Leaf mold, right, that partially decomposed leaves with a more sponge-like texture is actually better at holding water than just fresh shredded material, but either one of them is going to get you there eventually.

[00:16:25] And as far as how the material performs under like heavy rain situations, this is where the difference between shredded and whole leaves really matters. Shredded leaves allow the water to pass through reasonably well. Whole matted leaves can create a waterproof layer. Again, it sheds the rainfall rather than letting it reach the soil. So if you're using whole leaves, then you want to make sure that the layer is really thin, right?

[00:16:53] Like maybe two inches. And you want to check after a big rain to make sure that water is getting through. But I really just do recommend, you know, shredding the leaves up before you use them if you can. Again, run them under a mower. Use a leaf shredder. Use a weed whacker. Two to three inches around your plants. We don't want to pile it up against the plant stems. Just like any other mulch, we want to leave that space there. You can add another light layer mid-season as that material starts to decompose.

[00:17:20] At the end of the season, this is a great material to just work into the soil, right? They're going to break down pretty quickly actually over the wintertime. And they are, you know, really good at adding organic matter. Now if you want to make leaf mold, then you can just pile your shredded leaves in a corner of your yard or somewhere near your compost pile or whatever and just keep them moist. In about six months or so, you're going to have this like dark crumbly material that is

[00:17:48] also excellent as a soil amendment. Now the drawbacks to using shredded leaves or leaf mulch. Matting. Okay, matting is the biggest risk. So if you're only getting the leaves partially shredded, they have a tendency to possibly mat down and create those water shedding layers. So try to shred as much as you can before you put them down. There also might be a little bit of a pH effect. Most leaves are slightly acidic.

[00:18:17] And so over time, heavy leaf mulching can kind of nudge your soil pH down just a little bit. This is very rarely a significant problem, especially if you only use them for like one or two seasons. But it's worth knowing about if your soil is already on the acidic side. And if your soil is already on the alkaline side, then this actually can be a good benefit for you. Leaves are free if you have trees or free if your neighbors don't want theirs, which they oftentimes don't.

[00:18:47] In the fall, a lot of municipalities also have leaf collection programs and they might offer free leaf compost. But if you don't have leaves and you don't have a neighborhood source, then you kind of have to find another option here, which isn't always a possibility. Another downside is the labor involved. I mean, shredding leaves takes time and it takes equipment that not everybody has. And so if you're doing large volumes, you might need a dedicated leaf shredder or a

[00:19:15] good bagging lawnmower to make this a lot easier. And then, of course, there is always a possibility of a little bit of nitrogen tie up. Again, like straw, leaves have a high carbon to nitrogen ratio. And so the decomposition process is going to temporarily reduce the soil nitrogen availability. Again, just right there at the surface. So that top inch maybe so you can balance this by adding compost before you throw the leaves down or using a nitrogen rich fertilizer. So next up is wood chips.

[00:19:45] And wood chips have kind of a complicated reputation in vegetable gardens. The concerns are real, but they are often way overstated. And when used correctly, wood chips can be genuinely valuable, especially in permanent beds or pads. And this is actually what we have been utilizing a lot this year. Wood chips are outstanding at suppressing annual weeds.

[00:20:13] A three inch layer up to four inches, right? It's an excellent physical barrier. And because wood chips are denser and heavier than straw, they stay put and they don't blow around. They're also better than straw or leaves at suppressing perennial weeds when you apply them really thickly. So four inches or more can put a real dent in even persistent perennials. Now, invasives, okay.

[00:20:41] We have field bindweed that have come through wood chips. We have johnson grass that has definitely come up through the wood chips. We did manage to really suppress the poison hemlock this year with a good amount of wood chips. And it has to be done properly. So it's going to slow the invasives or the aggressive ones down, but it's not going to stop them.

[00:21:04] Nothing short of persistent removal and covering is going to stop an invasive that has a deep root system. So you can use cardboard or heavy layers of newspaper as an initial layer and then layer the wood chips on top. This is what we have done when creating new raised bed areas or in our landscaping and in between our permanent in-ground beds. And it's working fabulously well. The moisture retention for wood chips is excellent.

[00:21:33] They are among the best materials for this use. The layer stays moist underneath and it dramatically slows evaporation. So in dry climates or during drought periods, this is actually a really significant benefit of wood chips. They also generally handle heavy rain really well. They absorb water. They let it pass through to the soil. Now, the exception to this is very, very fine wood chips or wood chips that have partially decomposed into like a dense layer.

