Should I add mulch to my garden?
When using the right materials at the right time, mulch can save you both effort and money when it comes to maintaining your landscape. Let’s dig deeper into the mulch pile.
This first-year garden is using two of the best types of mulch; tightly spaced plants and fall leaves.
What is mulch?
First of all, what are we talking about when we use the term mulch? This can refer to any material that is laid on the surface of the soil, usually with the purpose of blocking the germination of unwanted plants (often referred to as weeds).
Why is mulch used in landscaping?
When a new garden is planted, there are usually a lot of gaps between plants to allow room for them to fill out over time. This leaves a lot of soil exposed to seed germination and to the elements - rain, wind and dry conditions can deteriorate the quality of soil and also cause erosion. In order to protect the soil and prevent seeds from germinating, a top dressing of mulch is typically applied. Sometimes a garden is designed with sparse plantings (which is not ecologically ideal), and the gaps will be filled with mulch, which will require annual top dressing. In hot and dry environments, mulch is used to help retain moisture and mitigate soil temperature.
What types of material are commonly used?
Many organic (naturally-occurring) and inorganic (synthetic) materials can be used, but in conventional landscaping practices, landscape fabric and cedar mulch are often used in combination. Other materials include straw, leaves, plant clippings, wood chips, composted materials and more plants! Let’s dig in to some commonly used materials;
Landscape fabric (geotextile, weed barrier): ❌ NOT RECOMMENDED
Not actually considered a mulch, but often used as a mulch underlay.
Rolls of woven or non-woven polypropylene, 3-6’ wide in a variety of lengths.
Provides a physical barrier above the soil while allowing water and air to pass through: inhibits seed germination.
Often covered by cedar mulch, sometimes with river rock.
Advertised as a long-lasting (from 5-50 years!) barrier to cover your soil, but usually begins to break down within 5 years, allowing weeds to grow through.
I’ve recovered countless landscapes that were created with landscape fabric that inevitably failed!
Once the weeds break through, it becomes impossible to remove them by their roots and they just keep getting stronger and stronger (imagine a dandelion that has had its top ripped off dozens of times and subsequently developed a thick tap root many inches deep - and you can’t get to the root because the fabric is in the way!).
As the woven plastic breaks down, long wispy strands become lodged in the soil or blow away in the wind.
This material is not worth using (*except in some agricultural settings).
This cedar mulch garden in a school parking lot is helping to minimize maintenance needs while the newly planted trees get established.
Cedar mulch: ✔️ SOMETIMES RECOMMENDED
Shredded or chipped bark and/or wood of cedar trees.
Provides a physical barrier between soil and air: retains moisture in the soil, inhibits seed germination, mitigates soil temperature, provides a neat and tidy aesthetic.
Decomposes slowly.
Repels many insects.
Depletes nitrogen when mixed into the soil.
Sold undyed (natural), and dyed (brown, black and red).
Dyed mulches should not be used - chemical dyes leach into the soil, and the colours attract heat which can burn sensitive vegetation.
Undyed cedar mulch is best applied at a thickness of 3” near pathways or front edges of gardens to retain a tidy aesthetic. It can also be applied at the back of a garden that abuts a fence, building or other structure that needs to be protected from damp soil.
When applied between plants in newly planted gardens, cedar mulch contributes to overall success of the garden by suppressing weeds and retaining moisture, although it will repel some of the insects that are searching for plants for food and shelter.
Straw, leaves, plant clippings: ✔️ RECOMMENDED
This first year garden is benefiting from the maple tree next to it. The leaf layer will help protect the plants, their roots and the butterflies, caterpillars, moths and bees that call that space home.
Can be gathered on-site (best), from curbside yard bags in the fall, or purchased from a farm or garden store.
Provide a physical barrier between soil and air: retain moisture in the soil, inhibit seed germination, mitigate soil temperature.
Decompose fairly rapidly, requiring annual top dressing.
Plant clippings include perennial stems, small woody branches and grass clippings.
Add nitrogen and other nutrients to the soil.
Start with what you already have on your property - nutrients in the leaves from your own trees are customized to provide the soil what it needs.
