Mulch has many benefits, including moisture retention, weed suppression, erosion control, and soil temperature stabilization. This article explains what mulch is made of, what it is used for, and why its a great addition to your flower beds, vegetable garden, and overall landscape.
Mulch is the layer of material that sits on top of the bare mineral-based soil in your yard. The term is generally applied to plant-based landscaping materials applied to manicured landscapes. While the most memorable example of mulch is perhaps the bark mulch in the local schoolyard, there are countless types of mulches available for landscaping use.
Mulching a garden is the gardeners way to mimic the natural soil-building process of wild landscapes like forests and grasslands. These ecosystems add organic matter to the soil through processes such as autumn leaf drop. Read on to learn how you can use mulch to improve your garden and home landscape.
What is Mulch?
So, what is mulch? Mulch is a beneficial surface cover for soil. Popular landscape mulches include bark mulch, wood chips, and composted leaves.
“A mulch is a material used to cover the surface of the soil.”Backyard Bounty: The Complete Guide to Year-Round Organic Gardening in the Pacific Northwest, by Linda Glikeson
Woodland forests naturally create their own mulch with leaf litter and other organic matter on the soil surface. While we can hardly hope to achieve such perfection ourselves, we certainly can mimic this process in our own yards.
What is Mulch Made Of?
The best garden mulches for home gardeners are plant-based organic materials derived from nature. Gardens can be mulched with protective materials such as compost, shredded leaves, arborist wood chips, pine needles, or even tree bark.
“Leaves or needles fall from trees in autumn and mulch the soil all winter. They provide food and habitat, and protect the soil, tree roots, and seeds against the heavy, eroding action of rain and snow and the damage of freezing temperatures.”All The Dirt: Reflections on Organic Farming, by Rachel Fisher, Heather Stretch, and Robin Tunnicliffe
What is Mulch Used For?
Characteristics of a good surface cover garden mulch include:
- suppresses weeds
- retains soil moisture
- prevents erosion
- stabilizes soil temperature
- adds curb appeal
- improves soil fertility
The best mulches can do all of these things! I also like to look for garden mulch options that are economical, environmentally responsible, and locally-produced.
“”Mulch” is a term used for any material that is laid on the soil for some or all of the following purposes: retaining moisture, suppressing weeds, adding organic matter, and protecting against erosion or frost. Mulch can be hay, straw, grass clippings, compost, bark, sawdust, wood chips, or even plastic.”All The Dirt: Reflections on Organic Farming, by Rachel Fisher, Heather Stretch, and Robin Tunnicliffe
“Mulching bare soil reduces water loss through evaporation and prevents germination of weed seeds. If a high- to medium-fertility soil improver is used, this also adds plant nutrients.”Rodale’s Illustrated Encyclopedia of Organic Gardening: The Complete Guide to Natural and Chemical-Free Gardening, by Anna Kruger, Maria Rodale, and Pauline Pears
“We aren’t going about the hard work of gardening to show off big swaths of mulch, but rather well-grown plants.”A Way To Garden: A Hands-On Primer For Every Season, by Margaret Roach
How to Mulch Your Garden
Mulching your garden is an important step in keeping weeds down and stabilizing soil temperatures. Here are the basic steps for mulching a garden.
How to mulch your garden:
- Wait until the soil has warmed up in the spring.
- Soak the soil with water.
- Pull out any weeds from the area.
- Rake the ground to the desired contours.
- Apply any soil amendments.
- Apply mulch. A thickness of 4 inches of mulch is common.
Those are the basic steps for mulching a garden. Here are a few expert tips for applying mulch:
“Thick mulches on the surface of planted areas retain moisture within the soil beneath while also reducing the chances of weed infestation. The soil should be moist, warm and as weed-free as possible before the mulch is applied to the surface.”The Small Garden Handbook, RHS
“After a few weeks, when seedlings are well grown and the soil is warm (and before weeds get going), I move a light layer of mulch back onto the beds. I add more material as it gets warmer and drier, especially around vegetables such as peas and broccoli that like cooler soil.”Backyard Bounty: The Complete Guide to Year-Round Organic Gardening in the Pacific Northwest, by Linda Glikeson
“If I mulched too early, I might smother would-be volunteers, or self-sowns. Mulching too thickly, especially around tree trunks and shrubs (often called “volcano mulching”) is bad for trees; bark wasn’t evolved to live in the dark and damp. Never put mulch right up against the trunks of woody plants.”A Way To Garden: A Hands-On Primer For Every Season, by Margaret Roach
The Best Type of Mulch to Use in Your Yard
Now its time to choose your mulch! So, what kind of mulch should you use? I like to use plant-based mulches – either living groundcovers or composted plant matter. These are generally referred to as organic mulches (in that they are made of material that was recently alive).
