Low mulch creates magic in the garden Find out why you should mulch your garden beds and what materials are right for your site.
Almost all gardening experts recommend using mulch around new and existing plants, but why? Mulching has many benefits for your garden, but it can also cause problems if used incorrectly.
In nature, mulch forms naturally from fallen leaves, dead grass, and other materials collected on
the ground. This layer of decomposed or decomposing material provides a home for beneficial organisms that break down the organic materials in the mulch into simpler components that plants can use. This natural mulch also provides a buffer layer, reducing the impact of rainwater falling on the soil, reducing soil compaction and erosion, and improving water absorption. Mulch helps
alleviate drought conditions by creating a barrier against evaporation. It also acts as an insulator to mitigate extreme changes in soil temperature. Mulch covers the soil surface and blocks seeds that need exposure to light to germinate, as is the case with many garden weeds.
Mulches used in home landscapes have many of these natural functions, some better than others. Mulches can also serve as a design element, adding color and texture to floors. Determining the
best mulch to use depends on your location, the type of landscaping you are doing, and your aesthetic goals.
Type of mulches
Here we list the many materials used for mulch along with their pros and cons. It is roughly divided
into organic materials, living materials, single biomass and inorganic materials (minerals, synthetic
materials, etc.).
Organic material
living mulch – Living mulch consists of low-growing plants that form a dense layer of ground cover once established. It can be a single species or a variety of plants forming an interlocking matrix. This is most similar to those encountered in grassland or forest environments. Examples
of living mulch plants include sedum, lady’s mantle (Alchemilla mollis), moss phlox (Phlox subulata), golden ragwort (Packera aurea) and green and gold (Chrysogonum virginianum).
Pros – Retains moisture, reduces erosion, allows moisture penetration, supports beneficial organisms, provides good temperature regulation and great aesthetics. Weed suppression is dependent on planting density.
Cons – Takes time to develop thick growth and requires more maintenance while settling. It can be difficult to tell the difference between desired plants and unwanted plants (weeds).
The shredded bark used in this sloping garden in Maryland tends to resist being washed away by interlocking.
Shredded tree bark – It is made from the outer layer of wood and is a by-product of the timber industry. Depending on the type of tree, the nature and appearance are different. Trees used for
shredded bark mulch include hardwoods, cedar, hemlock, pine, and redwood. Available types vary by location. Coarsely shredded grades last longer, but don’t look as good as fine grades in some environments. Over time, the shredded husk decomposes, enriching the soil with organic matter. Sometimes chipped or shredded wood resembles dyed and shredded bark covering, so read product
information carefully.
Pros – Very well weed suppression, good moisture and temperature control, allows moisture penetration and breaks down over time to build up the soil and support soil organisms. Aesthetics
depend on the type and grade used.
Cons – Needs to be replenished regularly (1-3 years) and fades over time. If applied too thickly, coarse grades may be washed away and fine grades may be squeezed out.
A large piece of bark in the Ohio yard complements the outdoor furniture and separates the seating area from the surrounding bunks.
Nuggets of pine bark – These are actual chunks of pine bark and come in a variety of sizes. Larger pieces last longer but are rougher in shape and tend to drift or move around the garden.
Pros – While similar to shredded bark, chunks of pine bark break down more slowly than other wood and bark products and can retain their color for years.
Cons – Large pieces tend to move around in the landscape, are harder to walk than chopped produce, and have a rougher appearance.
Finely ground tree mulch provides an even-looking backdrop to accentuate the plant forms in
this Indiana garden.
Chopped or broken trees – This material comes from a variety of sources, including landscaping waste, sawmill waste, arborist shavings, and recycled wood from pallets and building materials. They can be natural colored (shades of brown and gray) or usually dyed black, brown or red. Some salvaged wood may be contaminated with old paint, preservatives or industrial chemicals, so it’s
best to find out where the wood came from.
Partially composted, virgin source chopped wood is an all-around option. Arborist chips heat up while the foliage and green matter they contain decomposes, but the resulting matter, while crude, makes good mulch and may cost little or nothing.