Leaves can be piled on the garden in the fall and pulled away from plant crowns as they emerge in the spring (only required with thicker leaves like beech and oak that don’t decompose as quickly as others, like maple and polar). In the spring or summer, partially decomposed leaves can be applied between plants.
If and when you trim back perennial stems, you can lay them behind or in between plants where they will continue to provide habitat for small beings before breaking down and providing nutrients to the soil. Woody debris can be added in the same way.
Wood chips: ✔️ SOMETIMES RECOMMENDED
Often referred to as arborist chips, they are the byproduct of tree trimming and removal.
Provide a physical barrier between soil and air: retain moisture in the soil, inhibit seed germination, mitigate soil temperature, give a neat and tidy appearance to the landscape.
Draw some nitrogen out of the soil as fungi work to break down the fresh wood.
Generate heat as the chips break down - can scorch seedlings.
Wood chips are often used in lawn to garden conversions - a thick pile will smother the lawn and will be plantable after 5-6 months (or a combination of cardboard and a few inches of wood chips).
Can be a free or cheap material to use when creating gardens.
This landscape was transformed from lawn to habitat. It was created with a thick layer of wood chips which can now only be seen between plants.
Composted materials: ✔️ RECOMMENDED
Backyard compost, bagged compost, composted manure, bulk composted pine mulch, composted leaves and grass clippings, composted woodchips, or any composted organic material.
Provide a temporary barrier between soil and air - will break down rapidly.
Balance soil density, improve nutrient retention, slowly release nutrients, absorb water, any add many other benefits.
Composted materials are very beneficial for soil and plants. As a mulch, they are generally not long lasting and therefore will only form a temporary physical barrier.
More plants: ✔️ RECOMMENDED
Ground covers, grasses, sedges, annuals, etc
Plant leaves shade the soil: retaining moisture, inhibiting seed germination, mitigating soil temperatures.
Plant roots go deep: air and water pathways are opened up in clay soils, older roots die off underground and add organic matter to the soil structure, root competition keeps more aggressive plants in check and helps keep tall plants from flopping over.
More variety of plants support more variety of insects.
Plants continue to provide shelter for insects over winter months.
Small gaps between plants are prime locations for some ground nesting native bees.
Plants are the perfect material to use as mulch in the gaps between plants! Since they can be expensive, you can add plants over time, and choose species that spread by seed (ex. Rudbeckia hirta) or by runners (ex. Phlox divaricata), and purchase young plants at the less expensive plug stage, rather than the one-gallon stage.
Why have exposed areas of bark mulch in your garden when you can have wild ginger and wooly bears (larva of Isabella tiger moth)!
So what is the better choice when it comes to mulch?
That depends on the situation and the site. Here are a few things to consider when you are figuring out what type of mulch you will be using:
Avoid landscape fabric.
Use natural, undyed cedar mulch to protect newly planted gardens and structures that abut the garden.
When using a wood mulch on a newly planted garden, apply 3-4” the first year, then allow it to break down and create space for the growing plants and their seeds.
Depending on the material used, mulch should generally be about 3 inches thick, and pulled away from the crowns and stems of plants to avoid rot.
For a lawn to garden conversion, wood chips are an excellent, low cost choice.
The best option is usually to add more plants. They will help keep each other in check, attract and support more wildlife and allow space for ground nesting native bee habitat.
There is no such thing as a no-maintenance garden, no matter what type of mulch you use! Plan to monitor your mulch and remove any unwanted plants as they arrive.
This first year garden is using a combination of wild strawberries, woodland phlox and fallen leaves as a mulch.
In the end, mulch can be a great addition to your garden. It helps plants survive, feeds the soil and its microorganisms, prevents erosion and nutrient depletion and slows the takeover of unwanted plants. Consider the pros and cons of each type before choosing your next method of mulching.
Interested in adding mulch to your land? Not sure how to find native plants for your green mulch?
Contact us and we’ll help you find the right materials for your property.
Resources:
Canadensys - Database of Vascular Plants of Canada (VASCAN)
CBC - Turning your yard into a meadow can save water and time. Here's how to do it
National Wildlife Federation - Ecological landscape design
Pollinator Partnership Canada - Ecoregional planting guides
The Globe and Mail - Is it time to decolonize your lawn?
USDA - Plants Database