Shale - mineral mulch and ornaments for the garden

Shale, a mineral mulch, is very ornamental. It lasts a lifetime.

Key shale mulch facts

Availability – common
Cost – low
Ornamental value – brown or tan

Ornamental layer – 2 to 4 in (5-10 cm)
Renew rate – every 3-4 years

Soil enrichment – brings the soil to neutral

Shale is a type of gravel related to slate. It is a sure fit to any prized location in gardens and pathways. A few sacks of shale mulch will last a very long time, especially if you sift soil and dirt out from the mulch every few years.

Advantages of shale

Shale has all the advantages of mineral mulch, with the added benefit of a neutral pH.

Extremely ornamental mulch
Durable: doesn’t burn, break down, rot and does resist all types of weather (wind, rain, etc…)
Neutral pH
Saves on watering since it reduces evaporation
Eliminates weed growth
Protects against freezing
Excellent for landscaping

Thanks to all these advantages,

You’ll spur root development and growth of your plants.
Your blooms will be more abundant and your garden even more wonderful!

Brownish or violet-gray and very stable as years go by, this mulch is particularly well suited to all kinds of beds: trees, shrubs, green plants and flowered plants, both outdoors and indoors.

Here, a Eucomis regia looking a lot like spurge, growing in shale.

Shale mulch color

Color depends on how much iron oxide the rock contains.

Higher amounts → reddish-tan color
Lower amounts → grayish “slate” color (!)

Shale and pH

Shale heavily influences the pH of soil, bringing it closer to neutral (pH 7). If you have very acidic soil, using shale will bring the pH back to normal within a couple years in the immediate vicinity. Great to change the color of your hydrangea from blue (acidic) to pink (neutral)!

Difference between shale and slate mulch

The main difference between shale mulch and slate mulch is that shale isn’t as shiny or reflective.

Shale mulch has a duller sheen to it than shiny slate when dry.
The color transformation when wet is much more amazing! Stroll in the garden after a rain to savor the deep, rich color of shale.

How to use shale for mulch

A layer about 3 inches thick (8 cm) is perfect. Any thinner and weeds will get through. Any thicker will make the soil heavier and more compact.

Precautions when working with shale mulch

To avoid breathing in rock dust, wear a dust mask.

Another solution is to drench the pack or pile of shale with water. This will keep the dust down.

Although shale is rather blunt, you should wear gloves to avoid wounds. Working with gravel takes a toll on skin and gloves make spreading easier.

How to spread shale shards

Pile small mounds of shale gravel every foot or foot-and-a-half (30 to 45 cm). Rake the mounds flat afterwards.

Use a sturdy rake that won’t break with this heavy material. Also use a strong bucket with a thick handle.

Don’t overload the container.
Since you’re going back and forth, only carry around 10 or 15 pounds (2 to 3 kg) per load.
Bring the bulk of the shale mulch closer with a wheelbarrow.

Re-applying shale mulch

Soil and dirt will naturally rise up between shale gravel, in time. To bring the flower bed back to its initial appearance, two options are available:

you can either chose to buy new mulch,
or dig up the previous one and clean it up.

Adding fresh shale mulch

A layer of new shale mulch doesn’t need to be as thick as the first layer.

An inch or two is enough (3 to 5 cm)

Recovering old shale mulch

You can recycle your previous stone mulch relatively easily.

Dig the soil down to a depth of 4 to 6 inches (10 to 15 cm).
Use a mesh wire drum or a half-inch sieve frame (about 1 cm sieve) to sift the soil and dirt out. Drums used to topdress lawns are perfect for this.
Small batches make work easier, maybe up to 10 pounds (5 kg) in one go.
To get that shiny look back, rinse with a garden hose.
Set out to dry if not using it again right away (moisture attracts insects and even snakes).
Before placing the shale back in the flower bed, consider adding a layer of nutritious plant mulch first.
Cover this fresh plant material with your cleaned-up shale mulch.

Recovering old shale mulch is a great and cheap way to get your garden look astounding again. Your past investment will last forever!

Landscaping with shale

Shale is a wonderful material to work with. From building a rock wall to creating a “dry river”, it’s a great mineral to decorate your garden.

The colors pair well with themed gardens, such as blue and white gardens. It also has a timeless look that sublimes arbors and wrought iron garden ornaments.

Where to find shale mulch

It’s always possible to find shale mulch in horticulture centers.

Shale is also known for another fact: it contains a small portion of organic compounds called kerogen. Energy companies try to extract this oil from shale in a process called fracking. It’s a disaster when done in pristine environments.

Using discarded shale in the garden, though, is a way to reduce the negative impact of this practice. It’s a small way of helping recycle in the garden!

Shale occasionally has fossils in it – keep an eye out for those reminders of the past!