Slate chips are flat, angular fragments of natural slate used as a permanent decorative ground cover in beds, borders and paths. They stay where you rake them, they never decompose, and a 40 lb bag covers about 2.5 sq ft at a 2 inch depth, which is the number most projects are budgeted from.
Key Takeaways
- Size: our slate chips run approximately 1 to 3 inches, flat with irregular angles, so they lock together instead of rolling like round river rock.
- Color: gray when dry, turning deep black when wet, which changes the look of a bed after every rain.
- Coverage: one 40 lb bag covers 2.5 sq ft and one ton covers 125 sq ft, both at a 2 inch depth.
- Lifespan: slate does not rot, so there is no annual top up the way there is with wood mulch.
- Scarcity: slate sits in the final 1% of US crushed stone production, behind limestone, granite and traprock, so supply is a specialty item rather than a bulk commodity.
What slate chips actually are
Slate is a fine grained metamorphic rock that splits along flat planes. That cleavage is the whole reason it works as a ground cover: crushing it produces flat plates rather than cubes, and flat plates knit together into a stable mat. Round gravel of the same diameter shifts underfoot and migrates out of beds onto the lawn.
The material is a genuine niche product. In 2024 the United States produced about 1.5 billion tons of crushed stone valued at $26 billion, of which roughly 70% was limestone and dolomite and 14% granite; slate appears only in the last 1% alongside marble and shell, according to the US Geological Survey. Slate destined for cut applications is covered by a separate standard, ASTM C629, which sets absorption, abrasion and rupture requirements for dimension slate and explicitly excludes crushed and broken stone. Landscape chips are that excluded product, so judge them on shape, size grading and cleanliness rather than on a spec sheet.
Flat slate plates knit together and stay in place, unlike round gravel of the same size.
Sizes and finishes: what to look at before you order
Three things separate a good load of slate chips from a disappointing one. The first is size grading. A mixed 1 to 3 inch grade reads as natural and compacts well; anything smaller tracks indoors on shoes, anything larger becomes uncomfortable to walk on. Jumbo slate chips exist for large commercial beds where scale matters more than comfort.
The second is dust content. Freshly crushed natural slate carries fines that wash to the surface in the first heavy rain and gray out the color for a season. The third is consistency of tone. Slate is quarried, not manufactured, so a black slate chip from one batch may lean charcoal and the next may lean blue gray. Order the full quantity at once when the color has to match across a whole yard.
Our slate chippings are the flat 1 to 3 inch grade, and the rest of the landscaping stones range covers the pebble and gravel formats people usually compare them with.
How much slate you need: the math
Measure the bed in feet, then use length x width x depth. A bed 20 ft by 4 ft at a 2 inch depth is 80 sq ft, which is 32 bags of 40 lb or a little over half a ton. If you prefer volume, divide cubic feet by 27 to get cubic yards, then convert with the coverage figures.
Depth drives everything. 2 inches is the standard for beds and borders. Go to 3 inches on paths and high traffic areas, where the extra depth both suppresses weeds and stops the soil from showing through when the material spreads. A 1 inch decorative topping only makes sense over an existing compacted base.
Two practical notes on ordering. Bagged material is easier for a small bed and for anything you have to carry through a house or down steps. Bulk delivery by dump truck is cheaper per ton once you cross roughly a ton, but the truck needs a drop point it can reach and a surface it will not damage, so confirm access before the order rather than on delivery day.
Coverage by depth, based on 2.5 sq ft per 40 lb bag at a 2 inch depth.
Slate chips against wood mulch and river rock
Wood mulch feeds the soil as it breaks down, and that is its real advantage. The cost is that it breaks down: most beds need a top up every year or two, and the color fades within a season. Slate does not decompose, which is why it is used where the design is meant to hold for a decade.
Against river rock, the difference is mechanical. Round stone rolls, so it works its way onto lawns and driveways and is awkward underfoot. Flat slate stays put and takes foot traffic far better, which is why it is the usual choice for a path between pavers or stepping stones.
