How deep should landscape rock be?

Depth matters, but the two things that actually decide whether a rock bed lasts are underneath it: the fabric and the edge.

Depth by use

Where	Depth
Decorative bed, no foot traffic	5–7 cm
Mow strip / foundation band	6–8 cm
Walkway or path	8–10 cm
Around trees / large plants	5 cm, kept off the trunk

Deeper than about 10 cm just wastes rock — and on beds with plants it can smother roots.

Estimating how much you need

Rock is sold by the tonne or the cubic yard. Rough rule for the Calgary area:

• 1 cubic yard covers about 100 sq ft at 7 cm deep.
• 1 cubic yard of most landscape rock weighs roughly 1.3–1.5 tonnes.
• So a 300 sq ft bed at 7 cm ≈ 3 cubic yards ≈ 4–4.5 tonnes.

Add ~10% for uneven ground and settling.

What goes under the rock

• Commercial non-woven filter fabric — overlapped 15 cm and pinned. Not the cheap woven cloth from a big-box store.
• A compacted, drained base — the bed is excavated to depth, not built up on the lawn.
• Steel or heavy aluminum edging, staked deep — this is what keeps rock and lawn separate for good.

Get those right and 6 cm of rock lasts 20 years. Get them wrong and 10 cm of rock is in your lawn by year three.

FAQ

What size of rock is best?

20–40 mm for general beds — big enough not to track, small enough to look tidy. Larger cobble for accent and drainage areas.

Do I need edging if I have fabric?

Yes. Fabric stops weeds; edging stops the rock migrating and the grass creeping in. They do different jobs.

Can I just top up an existing bed instead of starting over?

If the fabric and edging underneath are still doing their job, yes — a thin top-up refreshes the colour and depth for a fraction of a rebuild. If rock has already migrated into the lawn or weeds are through the fabric, topping up just buries the problem; that bed needs to come out and be rebuilt properly.