Lets Talk Mulch

Mulch is one of the most important things you should be doing in your garden. If you aren’t mulching, you need to be, no excuses! Mulch is vital to keeping your soil and your plants healthy. It can keep moisture in the soil, prevent erosion, add nutrients, stimulate healthy micro flora development, discourage weeds, boost harvests, and even gussy up the looks of your beds, depending on which mulch you use. It’s pretty much awesome. But mulch is also complicated, at least, picking it out is, and often that can stop people from choosing a mulch. I’m far from an expert, but I’ve picked up a thing or two in my decades of gardening and months of working towards a degree in horticulture, so maybe I can help you sort it out.

Mulch is, generally, anything that covers your soil. It can be organic or non organic, living or dead, free or purchased. Different mulches do different things, and may or may not be right for you, depending on what you are going for. Do you want something to prevent erosion? Add nutrients to your soil? Keep plants safe during winter? Improve yields? Suppress weeds? Whatever your needs, there’s a mulch for that! So let’s look at some of the options available to us.

Wood chips/shredded wood

This is a very popular mulch for landscape purposes. You can buy it in big bags at pretty much any hardware store or garden center, and you can get it in a variety of different woods, textures, and colors (well, mostly just red, black, and various shades of brown, which I never really understood, if they’re going to dye them, why not offer all the colors of the rainbow? Yellow and teal cedar mulch? Yes please!). You can also often get free wood mulch from local arborists (though you’ll want to watch out for any wood mulch from diseased trees or trees that may have been sprayed with anything). This mulch is popular for use in flower beds, paths, and generally any area you want to look nice. It is somewhat soft to step/fall into (so also a good choice for around play sets), it keeps moisture in the soil, it can help buffer temperature fluctuations in the soil, it doesn’t hurt micro organisms living under it (in fact, it may improve their living conditions), and it is a pretty socially accepted look for adding curb appeal. It can definitely suppress weeds, but you have to lay it on thick to do that well, 3-5″ deep works best for weed suppression. It decomposes slowly, which may or may not be a good thing for your needs, if you’re looking for something that will quickly add organic material to your soil, wood mulch is not the best choice, but if you want something to look nice and work as mulch for a long time, wood is a great choice. One downside is that it can be blown or washed away in certain weather conditions, as well as disturbed by foot traffic, but it’s not a really big issue with most wood mulches, which knit together to form a bit of a mat. And there’s argument as to whether or not the dyed stuff is potentially bad for your plants. I wouldn’t use the dyed stuff around food plants, personally, but I’m okay with it around ornamentals. Some of it can be treated with herbicides though, so watch out! Also, there’s debate as to whether or not adding wood to soil robs it of nitrogen, but it’s not something I worry about, especially not with mulch. Since mulch just sits on the surface, it will only rob nitrogen from the surface of your soil, with no nitrogen in your soil surface, your plants will want to send their roots deeper, improving their strength and resiliency, while making it harder for weed seeds to germinate and take hold in your bed.

Rocks/gravel

Most people don’t think of rocks as a mulch but they totally are when used to cover an area of soil. Of all the benefits a mulch can give, rocks probably give the fewest, but they do a little bit more than just look nice. They help reduce erosion and can suppress weeds some. Of course, it’s hard to clear debris out of them, and things like leaves will break down and become soil in the rocks, soil that weed seeds can germinate in, so they will never suppress weeds entirely. Spoiler alert, no mulch will, but some are better than others if that’s your goal. In my opinion, rocks aren’t great at suppressing weeds. Weeds will grow in the rocks, in the pockets of soil that develop between them, after a while. Those weeds are hard to pull and get rid of, because rock doesn’t give way as well as soil does. And if you ever don’t want it anymore, it SUCKS to dig up, so be a million percent sure you want those rocks there forever before you put them down. Depending on how you obtain the rock, it can be pretty pricey too.

Plastic sheeting

There are two types of plastic sheeting, one I hate, and one I’m going to try this year. The kind I hate is that black stuff you put on the ground, usually under rocks, to try and suppress weeds. This plastic will kill any weed seeds underneath it (it won’t do jack to stop weeds from growing in the soil that accumulates on top of it over time, though). It will also kill everything else underneath it. Who cares if it destroys the soil in an area you don’t want to grow anything in, right? Well, personally, I care about the environment and any dead soil is highly problematic in that context. You’re going to completely destroy the soil structure in that area and it can take decades to centuries to get it back, which means you are kind of screwing anyone who might want to plant in that area in the future. Every inch of soil is an opportunity to sequester carbon, foster biodiversity, reduce the heat island effect, improve water scarcity, and much, much more. Further, having jacked up soil in a part of your yard/land very likely could change how water flows through your property, leading to problems like flooding or the inability to retain water where you need it. Healthy soil holds water at optimal levels much better than soil with terrible structure, so you might be screwing yourself right now too.

