Rock Garden Ideas: Alpine Plants, Stone and Drainage

Getting it right

Use one type of stone, ideally from a local quarry, and bed each piece about a third into the ground with the layers running the same way; mixed rock types are the giveaway of an amateur rock garden. Make the planting mix roughly half sharp grit and half topsoil, then top it with about 2 inches (5 cm) of chips of the same stone. Plant into the gravel rather than onto it, and keep the crown of every alpine sitting slightly high so water always drains away from it.

How to plan it

Pick the spot: full sun, good air movement and, ideally, a gentle slope that already drains. A south- or west-facing bank is perfect. Avoid the low point of the yard and the shade of trees; falling leaves smother small alpines and hold moisture against their crowns.

Build it as an outcrop, not a pile. Set the largest stones first at the base, tilted back into the slope, then step smaller stones up and back so they look like one layer of rock coming to the surface. Fill the pockets between them with the gritty mix and plant into those pockets, with mat-forming plants such as creeping thyme and creeping phlox where they can spill over a stone.

Upkeep is mostly weeding for the first two years, until the plants knit together, plus topping up the stone chips. Trim rock cress, candytuft and creeping phlox lightly after flowering to keep them tight, and pull any seedling that crowds a slower plant.

Plants that work

Botanical names come first so you can order the right plant anywhere. Heights are for mature plants in the ground.
Plant	Type	Light	Water	Height	Hardy to
Hens and chicksSempervivum tectorum	Succulent · Evergreen	Full sun	Low	3–6 in (8–15 cm)	−22 °F / −30 °C
Goldmoss stonecropSedum acre	Succulent · Evergreen	Full sun	Low	2–4 in (5–10 cm)	−22 °F / −30 °C
White stonecropSedum album	Succulent · Evergreen	Full sun	Low	2–6 in (5–15 cm)	−22 °F / −30 °C
Mossy saxifrageSaxifraga × arendsii	Perennial · Evergreen	Partial shade	Moderate	4–8 in (10–20 cm)	−13 °F / −25 °C
Rock cressAubrieta deltoidea	Perennial · Semi-evergreen	Full sun	Low	4–6 in (10–15 cm)	−13 °F / −25 °C
Maiden pinkDianthus deltoides	Perennial · Semi-evergreen	Full sun	Low	6–10 in (15–25 cm)	−22 °F / −30 °C
Sea thriftArmeria maritima	Perennial · Evergreen	Full sun	Low	6–10 in (15–25 cm)	−22 °F / −30 °C
Creeping thymeThymus serpyllum	Groundcover · Evergreen	Full sun	Low	2–4 in (5–10 cm)	−22 °F / −30 °C
Dalmatian bellflowerCampanula portenschlagiana	Perennial · Semi-evergreen	Partial shade	Low	4–8 in (10–20 cm)	−13 °F / −25 °C
Evergreen candytuftIberis sempervirens	Perennial · Evergreen	Full sun	Low	8–12 in (20–30 cm)	−13 °F / −25 °C
Creeping phloxPhlox subulata	Groundcover · Semi-evergreen	Full sun	Low	4–6 in (10–15 cm)	−22 °F / −30 °C
Alpine asterAster alpinus	Perennial · Deciduous	Full sun	Low	6–10 in (15–25 cm)	−31 °F / −35 °C
Mugo pinePinus mugo	Conifer · Evergreen	Full sun	Low	3–10 ft (1–3 m)	−40 °F / −40 °C
Blue fescueFestuca glauca	Grass · Evergreen	Full sun	Low	8–12 in (20–30 cm)	−22 °F / −30 °C

Surfaces and materials

Boulders
Crushed granite
Dry-stacked stone wall
Stepping stones
Gravel mulch
Slate chips

Works well when

The soil is thin and poor
The soil is sandy and free-draining
The ground slopes steeply
It gets sun for most of the day
You want low maintenance

Think twice when

The ground stays wet after rain
It is shaded for most of the day
The soil is heavy clay

Common questions

What's the difference between a rock garden and rock landscaping?

Rock landscaping usually means gravel or river rock used instead of lawn or mulch. A rock garden is a planted feature: stone and grit built up to grow small alpine plants that need sharp drainage. You can combine both, with a rock garden as the focal point in a gravel yard.

What rocks should I use?

One type of local stone in a range of sizes, with a few pieces big enough to need two people to move. Local stone matches its surroundings and costs less to deliver; mixing sandstone, granite and lava rock is what makes a rock garden look artificial.

Do rock gardens need landscape fabric?

Not under the planting. Fabric stops plants rooting and spreading, and soil builds up on top of it anyway. Clear perennial weeds thoroughly before you build, and rely on a deep layer of stone chips to suppress new ones.

Can I build a rock garden on clay soil?

Yes, but build up rather than down. Raise the whole feature 12 inches (30 cm) or more above the clay with a gritty mix, so water drains out of the root zone instead of sitting in it.