Key slate mulch facts
Availability – regional
Cost – low
Ornamental value – deep gray
Ornamental layer – 2-4 in (5-10 cm)
Soil enrichment – doesn’t make soil alkaline
Renew rate – every three years, dig out & sift
- Read also: other types of mineral mulch
Advantages of slate mulch
Slate mulch stands out for its ornamental properties and flat, surface-covering capabilities. Also a natural source of iron, its gray and sometimes amber color is what makes it radiate a feeling of rough, harsh nature.
Slate mulch has many advantages, both as an ornament and from a practical point of view.
- Avoids sprouting of weeds
- Reduces watering frequency
- Very long lasting
- Surface-covering and unalterable
- Can’t be blown away
- Regulates soil temperature: cooler in summer, warmer in winter
Depending on where the slate comes from, slate mulch color can be pencil-gray, blue, black and even purple or green. This is due to differences in chemical composition of the rock.
Since it reflects light upwards, it helps provide light for sun-loving plants even when not planted in full sun.
- Reflecting light also has another beneficial effect: it’s a natural way to repel thrips!
How to use slate mulch
Simply layer the mulch out in a layer about 3 inches thick (8 cm). It’s ok if it isn’t a very even layer.
Precautions when spreading slate mulch
To avoid breathing in slate dust, wear a dust mask.
- Another solution is to drench the pack or pile of slate mulch with water. Dust won’t fly out.
Slate chips are sharp-edged. Wear gloves to avoid wounds and make spreading easier.
How to spread slate chips
A sturdy rake will do the trick.
- Short-toothed metal rakes will be more useful than long, leaf-clearing rakes.
- Otherwise, a few teeth might break off, especially if the rake is made of plastic.
Use a strong pail with a strong handle.
- Don’t overload the pail, only fill it up with about 10 or 15 pounds (2 to 3 kg) per load.
Best is to set the bag of slate mulch on a strong work bench.
- Slit the pack on the side, and scoop material out to make it fall into the pail at the side of the work bench.
- To save efforts, place a chair or bench so that the bucket rests just under the side of the table. You can now use two hands to scoop slate mulch!
- Working at table height is a basic practice of raised gardening, guaranteed to make gardening easier!
Re-applying slate mulch
After three or four years, soil and dirt tend to come up and cover the slate mulch. To bring the flower or shrub bed back to its original elegance, you can either chose to buy new slate mulch, or to dig up the previous one and clean it up.
Adding fresh slate mulch
A layer of fresh slate mulch needn’t be as thick as the original layer.
- Sometimes just an inch or two is enough. (3 to 5 cm)
Recycling older slate mulch
You can recover your previous slate mulch relatively easily.
- Dig the soil up down to a depth of 4 to 6 inches (10 to 15 cm).
- Use a mesh wire drum or a half-inch sieve frame (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 immediately (moisture attracts insects and possibly snakes).
- Before placing the slate back in the flower bed, consider adding a layer of nutritious plant material such as wood chip mulch or ramial wood chips first.
- Cover this fresh plant material with your cleaned-up slate mulch. Watch as your flowers burst with blooms!
Recovering your slate is a great and inexpensive way to get your garden look astounding again. You’ll be maximizing your past investment for years!
Where to find slate mulch
It’s usually possible to find slate mulch in garden stores.
Rooftops in some areas are traditionally covered with slate shingles. This is particularly true in Europe and in some parts of Maine, in the North-East United States.
Get in touch with a local roof-builder to recycle their waste such as broken shale shingles, old roof shingles being replaced, etc.
It’s a great way to recycle in the garden!
Slate mulch is very similar to shale mulch. Any supplier having one might also be able to have the other.
Smart tip about slate mulch
If you want your hydrangeas to bloom in a beautiful blueish tint, mulch its base with slate.
Slate naturally releases alumina, which changes the flower’s color.
Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Japanese-style garden with slate by Florentaise
Slate mulch and log couch by Wildroof under © CC BY 2.0
Layer of slate mulch by keriluamox under © CC BY-SA 2.0