Planting a Rock Garden
Once the rock garden has been built, or an existing one cleaned of perennial weeds such as couch grass, it's time to plan out your planting scheme. Set out your plants in different positions whilst they are still in their pots to give you an idea of how they will look. Make adjustments as needed, taking into account the eventual height and spread of the plants - especially for those species with vigorous and rapid growth.
Planting areas should be dug out and filled with 10 cm (4 in) of small rubble, crocks or stones, and an appropriate soil medium. Before you start to plant, water all the plants thoroughly and allow them to drain. Slide each plant carefully out of its pot and tease some of the roots out to encourage them to spread. Remove any moss and weeds from the compost and check the roots and top-growth for pests and diseases.
Using a trowel or hand fork, make a planting hole large enough to accommodate the root ball. Ease the plant into the hole so that it sits with the collar slightly above the surface of the compost, then fill in with compost. Firm around the plant gently, making sure that there are no air pockets between the root ball and the compost, and then label. Add a top-dressing of grit or gravel.
If plants are to be planted into a crevice, dig out a hole slightly larger than the root ball, and push the roots to the back of the crevice. Fill in with soil, tamping it in with a narrow implement. If the crevice is bigger than the plant, you may find that you need to add in some pieces of stone to wedge the plant in.
Whilst alpines and rock garden plants may be planted at any time of the year, it is usually best to do so in spring to early summer. At this time, the plants are growing actively and will establish quickly, and you will avoid planting in very wet, dry, freezing or hot conditions.
When all the plants are in place, check that the whole area is properly top-dressed and then water them in thoroughly. Keep the plants moist until they are well established and are starting to make new growth; this may require weekly watering until the roots have penetrated the surrounding compost. Crevice plants may be kept moist by using a water spray.
Once the plants are established, there should be no need to water them except during a drought. You may need to re-firm any plants that may have worked loose from time-to time, adding new compost if necessary.