I find plant-based mulches to be both aesthetically pleasing on an overall scale and also that they don’t require much maintenance. They’re also among the most cost-effective options and are the somewhat less likely than other options to import contaminants or diseases to my garden.
“Organic matter added as topdressing (mulch) will absorb water and slowly release it to the soil below.”Gardening with Native Plants of the Pacific Northwest, by Arthur R. Kruckeberg & Linda Chalker-Scott.
“The upper soil layers form a resource-rich environment. Sufficient oxygen near the soil surface speeds the metabolic turnover of soil organic matter, releasing carbohydrates and nutrients. Water below the soil surface is more plentiful than above. This cornucopia of resources results in a below ground community with an intensity and diversity of biological activity unmatched anywhere aboveground.”Mineral Nutrition of Plants: Principles and Perspectives, by Emanuel Epstein and Arnold J. Bloom
Types of Garden Mulch
There are countless types of mulch for gardens. Here are some of the most common types of garden mulch.
- Homemade Compost
- Leaf Mold
- Groundcover Plants
- Green Manure
- Arborist’s Wood Chips
- Landscaper’s Mulch
- Bark Mulch
- Plastic Sheeting
- Landscape Fabric
- Gravel and Stone Hardscaping
Let’s start with my favourite mulch – homemade compost!
“What to use for mulch depends on what you can get easily and cheaply.”Backyard Bounty: The Complete Guide to Year-Round Organic Gardening in the Pacific Northwest, by Linda Glikeson
Homemade Compost as a Garden Mulch
Fall leaves, grass clippings, and coffee grounds can be composted at home to create a beautiful, dark compost mulch that looks sharp in well-tended veggie and perennial garden beds. Homemade compost is a top mulch choice for experienced organic gardeners.
Buying Compost for Mulching Your Garden
If you don’t have enough homemade compost to use for mulch, opt for compost from a trustworthy local farm. Farmers spread wood shavings on the floors of their animal stalls on a regular basis as “bedding” for the livestock. Used stall bedding is hot-composted and recycled into landscape mulch.
“My preferred mulch is a composted stable bedding – a local agricultural by-product from horse or dairy farms.”A Way To Garden: A Hands-On Primer For Every Season, by Margaret Roach
Compost can also be purchased in bulk at nurseries and landscape suppliers. This compost is generally a well-composted mix of shredded trees, herbivore animal manure, and excess agricultural products such as grain silage.
“Most regions now have some enterprising farmer or business person who sells finished compost to gardeners for upwards of $80 per cubic yard. You can, of course, make it yourself.”The Permaculture Handbook: Garden Farming for Town and Country, by Peter Bane
Like all organic mulches, compost should be kept about 6″ from tree trunks and building foundations.
Leaf Mold/Composted Leaves as Mulch
Leaf mold is simply compost made entirely from the leaves of deciduous trees. Many gardeners make their own leaf mold simply by leaving piles of shredded leaves to rot for a couple years in a back corner of the yard. Some municipalities also make leaf mold from the leaves collected at the curb-side in the fall.
