Most cultivated trees and shrubs are neutral to slightly acidic (pH 6,5-7,0). Many woody plants are quite tolerant to soil pH, however, the plants, the cultivation of which is possible only in soil with a certain pH. Yes, e.g. cultivation of rhododendrons (Rhododendron), Azalii (Azalea) and heather (Calluna) is only possible in an acidic medium with a pH value within the limits 4,1-5,0. In addition, these plants require large amounts of organic material around the roots and a significant amount of soil moisture. There are very few natural habitats with such properties, therefore, the planting places for these plants should be specially prepared. For the cultivation of these plants, places partially shaded and sheltered from strong winds are selected. However, it should be remembered, that the selection of such places in the vicinity of large trees with a shallow root system is inappropriate, especially in soils with low moisture content. This is because the lack of a sufficient amount of water in the substrate may be a significant obstacle in the development of these plants.
In order to create the right soil conditions for the cultivation of azaleas and rhododendrons, it is most often necessary to remove the local soil to a depth 30 cm and replace it with a layer of high peat or material with similar properties and acid reaction, such as decomposed oak leaves or forest litter with a predominance of pine needles.
Preparation of a stand for rhododendrons on an alkaline clay substrate 1 - clay substrate, 2 - 10-15 cm layer of sand with high peat in a volumetric ratio 5 : 1, 3 — 30 cm high peat or similar material, 4 - drainage pipe.
If, for example, there is an alkaline clay subsoil below the stripped earth layer, they must be removed to the depth 40-50 cm and replaced with loose sandy soil with a high content of humus and acidic reaction. This will help to maintain an acidic reaction in the upper layer, and at the same time creates a layer that drains excess water. If the site is located in a recess, on an impermeable base, it is necessary to ensure the outflow of excess water by installing appropriate filters.