Mound and firm the soil in the area where you want to establish your crevice garden. Remember that the height of the peak should be at least 60 centimetres, and the slopes-so water will run off-between 20° and 45°. Slope one side to create a gradual, or dominant, plane; the other side should be steeper. The overall effect is a wedge of cake. Firm soil in place.
Create the dominant side first, which is meant to resemble a mountainous slope. (Figures 1 and 2). Lay the stones flat: start at the bottom and work toward the top of the ridge, laying stones 5 or so centimetres apart; place a few 10 to 15 centimetres apart. Leave ends and the top of the slope bare so you can incorporate them into the other side. Abut bottom and top edges against each other to hold stones in place. As you're working, if you lay a stone and aren't happy with its appearance or how it fits with its neighbours, turn it over to see if you like that effect better.
On the other, steeper side of the ridge, you're creating an outcrop or ledge of rock by digging the stones into the mound as if they were stacked and tilted inward on a steep incline. The angle of these rocks should be the same as the angle of the rocks on the dominant side (see illustration). Start from the top of the ridge and from the ends where the two faces meet, so you have an immediate plane of reference; work across in rows. Use a spade or trowel to dig depressions in the soil where you'll insert approximately two-thirds of each stone (Figure 3).
Fill soil in the pockets, as necessary, and plant (Figure 4). Add a mulch of fine gravel or tufa-depending on the type of stones you used-to blend everything together.
MATERIALS FOR A GARDEN ROUGHLY THREE BY THREE METERS
• Two cubic metres of a sandy topsoil. It's easy to form into a mound, and retains a suitable amount of moisture for alpine plants.
• The most popular types of stone used for crevice gardens are limestone and tufa. Or use granite if it's indigenous to your area-whatever type of stone you use should look natural, and use the same type of rock throughout. Choose irregularly shaped, different-sized stones, 8- to 10-centimetres thick that have at least one flat side. Select stones you can comfortably lift. You'll need between 500 and 1000 kilograms of limestone or 175 to 350 kilograms of tufa.
• Approximately 50 kilograms of 10-millimetre gravel or 25 kilograms of tufa chips.
• Plants (see next page)