The reason people most often want to use plastic sheet mulch is because it suppresses weeds, but, as I discussed above, weeds in rock mulches aren’t generally growing from the soil under the rocks. They’re growing in little bits of composted leaves and debris that end up IN your rocks. And most weed roots are tough enough to grow down through your plastic sheeting as it degrades over time (or gets holes poked in it from traffic on the rocks put above it). So don’t expect plastic sheeting to keep your area weed free for long. What you can expect is that it will eventually crack and tear up into a million gross pieces of trash that will litter your yard. And it’s petroleum based. That just adds insult to energy.

The stuff I’m going to try is colored plastic designed to be placed under plants temporarily to reflect light and confer some benefit. Some offer larger harvests. Others may help reduce pests. I’m going to try some red plastic sheeting under my tomatoes to boost harvest. I have heard from several reliable sources that it worked well for them, so I’m going to give it a go.

Landscape fabric

This stuff is used in the same way as the plastic sheeting I hate, but I hate it a little less. I still don’t like it, but it doesn’t kill quite as much under it, it lets water through, and it lasts longer, so it’s slightly better than the plastic junk. If you want to put down some kind of weed barrier, use this stuff under another mulch. Still, it likely won’t do much to suppress weeds under mulches like rock, for the above stated reasons. Personally, I don’t bother with this stuff, it’s too hard to remove if I want to plant something there eventually. That being said, it does make rock removal a little easier, so if you’re putting down rock, but think it might not be forever, put this stuff underneath.

Dead leaves

Dead leaves are free, organic, break down into your soil more quickly than wood chips, and provide winter habitat for many beneficial insects. Many people consider it the perfect mulch, but dead leaves do have some issues. First of all, in addition to beneficial insects, many pests and diseases also overwinter in dead leaves. The most prevalent of those, and the one that gives me the most grief, is powdery mildew. Dead leaves can also form a dense, wet, mat after a few rains or snows, and that can smother a lot of plants or encourage unhealthy fungal growth (it basically mimics the conditions needed for snowmold to develop, for example). Also, if you live in a community with conservative rules or expectations on how yards should look, your neighbors might not appreciate your choice of dead leaves for mulch. It doesn’t look like a good, conservative mulch choice, and neighbors might be peeved with the possibility or actuality of your leaves blowing into their yard. For all of these reasons, I choose not to mulch with dead leaves. I leave a few piles of them in places where I don’t intend to grow anything, to encourage insects in my yard, and I compost the rest. If you do want to use dead leaves for mulch, it’s a good idea to chop them up first. This discourages them from forming that gross mat that can harm plants, and helps them to break down into soil faster. Also, it’s worth noting here that Michigan State University did some studies that found that if you mow your leaves into the grass in fall, rather than raking them up, it really improves the health of your lawn! There were literally no downsides to this practice. So that’s what’s going to happen to a good chunk of our leaves this year.

Grass clippings

Grass clippings are another mulch choice that is free and readily available. They can also form a mat like leaves, and be considered ugly. Grass clippings contain significantly more nitrogen than leaves do, so they may also reduce your need for fertilizers. However, because of this, some people say using grass clippings can burn your plants, but I have not found that to be a problem myself. If you are concerned about that, but want to use your grass clippings as mulch, you can always turn your grass into a kind of straw. I have done this by spreading my grass clippings out in a thin layer on a hot, sunny, dry surface (I used my driveway) and letting them dry out for a few hours. You might have to go turn it a couple of times if you want to speed up the process. It only took like four hours with no turning for me, but Colorado is a very dry place. It might take longer or not work at all some place more humid (if you have insight on this, let us know in the comments!).

These days, we mulch our grass clippings directly back into the grass as we mow. It’s the best way to restore the nitrogen turf needs right back into it. No, it doesn’t cause thatch to form. Some grasses just form thatch no matter what.

Straw

Straw is kind of a cool mulch because of how it reacts to water. Because of its hollow center, and the principals of cohesion and adhesion, straw tends to suck up water and hold it much like a sponge. It can hold that water an excessively long time, and release it very slowly. It’s a good choice to use around plants that really need their leaves or low hanging fruit kept dry, like zucchini or strawberries. It’s also a great choice for animal bedding, since it sucks up the urine and other moistness that comes out of animals.