Pros – Humidity and temperature control, good weed suppression, water absorption, erosion control, available in a variety of colors. Timber from pristine sources degrades over time, contributing to soil health. Best used in fixed beds around trees and shrubs. Growing plants from vegetable gardens or seeds is not a good option.
Cons – Requires regular replenishment and may contain contaminated materials. Aesthetics vary
by material and grade.
In this garden, composted leaf mulch is used as a surface.
Compost – High-quality organic compost is the healthiest mulch you can add to your garden soil. It provides many organic substances and nutrients that soil organisms can pass on to plants. Therefore, it has a shorter lifespan as a mulch material and needs to be replenished more frequently in order to continue to perform well in weed suppression, moisture retention and temperature
regulation. Its best use is in the vegetable garden as a fillet where plants grow quickly and provide the benefits of living mulch.
Pros: Feeds plants well, improves soil quality, provides good early weed control, provides good moisture and temperature control. Dark in appearance and good in texture.
Cons: Short lifespan and requires annual or more frequent use. Poor quality compost may contain weed seeds. Compost can shade the soil and slow the germination of existing seeds, but it can also promote the germination of new weed seeds that fall on it.
This garden path in Colorado is using cut grass.
Grass and leaves – Cut grass and chopped leaves are essentially free mulch, which also saves on disposal costs. However, to avoid problems, make sure that the lawn you use is free of lawn chemicals and weed seeds. Mowed grass is high in nitrogen and is best used in vegetable gardens.
Before putting it back into the garden as mulch, grass should be sun-dried for a few days to make sure the rapidly decomposing material doesn’t burn delicate vegetables. Leaves should be shredded
to minimize matting and allow water to move through the layers. Shredded leaves are easier to spread, look more even, and decompose faster, benefiting the soil.
Pros – It’s free, replenishes the soil with nutrients, holds water well and regulates temperature well.
Cons – Decomposes quickly and requires regular replenishment. Grass and larger leaves will compact and absorb water more slowly. The lawn can be contaminated with weed seeds, needs to be “cured” to prevent burning, and can smell if applied too thickly.
Beds of soft pine needles accentuate rough stepping stones on this woodland trail in Pennsylvania.
Pine needles – Pine needles form an excellent mulch, best suited to woodland settings with acid loving evergreens and shrubs. High resin content results in slow degradation and needle-shaped compression resistance. Pine needles cover the aisles nicely. However, it’s not very good on slopes as it can be slippery when wet.
Pros – long life, good water permeability and warmth retention, good weed control and good moisture retention. It gradually improves soil quality over time and is economical and fragrant in
areas rich in pine trees.
Cons – Only one color and can be slippery when wet, especially on compressed surfaces.
Black slate gravel is used as mulch in Milwaukee gardens.
Inorganic Materials
Stones and gravel – Many plants grow well in and around rocks. Stone is the most durable natural mulch material. It works best in dry or harsh conditions where organic matter breaks down or flies off quickly. Stone tends to be hotter than organic materials. Especially for dark colors. Light colored stones reflect a lot of light upwards and can burn the undersides of leaves on plants not adapted to such conditions. When installing the stone mulch, it is recommended to lay permeable geotextiles to prevent soil and rock from mixing. Also consider other inorganic materials such as broken shells, polished glass and ceramic shards.
Pros – Durable, available in a variety of colors and textures, has good water permeability and soil protection. Weed control depends on how you prepare and prevent organic matter (leaves and grass
clippings) from accumulating in your beds.
Cons – Heavy, adds only micronutrients to soil, needs to be controlled with rims or some edging. Depending on the esthetics, the bed may need to be cleaned from time to time.
This geotextile layer controls weeds and prevents soil from mixing into stone paths.