Here’s what gardening experts have to say about using leaves as mulch for your garden beds:
“My favourite mulch is leaves. They are free, don’t have weed seeds, and break down quickly because they start with a pretty good ratio of carbon to nitrogen. I use leaves as my main mulch on all beds for winter. I stockpile leaves in big plastic bags or bins covered with tarps so I have lots for the following summer.”Backyard Bounty: The Complete Guide to Year-Round Organic Gardening in the Pacific Northwest, by Linda Glikeson
“Collect dead leaves regularly to make into leafmold. Chopping up the leaves can speed the process up. Remove leaf litter from the surface of a lawn, so it does not restrict grass growth.”The Small Garden Handbook, RHS
“Along the central plains of North America, soil was built from the annual contribution of leaves falling from deciduous forests, prairie grasses, and droppings from vast populations of passenger pigeons and bison.”The Legacy: An Elder’s Vision For Our Sustainable Future, by David Suzuki
Living Mulch (Groundcover Plants)
Living mulch refers to groundcover plants. These are generally ornamental groundcovers, although some living mulches are grown as “green manures” and are tilled back into the earth.
“Ground covers act as living mulch, reducing weeding and shading soil, which offers the shrubs or trees above them a cooler, moister root run.”A Way To Garden: A Hands-On Primer For Every Season, by Margaret Roach
Think of living ground cover plants as a soft carpet. Many are evergreen, retaining their foliage even in the cooler shoulder seasons. Look for plants that do a thorough job of covering the ground without requiring much maintenance. Avoid plants that will require lots of annual maintenance or would be a bother to remove if plans change.
“Effective groundcover plants are tough, rapidly spreading ornamentals that will compete successfully with weeds for food, water, and light.Rodale’s Illustrated Encyclopedia of Organic Gardening: The Complete Guide to Natural and Chemical-Free Gardening, by Anna Kruger, Maria Rodale, and Pauline Pears
Here are some great groundcover plant options for living mulch:
- White Moss Thyme
- Bigroot Geranium
- Low ornamental grasses
“”Plants are the mulch,” landscape architect Claudia West reminds us lately, her message both aesthetic and environmental”A Way To Garden: A Hands-On Primer For Every Season, by Margaret Roach
If a temporary green manure is more your thing, here are some good options for planting a temporary “green manure” mulch:
- Various Legumes
Black Landscape Mulch
Black mulch is a favourite mulch product of garden and landscape designers. The dark colour of the mulch compliments plants and really makes the greenery “pop”, especially in newly-installed gardens. It also camouflages any stray garden soil well and is relatively easy to maintain.
Look for a black mulch that is naturally dark in colour (rather than dyed with industrial chemicals). Mulch ingredients like rich compost, charcoal, and certain types of composted manure can add to the dark appearance of black mulch (without added dyes).
“…the right mulch material used well serves several purposes, and is critical in new beds where the living mulch – the plants – hasn’t knitted together yet.”A Way To Garden: A Hands-On Primer For Every Season, by Margaret Roach
Check the ingredients of your landscape mulch to ensure it has only organic, plant-based ingredients (such as OMRI-listed mulch products). Avoid sneaky products that contain biosolids – human sewage sludge. Also avoid mulch where the particles are quite large, as these mulches will not break down effectively in the landscape. It’s all about the plants (not the mulch itself).
Wood Chip Mulch
Coarse woody mulch is perhaps not the most aesthetically-pleasing option, but it can improve compacted soil. Place a woody mulch layer at least 4 inches thick a month or two before attempting to establish new plants. The mulch will improve moisture retention, moderate soil temperature, and allow roots and soil organisms to loosen the ground.
“Heavily compacted soil can be successfully rehabilitated by the use of coarse woody mulch, which naturally restores physical, chemical, and biological function to soil (Chalker-Scott, 2015).”Gardening with Native Plants of the Pacific Northwest, by Arthur R. Kruckeberg & Linda Chalker-Scott.
Types of Wood Chip Mulch
There is, however, a wide variety of wood chip mulches available. The best wood mulches are made from chipped arborist tree prunings, which include all parts of the tree (leaves and all). The prunings are generally composted before sale. The worst wood mulches to use are made from old wooden pallets and other treated wood (and often dyed to be red, brown, or black).
Shredded arborist mulch is often cheaper than compost because nurseries receive the material for free from tree trimmers looking to save on disposal fees at the dump. If you do choose a wood mulch, choose a mulch that includes the whole plant (leaves and all). Straight wood mulches should only be used in areas where plant growth is unwanted, as they rob the soil of nitrogen required by plants.
Organic commercial mulches are also available, both in small bags and for bulk mulch delivery. Look for a wood mulch that’s certified to be free of chemicals like pesticides, fungicides, and herbicides. Mulches that have been dyed with synthetic dyes should also be avoided.
