Above all, rock garden soil should have good drainage properties, as most typical rock garden plants prefer dry locations. On the other hand, commercial compost with its high nutrient content is unsuitable, since the rock garden plants, which are used to poor soil, only need low nutrient concentrations.
Good drainage is particularly important in a rock garden
Mix the rock garden soil yourself - this is how it works
Of course, it is ideal to mix the right soil yourself from existing, weed-free topsoil and fine rock chippings or gravel. With "normal" rock garden plants, a rock content of approx. 30 percent should be sufficient. In the case of plants that are more difficult to care for, however, the proportion can rise to 50 to 80 percent, depending on the species. Always use the same type of rock for the soil mixture as you chose for the "boulders". If the soil is very heavy or loamy, you should also mix in gravel and grit (€46.95) in the deeper layers of the earth to ensure adequate drainage.
Suitable soil for lime-loving and lime-fleeing plants
When selecting the rock - regardless of whether it is boulders or gravel - you have to pay attention to whether it is limestone or silicate rock. After all, not every rock garden plant grows on every stone. Lime-loving plants need limestone, while they would inevitably die on silicate rocks such as granite or slate. Lime-fleeing species, on the other hand, must not come into contact with lime and are therefore better off in silicate mixtures.
Soil for lime-loving plants
If you mix soil for lime-loving plants, do without peat (which acidifies the soil) or bark mulch (same effect) and instead use between 10 and 15 percent high-quality bark humus or garden compost that is several years old. High-quality clay potting soil from specialist retailers is also very suitable.
Soil for calcareous plants
Plants that flee limescale, on the other hand, need peaty soil with a low pH value. Here it is best to mix 30 percent topsoil or lawn soil with 20 percent bark humus, 50 percent sod peat, gravel and chippings (on a silicate basis! Granite is suitable, for example) and around one kilogram of horn shavings (€32.93) per cubic meter. Instead of this mixture, you can also simply mix ready bog bed soil with fine rock.
Mulch the soil surface with crushed stone
It has proven to be best if, after planting, an approx. one centimeter thick layer of mulch from the rock chippings mixed into the soil is applied to the substrate. The surface then dries faster and the plants feel more comfortable. Incidentally, the soil mixtures described above have also proven themselves for planting in troughs, bowls, pots, balcony boxes (€109.00) etc.
tips
If a drainage layer has to be introduced into the ground, lime-free rubble such as crushed bricks or broken roof tiles is also suitable.