Geotextiles – Geotextiles, also known as landscape fabrics, are made from polyethylene fibers that are woven or spun into materials with very small pore sizes. It allows water and dissolved gases to enter the soil but prevents weeds from growing underneath. Its best use in the garden is as a separating layer between the soil and mulch, especially when used with stones or gravel. It is also
used under paths and in French drains to prevent soil from mixing with the aggregate. As a surface
layer, it has poor aesthetics and relatively short service life. One problem with garden beds is that while they inhibit weed growth from below, the roots of plants growing on the fabric can penetrate and cannot be removed without cutting the affected geotextiles.
Pros – Good water retention, excellent soil barrier and good weed barrier.
Cons – Unattractive and short lived unless covered with another material. They will need to be cut off to allow further planting, and they may re-emerge over time if they are not well secured when installed.
Here, plastic sheeting from years ago remains in place of the new channels (between the flags), but has been removed where the hosta grafts were installed. Later everything was covered with shredded bark mulch.
Plastic sheeting – Plastic film mulches are primarily used in agricultural settings, depending on the specific crop or season. It is rarely used in landscaping, but is used as an understory plant in some facilities. It effectively suppresses weeds and retains water and air while containing the soil below. Cutting this layer can be messy if you need additional planting. The best landscaping uses are in areas where no vegetation is growing and water ingress barriers are not an issue.
Pros – Long lasting, stops soil evaporation and weed growth underneath.
Cons – suffocates the soil and prevents water ingress. It is unattractive unless you cover it with
another material.
Here, we use brown rubber mulch and drought-tolerant plants in a relatively low-maintenance
California garden.
Rubber – Most rubber mulch comes from recycled tires that have been treated and shredded to
remove wire rope. These come in a variety of shades, from earthy tones to colors like blues, greens,
and reds. Because this mulch is synthetic, it degrades less than organic materials. For this reason,
aside from suppressing weeds and controlling moisture, they provide no nutrients to the soil and
are of little benefit to plants. As with stone and gravel mulch, rubber mulch should be used with a
geotextile liner to keep it clean and easy to remove later if your preference for material or color changes. If low maintenance is more important than plant growth and the exotic color of the ground plane is an important part of your design, this could be a good choice. Playgrounds use rubber covers. However, some groups question whether it is completely safe.
Pros – Durable, consistent appearance, stays in place, offers good water permeability and weed
suppression, and is available in a variety of colors and textures.
Cons – They do little to help soil fertilization or plant health, and cost more per cubic foot than
wood or bark products. Due to the large number of manufacturers, quality may vary. Concerns
about leaching of chemical additives and residual steel code remain.
Mulching technology
Mulching has many benefits, but it can cause problems if used incorrectly.
Timing – A good time to apply mulch is in the spring, after the soil has warmed up, after fertilizer
or compost has been applied, and before the start of hot or dry periods. Adding mulch in the fall is
great for protecting tender plants on the hardy edges of the area. However, if your plants are cold adapted, waiting until the ground freezes before winter mulching can prevent frost and provide
better flowering for plants that require cold winters.
Don’t pile the mulch too deep – A layer of 2 to 4 inches deep is recommended for most mulches.
Applying too thickly can restrict airflow to the soil and suffocate plant roots. A layer that is too thick can also become damp and foul-smelling due to the growth of anaerobic bacteria. A layer of organic mulch that is too thick is slow to decompose and prone to compaction.
Keep the mulch away from the stem – One of the most obvious misuses of mulch is “volcanic
mulch”. This is where the mulch is piled up in a cone around the base of the tree. When this happens, the bark remains wet, which can lead to a condition called bark rot. Also, some trees will put out new roots in these cones that encircle and tighten the tree. It usually takes several years. The same goes for shrubs and perennials. Covering the roots can cause crown rot. In general, mulch should be pulled back 2 to 4 inches from the trunk or crown of the tree or shrub.
Check the quality – Each mulch listed here has multiple vendors, so quality can potentially vary.
If you’re working on a big project and have questions, get a material sample and see for yourself.
Which color and feel are right for me? Does it smell strange? Do you see things that don’t belong?
If you don’t like it, find another provider.
