If you’re a gardener, you’re probably somewhat familiar with the concept of mulch. It’s a gardening essential yet many people don’t give too much thought about it—it’s just a ground cover, after all.
But is it just a ground cover? And why does it matter?
Today I’m going to break down all things much (no pun intended) and talk about where, when, and how you can use this important material in your garden. I’m also going to share my 12 favorite organic landscape mulches to consider for your vegetable garden or flower beds (including mulches that you might not have known were even an option).
Let’s dig in!
- First, what is mulch?
- Organic vs. inorganic mulch
- Where can you use mulch?
- When should you apply mulch?
- How do you apply mulch?
- Best types of organic mulch
First, what is mulch?
In horticulture, mulch refers to any type of material spread as an extra cover layer on top of the soil. The thickness of the layer can vary, but it’s usually at least an inch or two.
Mulch is pretty useful in gardening, and it has many different benefits:
- To make it harder for weeds to grow: Seedlings are smothered by the mulch layer and without light, some seeds won’t germinate at all.
- To keep moisture in: Mulch helps prevent evaporation, so you won’t have to water as often.
- To retain warmth and regulate soil temperature: Mulch offers insulation from cold and heat, protects plant roots from the damaging effects of extreme weather, and prevents frost heaving (where the soil expands and contracts from the continual freezing and thawing of water in the earth).
- To protect the soil structure: A layer of mulch can help reduce runoff during rainstorms, prevent soil erosion, and keep the soil from forming a hard pan (crust) in hot, dry weather.
- As a slow-release fertilizer: Many organic mulches release nutrients into the soil as they decompose.
- For decorative purposes: Mulches can be used to tidy up a bed and create a more cohesive look throughout the garden.
Mulch generally falls under two categories: organic and inorganic.
Organic vs. inorganic mulch
If you’re thinking about using mulch in some parts of your yard, the first step is to decide whether the space is best suited for an organic or inorganic mulch (biodegradable vs. non-biodegradable). Both have their pros and cons.
Organic mulch is made from natural materials, usually shredded into small particles. One of the key characteristics of organic mulch is that it offers all the benefits of mulch mentioned above, including enrichment of the soil as it breaks down.
Organic mulch has to be reapplied regularly, although the exact time it takes to be processed into the soil by bacteria and fungi varies. Some (like cocoa hulls) break down much slower than others (like grass clippings).
Caution: Organic mulches sometimes come with surprises—like weed seeds, mushroom spores, or, unfortunately, pesticides and other toxins. Be sure to source your organic mulch from a reputable supplier to avoid introducing weeds and other unwanted elements into your garden.
Inorganic mulch refers to any mulch that consists of manmade materials. I’m sure you’ve seen those little rubber bits covering playground floors before—that’s a type of inorganic mulch called rubber mulch.
Other examples include plastic mulch (the plastic sheeting that’s often used on commercial farm crops) and landscape fabric. And although they are technically natural materials, pea gravel, crushed stone, and seashells are also considered inorganic mulches because they don’t break down.
Did you know? Ground cover plants, like thyme, clovers, ice plants (a type of creeping succulent), moneywort, and even moss are also sometimes considered a type of mulch. These types of “living mulches” can be left to grow around other garden plants permanently and offer many similar benefits, like moisture retention and weed suppression.
Where can you use mulch?
One of the most popular uses of mulch is in flower and vegetable beds. It offers many advantages: smothering weeds, keeping moisture in the soil, and preventing soil-born diseases (which happen when infected soil is splashed onto the leaves of plants).
Organic mulch is preferable for garden beds in most cases. Going for something that breaks down relatively quickly (such as straw or leaf litter) helps feed microbes in the soil and improve soil fertility.
Trees and shrubs
Unless they’re still young, trees and shrubs aren’t usually at risk of being overgrown by weeds. Still, mulch is beneficial because it helps regulate soil temperature (especially in harsh winter climates) and improves soil structure (by reducing the impacts of soil erosion and compaction, which can harm root systems).
Organic mulch is usually preferred for trees and shrubs, though most gardeners prefer to go for a type that doesn’t decompose too quickly. Wood chips is a good choice to use here.
If you’re going to mulch around a (young) tree, make sure not to overdo it. An inch or two is enough!
Don’t create a “volcano” around the trunk where boatloads of mulch are piled up right against the bark, as this can cause bark decay as well as rob the roots of oxygen, leading to tree stress.
Paths and walkways
Using mulch on garden paths helps keep them free of weeds and prevents them from turning into a slippery, muddy mess if it rains. But nobody wants to wheelbarrow in several yards of mulch a few times a year to replenish their walkways, right?
Because of this, inorganic mulch is often used for paths and trails. Some folks go for wood chips since they’re fairly economical (or even free, if you’re able to source wood chips from an arborist who needs to unload them), but they don’t last forever.
So for a low-maintenance option, pea gravel or crushed shells are probably your best bet.
When should you apply mulch?
If you’re starting seeds, you can apply a very thin layer of mulch (no more than half an inch) to help keep the soil surface consistently moist. Once your seedlings reach 4 to 6 inches tall, add another inch or two of mulch on top.
