Rock Garden or Scree Garden?
When considering a rock garden, and obviously this involves sizeable rocks – we can always use something rather more manageable – gravel, as used in making a scree garden. Scree refers to the mass accumulation of broken rock and small stones that naturally occurs at the foot of a rock or cliff face. It is the result of the natural degradation of the rock by weathering. The uppermost strata is dry and sunbaked, but the substrata is cool and moist because of the water run-off flowing from the mountainside and into the scree.
In the garden you can easily combine a scree with a rock garden in an imitation of nature, with one end of the rock garden seemingly disintegrating into a gravel carpet. But if you have no room or inclination for a rock garden, you can simply have a scree, perhaps as an apron around the house foundations, in which to grow alpine treasures or simple rock plants.
As with all forms of rock gardens, perfectis vital, as is an open site away from overhanging trees. Mark out the shape of the scree garden just as you would any garden bed, except bear in mind that you are mimicking nature and in the mountains a scree fans outwards from the foot of the rocks. If you are making a scree garden in isolation, try to achieve a shape that looks like a spreading puddle of gravel.
To make a scree garden you must first remove the topsoil to a depth of 45 cm/18 in. This may take you into the subsoil, in which case prick it over with a garden fork, but do not dig it over. Backfill with 15 cm/6 in of clean rubble and compact this firmly into the bottom of the garden site. Finally, cover the rubble with a 5 cm/2 in layer of gravel and coarse sand.
To emulate the action of water running below the plants, you can install a drip hose irrigation system. During a drought this will help to ensure the plants remain watered at their roots, as overhead watering can be detrimental to many rock plants.
A drip hose system is easy to use. First, lay the hose over the gravel and sand, spacing it out according to the manufacturer’s recommendations. Then cover the area with 2.5 cm/I in layer of compost made from fine gravel, clean loam and peat in a ratio of 3:1:1. The hose should also be covered.
Finally, spread an even gravel mulch, up to 2.5 cm/1 in thick, over the entire area. You can dot the scree with some interestingly shaped large boulders or with chunks of tufa rock, which have been planted up – there are many rock and alpine plants to choose from.