I have lots of thoughts about mulch. If that isn’t the most boring introduction to a blog post you’ve ever read, I don’t know what to tell you. But in the horticulture world, particularly in suburban Texas, mulch is huge. Our whole no-dig farming system at the Farmadillo is based on the use of permanent surface mulches to enrich soil life and preserve moisture. So it’s safe to say that at any given moment we’re likely knee deep in mulch of some kind. Mulch has become so ubiquitous that it’s even become a weird Gen Z meme. But there’s a lot of confusion out there about what mulch is and when to use it, which has led to some really horrendous and counterproductive uses for mulch. And in our home garden, we’ve started to even move away from the use of mulch entirely. So if you’ve made it this far in the article without falling asleep I will assume you’re a real mulch freak (or at least mulch curious), so let’s take a deep dive into the meme woodchips, shall we?

Before we get to the Crimes Against Horticulture section, let’s talk about some definitions. At its simplest, a mulch is just anything you put on the surface to cover bare soil. While wood chips spring to mind for most people, there’s a whole universe of other mulches to consider, both organic and inorganic. For organic mulches, the big player is the aforementioned wood chip. These come in all flavors. American gardeners are currently particularly wild about dyed bagged wood chips for some reason, and these fly off the shelves of garden centers. In nice neighborhoods, I would guess that 80-90% of flower beds and borders contain dyed wood chips. Fortunately most of these tend to be dyed a relatively tasteful black (or at least brown), but shopping centers seem to be particularly enamored of the tacky red mulch. Wood chips also come in undyed flavors, including hardwoods and conifers (like shredded ashe juniper). The most economical woodchips by far would come from a place like chipdrop.com, where you can scoop up unwanted woodchips from local arborists or cheap (or free!). In second place for organic mulches would be compost. Most commercial grade, finished compost is used in situations where gardeners want to give a lot of nutrients to plants that need to be fed a lot, principally fruits and vegetables. Compost used as a surface mulch doesn’t need to be tilled into the ground, it can be left on the surface. This is the main principle of any human-scaled no dig farming system. There’s a lot more to say about the types of compost are available and what we prefer, but for the sake of this discussion we can lump it all into one category. Other organic mulches include leaf mould, straw, or mown cover crops (like peas or buckwheat).

The point of organic mulches are threefold. First, organic mulches suppress weeds. When weed seeds can’t touch sunny damp ground, they’ll never germinate. Second, organic mulches help the soil retain moisture by blocking the sun and cooling the soil, essentially putting the dirt in the shade. Finally (and maybe most importantly, depending on your goals), organic mulches biodegrade over time. This is the main way that gardeners build soil fertility over time. Decomposing organic matter is the best way to add nutrients and life to your soil. The mulches that do this best are those that are already higher in nutrients when applied, like leaf mould and compost. Wood chips do degrade over time but much more slowly, and some wood chips (like ashe juniper) degrade extremely slowly and do very little to build soil health compared to compost or standard wood chips.

On the inorganic side, things range from good, to bad, to ugly. To start with the best inorganic mulch, let’s talk about rocks. Yes, rocks are a mulch! And we’re not just talking about soulless shopping center xeriscaping either. Indigenous people in arid northern Mexico have been using rock mulches for millennia to grow agave, which has historically been a staple food in the region. Rocks suppress weeds and retain soil moisture like organic composts, but don’t break down over time (well, not very much anyway) and contibute to the urban head island effect (rock yards typically run 20-30 degrees hotter than vegetated areas in the summer). Rock mulches are applied in much the same way and for the same reasons in the aforementioned soulless shopping center landscaping.

So that’s the good, what about the bad and ugly? Big Ag (in particular Big Organic) is currently addicted to using huge amounts of plastic tarps on their beds for growing everything from pumpkins to strawberries. These inorganic mulches offer many of the benefits of organic mulches but have the advantage of being cheap, easy to apply and permanent (or at least good for a whole season). They are by far the most effective way to keep down weeds and preserve soil moisture, as well as increasing the soil temperature in northern regions where that’s desirable for earlier planting. This reduces (or eliminates) the amount of herbicide being applied, which is why they are so frequently used. But using a disposable mulch has some pretty serious consequences for the environment, namely the problem of what to do with the waste. There are certainly uses for plastic mulches in a well run farm though, particularly when killing off weeds before planting a new bed. But too often we see plastic used as a permanent crutch in no-dig systems. A properly built and managed no dig bed should have no need for plastic after the first year.

And lastly, the ugly. Rubber tire mulch. I won’t say much about this except it’s the epitome of where mulch culture went wrong. It seemed like a good idea, turn a ubiquitous waste product into something useful. Unfortunately tires are super toxic, and rubber mulch leaches toxic chemicals into the ground as they’re exposed to air and water. Oops. Fortunately the only place I’ve ever seen this in the wild is at a tire shop, which is maybe fair enough?

Now for the fun part, Crimes Against Horticulture! Wood chip mulch is a great example of a good concept that’s been completely ruined by people who don’t know what they’re doing (or haven’t read my manifesto). As discussed above, wood chips do a lot of good. But traditional landscapers who have taken this method and run with it have completely lost the plot. The standard use for woodchip mulch now is to use it on top of acres of plastic weed barrier. You’ve seen this style in countless strip centers and soulless apartment complexes across the state. Not only does this create a lot of plastic trash in the ground, but it also inhibits the main benefit of mulch, the soil-building decomposition process. Woodchip mulch is now used in much the same way as vinyl flooring is used in a house, just as a type of outdoor flooring. The galaxy brain use for mulch is now to just use it as a groundcover on its own, no plants necessary! Clean and tidy, no braincells required!

Even without the weed barrier, a mulched garden bed with plants spaced out really isn’t optimal for wildlife. Ideally what you want to create in a bed like that is a small scale living ecosystem. And what do we see in real ecosystem? Plants reproducing themselves and living in close proximity to each other. Plants growing close to one another provide support to each other and cover for animals and insects. Plants also don’t live forever, so a garden without the ability to reproduce itself has a very limited shelf life. This planting method has practical benefit, the more plants reproduce themselves the less plants you have to buy. Plants that support each other need less care from the gardener.

So what’s the best way to use mulch? In my own home garden we use it pretty sparingly these days, pretty much only for paths and directly around newly planted woody trees and shrubs to retain moisture and keep down weeds. Eventually trees and shrubs create their own mulch via leaf litter, so this is just a one time application. If you insist on using mulch, it is still compatible with a “living” landscape if you have a lot of things like Gregg’s Mistflower or goldenrod that spread via rhizome. My general rule however would be to again consider what you see in nature. Where do you see lots of small branches, leaves and other debris? In wooded areas! So try and limit your mulch mania to things that one day could be mulch, like trees and large shrubs. Otherwise, unless you’re trying to give your house the ambiance of a bank parking lot, save yourself the effort and don’t bother with mulch.

The Mulch Manifesto

The Compost Manifesto

The Farmers Market Grift