When growing Rhododendron, it is essential to keep in mind that these are the plants coming from poor forest soil with enough humus, and they occur in areas rich in rainfall. Rhododendrons demand permeable, airy and sour soil. PH value suitable for Rhododendrons should be in range of 4,5-5,5. Therefore, the very preparation of growth substrate is very important and cannot be underestimated.
The most suitable soil for Rhododendron growing is rough and fibrous peat. It meets all the requirements, it is airy, and takes up and holds up water very well. Its pH value is very low. Very suitable is also pine litter, containing largely decayed coniferous needles, with characteristics similar to peat. Its pH value is virtually ideal, between 4,5-5,0. Leaf mould is not very suitable for Rhododendron growing. It can be only used as an additive for filling, but maximum one third of the total volume.
Pine bark has great loosening ability and also holds up moisture very well, so it is suitable as an addition for a soil mixture. Substrate is often enriched with a mixture of sawdust particle or wooden chips that also hold up moisture very well and they can plough rougher soils, too. To increase permeability, sand or perlite can be used as well.
In decorative gardens, we can often encounter Rhododendrons in the plastic containers. This substrate usually consists of peat and ground pine bark, and it is not rich in nutriments. For that reason slowly soluble fertilizers are added. Rhododendrons get additional fertilizers also during growing season. When planting, we recommend knock of the roots gently, pour them in the water and prepare sufficiently big hole that will be filled with above mentioned substrate forms. Or, you can purchase ready-made substrate for Rhododendrons.