Bark mulch products are made from the chipped bark of evergreen trees. Some of these bark mulches consist of small pieces and are already pre-composted when you buy them. Others consist entirely of large chunks of long-lasting wood such as cedar.
Cedar mulch lasts much longer than other types of bark mulch because cedar is resistant to decay. Cedar decomposes much more slowly than other common types of wood or composted mulches. It also has a nice warm natural colour and fresh scent. Avoid “cedar mulch” made from other (cheaper) types of wood that have been dyed to look like cedar.
Bark mulch, like all wood-based mulches, uses up nitrogen in the surrounding soil as it slowly decomposes. This can “rob” nearby plants of the nitrogen they need. If using bark mulch, your plants will likely need regular application of a quality organic fertilizer.
Inorganic mulches such as plastic or textile sheeting are also used in some large market gardens and small organic farms. Sheeting is generally used as a utility mulch in these commercial applications as it doesn’t really enhance the look of the garden. If you just want to grow rows of flowers for bouquets or veggies to can/sell, and don’t care much about the plastic showing, sheeting may be right for you.
“Both organic and inorganic mulches […] help retain soil soil moisture by reducing evaporation.”Gardening with Native Plants of the Pacific Northwest, by Arthur R. Kruckeberg & Linda Chalker-Scott.
Black plastic sheeting is generally considered an inorganic sheet-type mulch. Other synthetic sheet mulches include landscape fabric and other geotextiles.
Another great use for sheet mulch is to clear weeds from a large patch of ground. Sheet mulch like black plastic can be used to smother weeds by blocking out the light.
Paper Product Mulch
Paper creates a biodegradable sheeting-type mulch. Old newspapers, cardboard, or even paper on a roll can be used as short-lived mulch. Paper usually must be layed in thick layers, moistened, and covered with loose mulch to hold it in place.
“Sometimes when prepping a new area, or rehabbing one that’s weedy, an organic mulch alone may not suffice to keep troubles at bay until the desired plants fill in. An underlayment of thick layers of black and white newspring or a sheet of brown corrugated cardboard will add the extra oomph.”A Way To Garden: A Hands-On Primer For Every Season, by Margaret Roach
What is a Yard of Mulch?
A yard of mulch is a unit of measure referring to a volume of one cubic yard of loose landscaping material. A yard is the volume in a 3′ x 3′ x 3′ cube of space. A cubic yard is similar in volume to – but slightly less than – one cubic metre.
The photo below shows a yellow loader at a bulk mulch landscaping retailer. One loader bucket of mulch, as shown in the photo below, is about one yard of mulch. One loader bucket of mulch – or one yard of mulch – is enough to pretty much fill the box of an average North American homeowner pickup truck.
Types of Mulch to Avoid
Avoid garden mulch made from industrial byproducts such as lumber wood chips or rubber tires. Any chemically-dyed mulches are also a no-go. Wood chips, sawdust, and root mulches have also been known to import artillery fungi which love to shoot sticky dark spores onto siding and fences (not so nice…).
Recycled industrial materials like rubber mulch are generally discouraged by home gardeners, as they can leach industrial chemicals into your garden (and make it smell like a hot racetrack in the summer). There are appropriate ways to recycle rubber tires (including into surface coverings) but home garden mulch isn’t one of them. If you have to pay a bunch of money to get rid of something (and go to a specialized disposal area), it’s generally not worth paying for as garden mulch.
Chemically-treated natural mulches should also be avoided. This includes many wood mulches made from scrap lumber such as pallets. Some of this wood has been treated with chemicals like fungicides which are detrimental to garden health. Wood mulch made of scrap wood chips is often dyed as a way to sell it as a higher price. Avoid mulches that look like they’ve been dyed green, red, or black.
Lastly, avoid mulches which may contain living weed seeds. This includes hay, straw, poorly-composted animal manures, and poorly-composted yard waste.
“More is known about the deep oceans or polar ice caps than about the processes that occur right beneath our feet in the soil.”Mineral Nutrition of Plants: Principles and Perspectives, by Emanuel Epstein and Arnold J. Bloom