Plum Slate vs Grey Slate: Colour, Cost & Best Uses Compared

Plum slate has a deep burgundy-purple tone that sets it apart from every other aggregate on the market. It's the best-selling slate colour across UK suppliers — and for good reason. The colour is rich and warm without being garish, and it creates immediate visual contrast against green foliage, cream paving, and red brick.

Grey slate is a cool, neutral blue-grey that blends quietly into the background. It complements any colour scheme without competing for attention, making it the go-to for minimalist and contemporary designs where the planting or hardscaping should be the focal point.

The Wet-vs-Dry Test

This is where the two stones diverge most dramatically:

• Plum slate when wet: The colour intensifies significantly — dry plum is a muted aubergine, but after rain it deepens to a rich, saturated burgundy. Many buyers choose plum specifically for this wet-look effect. It's the most dramatic colour shift of any common aggregate.
• Grey slate when wet: Stays largely the same — perhaps a shade darker, with a slight sheen. There's no dramatic colour shift, which is actually a plus if you want consistency regardless of weather.

Property	Plum Slate	Grey Slate
Dry colour	Muted aubergine/brown-purple	Cool blue-grey
Wet colour	Deep saturated burgundy	Slightly darker grey
Colour shift (wet)	Dramatic	Subtle
Warmth	Warm-toned	Cool-toned
Visual impact	Statement — draws the eye	Recessive — blends quietly

If you want the aggregate itself to be a feature, go plum. If you want the stones to recede and let the planting or paving dominate, go grey.

Good news: plum and grey slate are priced almost identically. Both come from UK quarries (primarily in Wales and Scotland), and the supply chains are mature enough that there's no premium for either colour.

Format	Plum Slate	Grey Slate
850 kg bulk bag	£104–£220	£104–£220
20 kg bag	£5–£7	£5–£7
Coverage at 50 mm depth	~12–14 m² per tonne	~12–14 m² per tonne

The price variation within each colour is down to supplier, haulage distance, and whether the price includes VAT. Always check whether a quoted price is ex-VAT or inc-VAT — a £104 + VAT bulk bag actually costs £124.80 delivered.

Both are available in 20 mm and 40 mm sizes. The 20 mm is the more popular seller — it's versatile enough for paths, borders, and beds. The 40 mm is better for larger areas, feature mulch around mature trees, and creating visual scale in big gardens.

Use the gravel calculator to work out exactly how many bulk bags you'll need for your area before ordering.

Where Plum Slate Works Best

• Cream or buff paving: The burgundy tones pop against light sandstone, Indian stone, and buff-coloured porcelain. It's a classic combination in cottage and traditional gardens.
• Green foliage contrast: Plum creates a rich, warm base for evergreen shrubs, box hedging, hostas, and ferns. The colour contrast between green leaves and purple stone is striking without being garish.
• Cottage and traditional gardens: Plum's warmth suits red brick, timber, and natural stone — the materials typical of period and rural properties.
• Garden ponds: Plum slate is fish-friendly (chemically inert, won't affect pH) and its colour looks superb at the water's edge, especially when kept permanently wet.

Where Grey Slate Works Best

• Modern grey paving: Grey slate is the natural partner for porcelain patio tiles, composite decking, and sawn granite. Everything tonal, everything coordinated. Our Black Slate Gravel and Black Tumbled Slate Gravel deliver a deep grey-black that's striking in contemporary settings.
• Contemporary design: Anthracite fencing, rendered walls, aluminium planters — grey slate fits the entire modern material palette without clashing. For the darkest option, Black Basalt Gravel is an angular volcanic alternative worth considering.
• Minimalist gardens: When you want clean lines, architectural planting, and zero visual noise, grey slate provides a consistent, uniform backdrop.
• Front gardens: Grey is the safest colour for front-of-house projects where you want kerb appeal without polarising — estate agents often recommend it for this reason.

Shared Strengths

Both plum and grey slate chippings share these practical advantages:

• Angular shape interlocks and stays put — no raking needed
• Won't need replacing once laid (unlike rounded pebbles that migrate)
• Effective weed-suppressing mulch over membrane
• Fish-friendly and safe for garden ponds
• Free-draining and SuDS-compliant

For a full comparison with rounded alternatives, see our Scottish Pebbles vs Welsh Slate guide.

The installation process is identical for plum and grey — the colour is purely an aesthetic decision, not a practical one.

Step-by-Step

• Clear the area and excavate 50–70 mm of topsoil
• Compact the sub-base with a hand tamper or plate compactor
• Lay heavy-duty woven landscape membrane (avoid cheap non-woven types — they degrade quickly in UV). Overlap sheets by 150 mm minimum
• Fix firm edging — metal lawn edging, treated timber, or stone kerbs — to contain the aggregate
• Tip slate onto the membrane and spread to 40–50 mm depth using a landscaping rake

Slate chippings interlock naturally thanks to their flat, angular profile, so you can get away with 40 mm depth where rounded pebbles would need 50 mm. This means slightly less material per square metre — one of the reasons slate is cost-effective for larger areas.

Maintenance: Essentially zero. An annual blow-over with a leaf blower clears fallen leaves. Jet-wash every 2–3 years if algae develops in shaded areas. Unlike rounded pebbles, slate doesn't shift or migrate, so you'll rarely need to rake or top up.

For the full step-by-step with depth guides and edging details, read our how to lay decorative stones guide.