[00:22:00] They can occasionally shed the water if they become compacted. So you just kind of need to fluff the surface after those sort of compaction events and that will help. And if you're gardening on slopes, they stay better than straw, but they're still going to need a little bit of attention. The key distinction with wood chips in vegetable gardens is surface application only. We do not want to incorporate fresh wood chips into our soil.

[00:22:28] This is where the nitrogen tie-up problem becomes serious. Fresh chips on the surface, they decompose very slowly from below and the nitrogen that they consume comes from, you know, the decomposer organisms that are working at the chip soil contact area, right? Not from your plant root zone. This is just the same way as it works with any other mulch.

[00:22:52] So, you know, there is research that they have done on this and they have found properly surface applied wood chips do not cause any kind of meaningful nitrogen deficiency in plants, all right? So, again, just three to four inches on the bed surface, pull the chips back from the plant stems, use them at full depth in your permanent pathways if you want. So, arborist chips, right?

[00:23:17] These are the mixed wood, leaf, and bark material that comes from tree trimming crews. They are often available free of charge, okay? You've got organizations like Chip Drop that can connect you with local arborists who are looking for places to drop loads. The material is going to vary in composition, but it generally works very well.

[00:23:37] Well, we have been fortunate this year to be getting literal dump truck loads from the arborists who are clearing the easements around power lines throughout our entire area this year. And they've just been coming to the farm and dropping it off. So, trust me, we are stockpiling this stuff. Now, of course, there are drawbacks. Again, we have that nitrogen tie-up. This is much more prevalent if you turn this into your soil, okay? The warning is real on that.

[00:24:06] It's just aimed at the wrong use case. If you put fresh chips on the surface, it's not going to suck out any more nitrogen than any of our other organic mulch substances, okay? Just don't till the fresh chips into your soil. They do persist for a while, and this can be a good thing or a bad thing, right? Wood chips break down very slowly, much more slowly than straw or leaves will. So, this is great for pads and permanent beds, but it means they're going to stick around a while.

[00:24:35] Maybe, you know, when you're ready to replant or direct sow, which means you're going to have to pull them back. So, a minor inconvenience, but the fact that they stick around means you have to replenish them less frequently as well. So, that can be seen as an upside. Okay. Just like straw, wood chips can also harbor slugs, can also harbor earwigs, and, you know, to a lesser extent, you might get mice. This is more of an issue in wet climates than in dry ones. We have yet to see any problems with this, but that doesn't mean that it's not possible.

[00:25:05] So, the one drawback I think that is more poignant would be they're not ideal for direct seeding your beds. Like, you have to move the wood chips aside to be able to direct seed, and that takes a lot more effort to pull that heavy layer back than it does, like, the lighter materials, like a straw or leaves.

[00:25:26] So, this is probably the only caveat that I have seen in using these in our beds this year, and so I've tended to apply the wood chips after the plants have already come up, or I am leaving a designated space for where I will direct seed. Now, if you're getting arborist chips, you don't always know what species went through the chipper.

[00:25:49] Okay, most are fine, but black walnut chips can contain juglone, which is allelopathic and harmful to many vegetable crops. But, okay, and this is a big but, I need you to stick with me here really quickly on this because this is another thing that gets thrown around a lot and can cause a lot of undue fear and misunderstanding. Number one, it is rare that black walnut mixed in with a bunch of other wood chips would cause a problem, okay?

[00:26:19] The juglone in walnut is most concentrated in the fruit and the flowers and the buds, right? Then it's also in the leaves and the stems and in the roots, and that contaminates the soil around a living tree, okay? But the amount of juglone, and when it's in its inactive stage, it's called hydro juglone, in the tree itself is very low. It's only located in the phloem and the xylem, which are the water and nutrient carrier channels within the wood, okay?

[00:26:49] And that hydro juglone only becomes juglone when it oxidizes, meaning when it's exposed to air, which is obviously what happens when it's being chipped up in a wood chipper, okay? So again, the vectors for the toxic effect of black walnut on other vegetation are the fruit, the leaves, and the roots. Hydro juglone is colorless. It's generally non-toxic.

[00:27:15] It is immediately converted to juglone by that oxidation, but with continual contact with oxidative conditions, meaning it's exposed to air, and now the plant tissue is drying out, juglone is tied up and decomposed, okay?