Most organic mulches will last through an entire growing season and should only need to be reapplied in spring and fall. If you see that yours is starting to get a bit sparse (or has blown away), make sure to replenish it so that your soil is always covered with 2 to 3 inches of mulch. (More than that is unnecessary and in some cases, may even be detrimental to plants.)
In fall (before the first frost), apply a heavy layer of mulch to protect the soil from frost heaving, protect the crowns and root systems of perennial plants, and prevent a crust from forming on the soil surface.
The exact amount will depend on your climate; milder regions may not need more than 2 to 3 inches to take them through winter, but colder regions can use as much as 8 inches (particularly over any overwintering plants, such as fall-planted garlic or perennial herbs, perennial vegetables, and shrubs).
Even if your garden is empty, you should still throw on some mulch—never leave the soil bare, if you can help it. That’s because soil nutrients can be depleted by heavy rains, and mulch works to reduce leaching and surface water runoff, keeping the soil structure intact.
Is too much mulch a bad thing?
Yes, I know I just said three paragraphs ago that too much mulch can be detrimental, but that’s only true of actively growing plants, which need access to oxygen and water.
In fall and winter when perennials go dormant, their root systems need to be protected from desiccating winds and freezing weather. Mulch helps hold in moisture (so plants stay hydrated despite cold drying winds) and keep the soil from uprooting plants during repeated freezes and thaws.
Once the weather begins to warm up in early to mid-spring (depending on where you live), you can start to remove some of the mulch and thin out the layer to increase airflow to the roots.
How do you apply mulch?
Start by figuring out how much mulch you’ll need for your space. You can use a mulch calculator like this one to figure out how many bags, cubic feet, or cubic yards to buy from your local garden center or landscape supplier. (It even lets you calculate mulch for different shapes of garden beds, like triangles or trapezoids!)
Once you have the mulch onsite, here are a few simple guidelines:
- Remove any weeds in the area first. (They can be tenacious and will find their way through the mulch!)
- Spread a 2- to 3-inch layer of mulch on the ground around your plants.
- Leave some breathing room—mulch should always be kept a few inches away from stems and trunks.
- To prevent matting, especially with denser mulches like leaf litter, periodically fluff up the mulch (with a small rake or your hands) throughout the season.
Best types of organic mulch
Got a compost pile? Awesome, you’ve got mulch!
I know compost is usually used as a soil amendment, but if you have some left over, think about it: it’s free, it has loads of nutrients, and it’s full of beneficial microorganisms, worms, and other natural decomposers. You can use compost as is; no need to add another mulch layer over it.
If you have a large area to cover, buying compost in bulk is a great way to feed and protect the soil at the same time.
When I planted my fruit orchard a few years ago (seen in the image above), I spread several inches of forest-based mulch around my trees to “tuck them in bed” for fall and winter. The steaming compost kept the young root systems warm and enriched the soil as it worked its way down.
If you’ve got trees in your yard, don’t discard the leaves after you rake them up in fall.
Chop them up (with a string trimmer) or shred them into little pieces (with a lawn mower) and scatter them over the soil. If your leaves are on the small side (like those from aspen trees), you can even leave them whole.
Smaller bits of leaves break down faster and are less likely to mat than larger whole leaves (such as those from maples or oaks). To aerate large leaves, you can mix them with pine needles or grass clippings so they don’t clump together (making a “salad mix” like this also benefits the soil by providing different types of nutrients).
A by-product of mushroom farming that’s sold to the public in some places, mushroom compost makes for great mulch. It’s high in calcium and other nutrients, improves water retention, and attracts earthworms.
Sometimes known as spent mushroom compost (referring to its use as a media for mushroom growing), it usually contains a good amount of chalk (up to 30 percent) because the “bed” that the mushrooms were grown on is encased in chalk. This could make certain kinds of mushroom compost more on the alkaline side of things, though it generally has a neutral pH that’s suitable for most plants.
The downside? Mushroom compost may have high levels of salt, so I recommend using it in a garden bed where any excess salt will be diluted by the existing soil. (Try to avoid using mushroom compost for potted plants.)
Straw is a very popular mulch option, as is (to a lesser degree) hay. Yes, there is such a thing as (mostly) weed-free hay, like 100 percent alfalfa or timothy.
Straw and hay are commonly used as a winter mulch, but are good choices for your vegetable garden in summer as well. These materials are relatively cheap, readily available, lightweight, and easy to apply—even my kids love to help me mulch with them.
When sourcing straw or hay to use in your garden, be sure to ask the supplier if it’s unsprayed. Pesticide residues in treated grasses can wreak havoc on the soil by stunting the growth of your plants.
Also known as bark chips, shredded bark usually comes from the chopped-up outer bark of conifers like fir, pine, and redwood. Because different tree species have different exteriors, shredded bark can be found in various colors and textures.
This is a good choice if you want a very durable mulch that holds its shape and won’t blow away. I especially like shredded bark for defining pathways and mulching sloped areas. It’s ideal if you live in a rainy, windy, or hilly region.