Pine needles

Pine needles are often free, and can look a little more nice than dead leaves or straw by conventional standards. They don’t mat as well and they blow away fairly readily. They also take a while to break down. A lot of people are afraid of using pine in any form in their garden because it will put acid in the soil. This might be a legit issue in places with already acidic soil, but here in Colorado the soil is so alkaline that you’d probably have to amend with pine for several hundred years for that to be an issue. If you are unsure, get a soil test before mulching with pine needles.

Newspaper

Newspaper might seem an unlikely mulch source, but it actually works pretty well. It’s one of the better ones for discouraging weed growth, so it’s often used as the bottom layer in a lasagna garden.You can shred it before using between rows in your veggie garden, or you can lay it down flat to cover an area, before piling soil, compost, and other goodies on top of it. Newspaper doesn’t have a lot to offer the soil in the way of nutrients, though, so don’t expect much out of it in that department. There is also some controversy over whether the inks are safe, particularly the colored inks. I don’t have a definitive answer on that, so I try not to use a ton of newspaper. Since I don’t get one delivered, it’s not like I have a bunch of newspapers lying around to use anyhow.

Cardboard

There’s only one way I ever have used cardboard as a mulch, and that’s as a weed barrier under a raised garden bed. You can also use it as the first layer under a lasagna garden, just like newspaper. It probably suppresses weeds better than newspaper, and has less ink on it in general, but if you are using broken down boxes, make sure you remove the tape off of it first, or you’ll be finding strips of plastic in your garden for years to come.

Compost

Compost is kind of like putting more soil down as a mulch. It’s a great addition to your soil, but it’s prone to wash away, and will become part of your soil fairly quickly, so I’m not sure it makes the best mulch all on its own. Generally, I would recommend putting another mulch down on top of your compost, to make sure it doesn’t wash away, but if you are in a bind and don’t have anything else, putting compost on top of your soil is better than leaving it naked. Spread it thick!

Carpet

This is not something you want to leave in your yard, but putting down a layer of old carpet for a few months (maybe all winter?) is a great way to smother out any weeds or turf in order to put in a garden. Carpet can really kill some shit (which is one of the many reasons it kind of grosses me out in my home).

Other synthetic mulches

There are a lot of cool, synthetic mulches out there, made of things like recycled tires and plastic bottles. I often see them used in playgrounds. These are a lot like rocks, they don’t add much in the way of nutrients to your soil, but they keep it covered and probably lend a certain look or feel to your property. I wouldn’t use them in a garden, I don’t know what kind of chemicals they might leech, but I’m not opposed to using them in the right situation. In general, I’m all for recycling things that are hard to recycle.

Living mulch

Living mulch really deserves its own post, but I’ll touch on it here. Living mulch is basically any ground cover plant. Your lawn is a living mulch. When people plant in guilds, the lowest layer of plants is their living mulch. But when most people talk about living mulches, they’re talking about a cover crop, something you grow temporarily, between other crops, to keep the ground covered and maybe fix some nitrogen in the soil. If you till your cover crop into the soil, it’s called a green manure. There are lots of choices for living mulches, what works best depends heavily on your needs and situation.

Many people choose nitrogen fixing plants, like clover, vetch, or beans. These plants pull nitrogen from the air, and convert it into the form of nitrogen that plants need. They then store it and spit some out the roots into the soil. It is my understanding that they only do this when nitrogen is deficient in the soil, which is fine, because if there’s enough nitrogen in the soil already, there’s no reason you should want your plants to add more. But nitrogen becomes deficient pretty quickly in places plants are being grown, especially food plants, so chances are you could use the boost nitrogen fixes will give you.

Other people choose plants that are known as dynamic accumulators. These are plants that usually have long tap roots and theoretically are very good at sucking up trace minerals from deep in the soil, that might be more deficient in the top layers of soil. Comfrey is a popular dynamic accumulator choice amongst permaculturists because you can pick it’s leaves to use as mulch, and it grows back again fairly quickly.

Farmers often choose a cover crop that gives them a second harvest. Winter wheat, rye, and barley are popular choices. Here in the burbs, most living mulches are chosen for aesthetic purposes, a lush lawn, some elfin thyme,  some pretty vinca or snow on the mountain.

Whatever kind of living mulch you choose, they are all great because they keep the ground covered, provide food and habitat for living organisms both above and below the soil, their roots knit the soil together, being the best form of soil erosion, and living plants all sequester some carbon from the atmosphere. Obvioulsy, it’s not possible to use living mulches everywhere, but they are a great choice in many circumstances, so it’s worth considering where you can use them.

I’m sure I probably missed some cool mulch options, what would you add to this list? How do you feel about any of these mulches? Let us know in the comments!

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