[00:27:34] So unless the wood chips that you are using are more than 50% walnut, and they are stacked in an anaerobic situation prior to being used where the air is not getting to them, and you are turning them into the soil or pushing them right up against your crops, your plants should be fine.

[00:27:52] In fact, I will link to a study that showed the overall water-soluble allulla chemicals other than juglone of other tree species like red cedar, red maple, even magnolia, were present in higher concentrations than in black walnut, okay? Black walnut has been turned into this, like, demon plant that it really is not. So if you're truly concerned, then check with whomever you're sourcing your wood chips from

[00:28:19] to determine how much, if any, black walnut is contained within the chips before you take delivery, but don't freak out if they say there's a few here and there and think that it's going to ruin your entire garden because it absolutely will not, okay? All right, let me step down off my soapbox now, and let's continue. Pine needles, all right, or pine straw. They often call it pine straw in the south. These are another really excellent mulch option that is especially useful in regions where they are readily available.

[00:28:49] They don't get as much attention as straw or wood chips, but they definitely have some really useful properties. Pine needles interlock and they form a mat, and so that is going to suppress those annual weeds reasonably well if you're using them at about a two to three inch depth. They're not quite as suppressive as wood chips or a really densely applied straw, but they are effective for season-long weed management in beds.

[00:29:16] And, of course, like other organic mulches, they're not going to stop perennial or invasive weeds that are pushing up from below. You need more than just the pine straw, okay? The moisture retention for pine needles is good, not as outstanding as straw or wood chips, right? Pine needles are lighter. They're more porous, and so they allow rain to readily, you know, get through, and they will reduce evaporation, but their water holding capacity is lower.

[00:29:46] So if you are in a very hot, very dry, you know, climate or you're experiencing those types of conditions, you might need to go slightly thicker with your application if you are using pine needles. They actually handle heavy rain pretty well. The interlocking structure resists that sort of washing away or that movement actually better than straw does, and, you know, they do still allow the water to pass through without getting compacted. So this is actually, you know, makes them a pretty useful choice if you are gardening on slopes

[00:30:14] or if you are gardening in a very high rainfall area. The general rule on pine mulch or pine straw is two to three inches, okay, around your plants. They stay in place pretty well. They don't need much maintenance through the season, and they break down fairly slowly. So you'll get a couple of seasons out of just one application if you manage it properly.

[00:30:37] Now, the most common worry about pine needles is the pH, okay, and it's partially warranted. Pine needles are mildly acidic, and so after over several seasons of using them, they can gradually lower the soil pH. You know, most vegetable crops prefer something that's close to neutral, so that might become a problem over time, but just take a soil test, okay? Annual soil tests, best way to stay ahead of it, okay?

[00:31:07] A single season's application is very unlikely to cause issues, but if you have consistent long-term use of them, then just take a soil test every season to see where your pH stands and see if you need to add some lime or something to bring that pH back down. Or back up, I'm sorry. If you have pines, obviously you have free mulch. If you don't, you can buy bagged pine straw at garden centers in some regions, okay?

[00:31:33] I don't know that I could walk into my garden center here and find bagged pine straw, and if I did, it would probably be pretty expensive, especially for the amount that I would need to buy. But in the southeast U.S., this is pretty widely available in some other regions, maybe not so much, so that can be a drawback. Um, you know, and then I guess you could see this also as a drawback, just like the wood chips, they break down pretty slowly. So it means they're not going to contribute as quickly to, like, your soil organic matter

[00:32:02] as something that decomposes more quickly, like leaves or straw. But if you're looking for longevity, then the pine needles are pretty much on par with something like your wood chips. I will say, though, that pine needles or pine straw, pine mulch, whatever you're going to call it, is not ideal for pathways, okay? They can become very slippery when they're wet, and that makes them a very poor choice for walkways. But they're fine for your bed surfaces,

[00:32:29] so maybe use the pine straw in the beds and then use wood chips in your walkways. Next up is grass clippings, and I think they're kind of misunderstood as a mulch. Um, if you use them wrong, then yeah, they're a matted, slimy mess. But if you use them correctly, they are a high-value, nitrogen-rich,

[00:32:55] also free resource that most gardeners are already tossing in their compost pile. So for weed suppression, when you use grass clippings correctly, um, they're pretty good at suppressing annual weeds. Um, they have a very fine texture, and so that can create a dense layer that is going to block the light. The problem is, if it's applied too thickly, then they mat together into a solid, water-shedding, anaerobic layer that starts to stink,