Slate also holds heat. The US Environmental Protection Agency notes that hard, dry, dark surfaces absorb and re-emit more solar energy than vegetation, and that this pushes daytime urban temperatures about 1 to 7°F above outlying areas. On a small scale, a wide expanse of dark slate against a south facing wall behaves the same way. Keep it away from thin skinned plants that struggle with reflected heat, and use it where that thermal mass is neutral or useful.
Wet slate turns almost black, which is why it is a standard surround for water features.
Where slate chips work best
Slate earns its keep in low maintenance positions where organic mulch is a nuisance: under decks and stairs, around mature trees, along foundation strips, in narrow side yards, and as a dry border where a mower cannot reach. It is also the standard surround for water features, since it does not float, stain or rot when it is constantly wet, and the wet black tone is part of the effect.
It is a poor choice in two situations. The first is a bed of annuals that gets dug over every spring, where the chips end up mixed into the soil. The second is a slope steeper than roughly 1 in 4 without edging, where any loose aggregate migrates downhill. Anywhere rain has to soak in rather than run off, a permeable stone layer helps: the EPA notes that permeable surfaces let rain and snowmelt seep through instead of shedding it toward the street.
Installing slate chips
Strip the existing vegetation and roots rather than burying them, then set the grade so the finished stone sits slightly below any adjacent hard surface. Install edging before the stone, not after; without it, the boundary between bed and lawn disappears in two seasons.
The weed barrier question deserves a straight answer. Landscape fabric is sold as permanent weed control, and it is not. North Carolina State Extension summarizes research going back to the 1980s showing that fabric topped with mulch becomes just as weedy as bare mulch, because seed germinates in the debris that collects above it. Under stone the calculation is different from under bark: fabric mainly stops the chips from sinking into soft soil. Treat it as a separation layer, expect to weed the surface anyway, and choose a woven geotextile rather than thin plastic sheet.
Spread in two passes, rake level, then walk the surface to settle the plates. A light rinse removes the quarry dust and gives you the finished color immediately.
Maintenance through the seasons
Slate needs a rake, not a schedule. Redistribute the chips once or twice a year to even out traffic wear, and pull the few weeds that root in accumulated leaf litter before they seed. Blow leaves off in the fall rather than letting them break down into the stone, since that organic layer is what creates a weed bed on top of an otherwise inert surface.
In winter, avoid pushing a shovel blade through a slate path; a plastic shovel held slightly high, or a broom, keeps the material in place. Rock salt does not damage slate, but the runoff harms adjacent plantings, so keep de-icer on the walkway rather than the bed. Every few years, top up the thinned areas rather than replacing the whole surface. Compared with the annual mulch cycle, the maintenance profile of a slate bed is mostly nothing.
Know your square footage? We'll tell you exactly how much stone to order.
Depth changes everything: the same area needs twice the stone at 3 in than at 1 in. Send us your dimensions and our advisors confirm the quantity before you buy, in bags for a small bed or by the pallet and full truck for a whole yard. Over 50 hand-polished natural stone varieties, shipped everywhere in Canada and the USA.
Questions about slate chips
How many bags of slate chips do I need for 100 sq ft?
At a 2 inch depth, 40 bags of 40 lb, since each bag covers 2.5 sq ft. At a 3 inch depth, budget about 59 bags, or roughly 1.2 tons.
Do slate chips fade?
No. The color is the rock itself, so it does not bleach the way dyed wood mulch does. What changes is surface dust, which washes off, and the temporary darkening after rain.
Can I put slate chips over an existing gravel driveway?
You can top an established, compacted base, but slate is not a driveway wearing course. Vehicle tires break the plates down and push them aside. Keep it on paths, beds and pedestrian areas.
Is slate safe around plants?
Yes for established shrubs, trees and ornamental grasses. It is chemically inert and does not change soil pH in any meaningful way. Give thin skinned annuals a mulch that holds moisture instead, and leave a small gap around trunks and stems.
What is the difference between slate chips and slate chippings?
Nothing. Chippings is the British term for the same crushed natural slate; North American suppliers list the same product as slate chips or slate mulch.