Wood chips are among the most popular types of organic garden mulch, especially for use around trees and shrubs or if you want a natural-looking walkway.
Similar to bark chips but made from the woody part of a tree, wood chips are a material you may already have access to if you have plenty of trees in your yard. When you do your annual pruning, simply feed the unwanted branches through a wood chipper and voilà, free mulch! (You can even do this with your old Christmas tree.)
If you don’t have trees or a wood chipper, you can sometimes find an arborist that will unload a mound of wood chips in your driveway for free (or a nominal fee). This can happen if the arborist just finished a tree trimming job nearby and would rather not haul their load to the local landfill or recycling facility.
So if you spot a tree trimmer working in your neighborhood, stop and ask if they have any plans for the chips. They may be relieved to have a willing taker! Wood chips obtained from tree trimming jobs aren’t the cleanest, since they’re usually mixed in with other tree debris like leaves, twigs, and pine cones. But if you’re just looking to cover some ground, it’s a great way to go.
Sawdust or wood shavings
Like wood chips, sawdust and wood shavings come from trees. They’re less coarse, which makes them ideal for seedlings, small plants, and container plants. Their fine texture sometimes makes them more prone to forming a crust, however, so you might have to gently fluff the sawdust with a rake if it becomes compacted.
Contrary to popular belief, sawdust is not acidic, so it won’t have any effect on acid-loving plants like rhododendrons and azaleas (other than keeping the soil around them moist and healthy).
Pine straw typically refers to commercial bales of aged pine needles, but at home, it can also simply be fallen pine needles collected and used as a mulch. It’s commonly spread around as a landscape mulch to prevent soil erosion but also works great as a garden mulch.
Pine needles are lightweight, take a long time to break down, and you might already have a free source of them if you have pine trees in your yard.
This is another one of those misunderstood mulches because it’s often repeated that pine needles acidify the soil—however, they don’t.
While it’s true that pine needles are acidic when they drop (and are still somewhat fresh), they’re quickly neutralized by microbes in the ground and thus do not turn the soil acidic as they decompose.
Many lawn mowers have grass catchers that collect grass clippings while you mow. Instead of discarding these clippings in your garbage or recycling bins, save them to use as mulch.
A thin layer of grass clippings decays quickly, enriching the soil with nutrients and holding in moisture. This is an easy source of free mulch in summer, and if you don’t need more mulch for the garden, you can just spread the grass clippings over your lawn to rot in place.
Freshly cut cover crops
Growing cover crops in your fall or winter garden after the last of the veggie harvest is always a good idea. It adds nutrients to the soil and keeps the soil structure intact, which helps next year’s crops grow and produce even better!
You can try a cover crop like Austrian winter peas to give the soil a boost (and to snack on through the winter, as the shoots themselves taste like peas).
Once it’s time to cut back the cover crop, which is right after the first pea flowers appear, you can simply chop them all down and leave the vines in place as mulch for other plants (instead of tilling them into the soil).
Surprise, not all organic mulches are plant-based! Sheep wool is a mulch I’ve been experimenting with for a couple of years, and I can say the results so far have been promising.
Although high-quality wool is, of course, best left to make clothes with, not all of the hair sheared from a sheep is suitable for that. For example, the wool on a sheep’s butt can be too dirty or low-quality for this purpose. So, it’s sometimes sold or given away as mulch.
If you can find it from a local farm that’s trying to offload its old wool (which is where I source mine), some advantages of sheep wool mulch include superb insulation (it’s like a warm cozy blanket for your plants!), dense fibers that truly prevent weeds from growing through, high nitrogen content, and slow decomposition.
I like using sheep wool to overwinter my strawberry beds (seen above) and to mulch young tomato and pepper plants in spring (which you can see in my post here about trellising tomatoes). It does have a bit of a “farm smell” after a good rain, but holds up really well through showers, hail, snow, and wind.
I’ve managed to reuse my sheep wool mulch for two to three seasons before it became too ratty; after that, I’ve either buried it under a new planting or added it to the compost pile to finish breaking down.
A by-product of the chocolate industry, cocoa hulls are the roasted shells of cocoa beans. This material has been gaining traction as a garden mulch; it’s sterile (due to having been roasted previously), blends well into the landscape, and does everything you want your mulch to do. Oh, and it even smells pretty yummy to boot!
Please do remember that, like chocolate itself, cocoa hulls can contain theobromine and caffeine. This is toxic to dogs and many other animals, so if your furry friend likes to chew on garden materials, you may need to use one of the other mulches on this list.
Another nice and lightweight option, rice hulls are the protective outer layers of rice seeds. They’re not really edible, so they’re removed during the processing of rice. After this, rice hulls become perfect mulching material if you want a garden mulch that offers good weed control and slow decay.
Because rice hulls are comprised largely of silica, they also amend the soil. To keep them from flying away, just mix the rice hulls with a little compost, sawdust, or other similar material before you dress the soil.
View the Web Story on best types of garden mulch.