[00:33:24] and it doesn't work as well as a mulch. So the key with using grass clippings is thin layers. So like one inch or less, and then let it dry, and then add some more, and then let it dry. That works much better than trying to do like one thick application. So if you're doing it this way, you know, the thin layers, that's going to retain moisture without becoming anaerobic. So as they dry, they kind of form this loose mat,

[00:33:53] and it does a reasonable job of slowing down the evaporation, so that's going to trap the soil moisture better. If we're working with those thin, dry layers, they also handle rain reasonably well. It's those thick, fresh layers that can compact really quickly, and that's going to have that water-shedding effect. It's going to direct water away from the soil. So if we're applying it in thin layers, and we're letting each layer dry before we're adding more, then that is going to, you know, keep them in place in terms of rainfall,

[00:34:21] but also let the rainfall come through. So truly, I mean, the key technique is thin layers, no more than an inch or so at a time, less than an inch, let them dry out, add another layer. You can build up a two to three inch layer like this in total over time. Just like any other organic mulch, you want to keep it away from the plant stems, right? Especially if you're in a really humid climate, because they can, you know, contribute to rot.

[00:34:50] They are high in nitrogen. So as they decompose, they're going to release that nitrogen into the soil. So that is a genuine benefit, especially if you are using it as mulch around heavy feeding crops. Now, the real and serious concern if you are using grass clippings that you're not sure of the source of is herbicide contamination, okay? So grass clippings from lawns that have been treated with certain broadleaf herbicides

[00:35:21] can carry that residue. And that can persist through that decomp and that can damage or kill our vegetable plants. So you start getting those twisted, cupped or stunted plant growth that we talked about in episode 300 when looking at like tomato problems. If you are not 100% sure whether the lawn has been treated, don't use the clippings, okay? This applies to clippings from your own lawn if you use herbicides or from a neighbor's lawn or from your municipalities, okay?

[00:35:50] When in doubt, leave it out. We don't want that kind of contamination. That is like a gardener's worst nightmare. The other potential problem would be like weed seeds. If your lawn has gone to seed, those clippings are gonna carry the seeds to that. So let the lawn grow past the seeding stage before mowing it if you're gonna collect it for mulch or hot compost the clippings first to kill the seeds. And, you know, hey, this is great. These are free if you have a lawn, but not everyone does. And so, you know, the volume too

[00:36:20] from a typical home lawn is often limited. So you may not have enough for your garden. You might have to get them from your neighbors or this just may not be something that's available to you. They do decompose fairly quickly though too. You know, they break down fast. So that means they're not gonna last all season. You're gonna have to plan to replenish them probably multiple times. And then finally, compost, right? Compost isn't always thought of it as a mulch, but it absolutely can function as one. It actually was the mulch that we used to use most often

[00:36:49] prior to making the switch over to using straw. And part of this is because it comes with really good soil building benefits that none of the other options can match. But the honest truth about using compost as a mulch is that it's not as good at weed suppression as the other mulch types. In fact, it probably encourages some. I mean, it's dark, it's finely textured. It's actually a pretty good germination medium,

[00:37:19] you know, both for our plants, but also for weed seeds. So a thin compost layer by itself is not gonna suppress many annual weeds. It's not gonna touch perennials. But where it kind of shines as a mulch is in combination with other materials. So we used to use it as a straight mulch because we applied a good two to three inches of it. What we've switched to doing is applying like an inch of compost as a base layer

[00:37:47] and then topping it with like two inches of straw. Or now in this case, we're topping it with wood chips. So you get the soil building benefit of the compost plus the weed suppression of the top layer. Okay, this is gonna help with moisture retention quite a bit. Compost is highly moisture retentive and then a layer on that soil surface is going to significantly reduce the evaporation while it's also feeding the soil biology below. It handles rain really well on its own, right?

[00:38:16] But it can form a slight surface crust after a heavy rain because it is that finely textured material. This is usually minor. It doesn't really cause significant problems. The bigger issue is that the rain can wash the exposed compost away. So once again, using it as a base under another mulch layer is genuinely the best approach. So like I said, one to two inches as a top dressing or a base layer under your other mulches, straight compost application.

[00:38:45] It'll work well in like cool wet climates where you want the soil building benefit, but you don't need aggressive weed suppression. But if you're in a warmer or a dry climate, then you're gonna wanna pair it with something else as a top layer. The biggest drawback other than the poor weed suppression is probably cost. Like if you're having to buy compost, a good quality finished compost is one of the more expensive mulch options if you're buying it. If you're making your own, okay,

[00:39:14] the material's essentially free, but it requires time and management. But if it's not well managed, then the other drawback too is going to be, if it's not fully finished, it can introduce weed seeds. So make sure that you are buying from reputable sources or make your own compost and make sure that it has reached and held temperature long enough to kill those seeds.

[00:39:43] Okay, and then we're gonna take a real quick look at inorganic mulches. Primarily landscape fabric or weed cloth, depending on what you call it, and black plastic mulch. They're widely used. They're worth understanding, even if they're not the sole focus of today's episode. Landscape fabric or, you know, weed cloth is really good at suppressing annual weeds. Okay, it blocks the light very effectively.

[00:40:11] It suppresses annual weeds really well. It is very durable. Okay, it's not gonna decompose. You can use, you know, one piece over and over again. Through several seasons. It does, if you're using a better quality, like woven fabric, it does allow water and air through while suppressing the weeds. And that's also going to reduce the soil moisture evaporation reasonably well.

[00:40:40] The problem with landscape fabric is, I mean, it has a reputation problem, and I think that reputation is pretty well earned. Um, there has been a ton of research and just real world experience that points to a lot of these issues. Um, the perennial and invasive weeds being one of them. Um, and again, I'm talking from both a research perspective and also from a personal experience perspective.

[00:41:09] Landscape fabric is initially really good at suppressing annual weeds. But perennial weeds with established root systems will punch right through it. And some invasive grasses will actually grow right along the top of it. So, you know, over time, weed seeds are gonna germinate on top of it as well in this just sort of thin layer of debris that accumulates on top of the fabric,

[00:41:36] what makes it progressively less and less effective as time goes on. The other problem with landscape fabrics is that it will significantly reduce gas exchange between the soil and the atmosphere, and it limits the movement of soil organisms. Um, so we're, we're disrupting the soil biology here, the organic matter. Um, it's also, you know, limiting the movement of water as well. So over multiple seasons, it can degrade the soil ecosystem beneath it.

[00:42:06] And what goes down eventually has to come back up, right? Landscape fabric that has been in place for several years is bound to, like, plant roots and soil structure. And so pulling it up is genuinely just miserable work. And the other part of this, too, is that these are all plastic-based fabrics. And so, of course, when you expose those to the sunlight, they are going to break down into small plastic fragments over time.

[00:42:33] Okay, so this is a real soil contamination issue. So the bottom line with landscape fabric is it's most useful in permanent situations where you're not regularly replanting, like under a gravel pathway or around established trees. But it is much, much less useful in vegetable gardens where we're turning over beds pretty regularly and we need our soil to stay healthy. If you use it,

[00:43:03] I would absolutely recommend that you commit to removing it. Like, at the end of every season. So the soil can breathe and you can add organic matter. We have successfully used landscape fabric in our larger fields with the addition of a light layer of straw mulch on top. So it helped keep that plastic cooler and it helped prevent the annual weeds from dropping on top and germinating. But again, it needed to be pulled up at the end of the season to keep its effectiveness

[00:43:30] and not turn into a detriment to the soil beneath. And honestly, at the end of the season, that was the last thing I wanted to be doing. So we stopped using it. Although I am looking at using it again, probably next season because of the perennial weed pressure that we're facing in one of our fields. And then the other alternative to this landscape fabric would be black plastic mulch. It's different from landscape fabric because it's specifically designed as a seasonal temporary tool.

[00:44:00] And within that context, it actually performs pretty well. It does an outstanding job at the annual weed suppression. I mean, it blocks 100% of the light. So it's going to suppress virtually all of the annual weeds. It warms the soil. So I mean, it's black plastic. It's going to absorb that solar radiation. So it's going to warm the soil underneath significantly faster in the spring, right? So if you've got, you know, heat loving plants like tomatoes and peppers and melons and sweet potatoes,

[00:44:28] it's especially helpful for those. And the moisture retention is excellent, okay? It's going to prevent all evaporation from the covered area, which also comes with a set of problems. The key drawback to this black plastic is the fact that it is solid plastic. And so it's going to prevent the rain from reaching the soil with the exception of the little holes where your individual plants are. So you need drip irrigation underneath or you need to hand water around the edges. Without it, the plants under the plastic

[00:44:58] are going to totally dry out even if you're having heavy rains. The other consideration too is overheating. I mean, in midsummer, in warm climates, that black plastic can make the soil way too hot for the plant roots. So there is like silver or red plastic that you can use for the summertime or do like what we did with the landscape fabric, which would be to plant, you know, plant place organic mulch on top of the plastic.

[00:45:25] Um, black plastic does not do your soil any health or any help, any good whatsoever, right? There's nothing for the soil biology. It's purely functional. And then you have the disposal of it, right? Plastic mulch is single use. So it's going to go straight to a landfill. They do have biodegradable plastic options and they're getting better, but they're definitely more expensive. Their performance kind of varies. I have seen these just end up completely shredded

[00:45:54] in somebody's field by the end of a season. So I think the bottom line on the black plastic is it's a legitimate tool for specific situations, right? Warming the soil up for like really heat loving crops, maybe maximizing weed suppression if you have a really high pressure season, um, extending the season on both ends. Um, you definitely have to use it as a seasonal tool with irrigation in place. And then you might reap these benefits,

[00:46:23] but is probably my least favorite option out of all of the options. So how do you choose which mulch should be used in your garden? Um, I think, you know, you just have to kind of think through your garden situation. If you have really heavy annual weed pressure, then you might lean towards straw or wood chips or using a season of black plastic mulch. You know, make sure that you, if you're using the organic versions,

[00:46:53] putting them at the proper depth, don't shortchange yourself on how thick you put this down. If you have perennial weed pressure, I'm sorry to say, no mulch alone is going to solve this, okay? You have to start with removal, whether that's solarization or cultivation or manual removal, whatever it is. And then you have to suppress the regrowth. So putting down, you know, some sort of a barrier like cardboard or, you know, heavy layers of newspaper

[00:47:22] and then putting down like wood chips at about a four inch depth, that is going to give you the best odds of slowing perennials down. The root systems just absolutely have to be dealt with. If you're in a hot, dry climate, moisture retention is likely your priority. So straw, wood chips, compost, these all perform really well. Black plastic mulch would also work with irrigation in place, but that might give you some concern in terms of how hot that soil is going to get

[00:47:52] in the middle of your summer. So you might need to also use some organic mulch on top of that plastic. If you're in the opposite, if you're in a cool, wet climate, then maybe drainage and soil warming matter more to you. So thinner layers of straw or shredded leaves are going to work well for you. You don't want those heavy applications that might hold the excess moisture or harbor those slugs. And you likely need to pull mulch back from the beds in the early spring to let the soil warm up faster.

[00:48:22] If cost and availability are your main constraints, then shredded leaves in the fall, grass clippings in the summer, any free arborist trips that you can get your hands on, these are going to be your best friends. These can all be sourced for free or for nearly free in most areas. And then if you want long-term soil improvement, compost as a base layer under straw or wood chips, this is going to give you the best of both worlds. Weed suppression on top, soil building below. This is the approach

[00:48:52] that I come back to again and again. And if you want just the simplest system possible, straw or wood chips at three to four inches. Put it down once at the start of the season, refresh it as needed. That's it. You don't have to overthink this, okay? Remember, the principle that ties all of this together, any mulch is better than bare soil, okay? If all you have is cardboard boxes from a delivery, lay those down, okay? If you have a bag of hay from your kid's school project,

[00:49:20] all right, use it if that's all you've got, right? The specific material matters, but just the act of covering the soil, any covering, starts doing good things immediately. All right, my gardening friends, that's it for today. In the show notes, I'm going to include links to the resources that I referenced on mulch selection, application depths, weed suppression, and the soil biology. And of course, the black walnut deep dive if you really want to nerd out.

[00:49:49] I will also link to a Chip Drop resource so you can look into getting free arborist trips in your area. The main takeaway is don't let the perfect be the enemy of the good out there, okay? Cover your soil. Match your mulch to your conditions when you can. And just keep experimenting. Every garden is a little different. And what works brilliantly for me or for your neighbor or for that expert in the Facebook gardening group, it might need some tweaking

[00:50:19] for your garden. And that's how you find the perfect mulch. Until next time, my gardening friends. Keep on cultivating that dream garden and we'll talk again soon.