The substrate – the basis of a successful culture

culture methods

  • Bare root – here the plants are usually tied to a wire and cultivated without substrate or rootstock, all roots are exposed. In summer, it must be watered daily so that the plants do not dry out. The method is well suited for epiphytic orchids that require a lot of air at the roots, such as all species and hybrids of the genus Vanda.
  • Tied on – in this method, the plants are tied on solid supports, such as pieces of bark. The roots grow along the substrate and hold on to it. To moisturize them a little more evenly, you can cover them with moss or other water-holding plant material, as needed.

This culture is particularly recommended for small orchids that grow in a humid environment, e.g. B. a showcase to be maintained. But there are also species that thrive on the windowsill. See the articles on Seidenfadenia mitrataand Chiloschista parishii in our category “Orchid of the week”.

  • Potted – this is the most common type of culture and is suitable for most species and hybrids of orchids. The roots are more or less surrounded by plant material and are therefore supplied with moisture for longer. Plants that like it really wet also feel comfortable in pots, such as most Phragmipediums, including Phragmipedium besseae, also featured as “Orchid of the Week.”

Organic, mineral or artificial?

Once you have decided on the culture method, you have to think about what material the substrate or pad should be made of. A distinction is made between organic (plant parts), mineral (stones and clay) and artificial substances (polystyrene, rock wool). The latter are usually only used as additives.

Organic botanicals

are renewable raw materials and 100 percent biodegradable. Depending on the moisture content, they decompose more or less quickly. On the one hand, nutrients are released through this process, from which the orchid benefits, on the other hand, it has to be repotted more frequently because the substrate becomes compacted, hardly dries and no longer allows air to reach the roots, which can then quickly rot.

Basically, repotting always means stress for a plant and should only be done if it has to be.

  • Bark is ubiquitous in orchid culture – whether as a large piece for tying up orchids or as a fine substrate for potted young plants. Bark is able to store some water and dries quite quickly, depending on the grain – so ideal for all epiphytes whose roots should not be permanently wet. But moisture-loving orchids can also feel comfortable in bark if the watering behavior is adjusted accordingly. In the warm summer months in particular, it has to be watered or dipped more often. Additives are often added to the bark substrate to increase the water storage capacity or to make the planting material more airy. Constant moisture is difficult to achieve with bark. There is always a certain alternation of wetter and drier phases, which meets the needs of many orchids. Uniform moisture is achieved by cultivating with »wet feet«. However, this is not recommended for most orchids.
  • Sphagnum moss is suitable for orchid culture in both dried and living form. It is often used as a base for attached plants. But it is also suitable as a plant material in a pot. Living moss is itself very sensitive to salt and can be used as an indicator for the right water quality in salt-sensitive orchid species. As long as the moss stays nice and green and continues to grow, the water quality is right for sensitive plants. Probably the biggest disadvantage of Sphagnum moss is that it accumulates salts very quickly, which is why it should be repotted annually. Its great advantage is that it can store a lot of water, which is gradually released to the plant. However, it must not dry out, otherwise it becomes unusable as a plant material. It does not matter whether it was originally dried or live Sphagnum moss, constant moisture must be ensured.
  • Coconut fibers and coconut chips – The outer shell of coconuts has also entered the orchid scene in recent years, available as loose fibers and as coarse pieces. Before they can be used as plant material, they have to be rinsed or soaked well several times with clear water in order to flush out the salts they contain. Otherwise sensitive orchid roots would burn very quickly. Coconut fibers and chips can also store a lot of water and do not decompose quite as quickly as pieces of bark. However, similar to Sphagnum moss, they quickly accumulate salts. Regular rinsing of the pot with clear water is therefore also mandatory during culture.
  • Charcoal is only used as an additive, i.e. it is mixed with other plant materials. Since charcoal hardly absorbs any water and is also very light, it loosens the plant material and ensures that the areas inside the pot are a little drier. So-called activated charcoal also has an antibacterial effect and protects the roots from infection if they are injured. BUT: Not all charcoal is activated charcoal. Activated carbon is only produced from plant, animal, mineral or petrochemical substances through complicated processes.

mineral plant substances

The great advantage of mineral substrates is that they do not decompose. Thus, the plants only have to be repotted when the planter has become too small, which is often only the case after many years. Mineral plant substances are particularly suitable for all orchids that love even moisture and do not want to dry out completely. The pot can be permanently placed in a bowl of water. Due to the capillarity of the parts of the plant material, the water is drawn upwards, creating an even moisture content in the pot without the substrate and the roots becoming too wet. The disadvantage of mineral substrates is their temperature. Compared to organic or artificial planting materials, they are significantly cooler. They are therefore not suitable for heat-loving orchid species.

  • Lava granules are very porous, can therefore store a lot of water and are relatively light. Commercially available lava granules usually have a grain size of 2-8 mm, coarser grains are called lava mulch, smaller ones are called lava sand. The granules in particular have become firmly established in orchid culture. Mulch has too low capillarity and therefore remains too dry, lava sand gets too wet. A small disadvantage of lava is that the surface is full of sharp edges. When repotting, you have to be very careful not to damage the fine roots. The advantages are obvious: it stores water well, is relatively light and airy and does not decompose. Red colored lava should not be used under any circumstances, as it is very ferruginous.
  • Akadama or akadama soil is obtained from volcanic ash loam from the Kantō region of Japan and is offered fired (“hard quality”) and unfired (“high quality”). The former, which is also used in bonsai culture, has also proven to be suitable for growing moisture-loving orchids. The pH of Akadama is slightly acidic (between 5 and 6). Like all mineral substrates, it is structurally stable and, thanks to its coarse grain size, offers good aeration for the roots. Akadama is also very suitable as an aggregate in bark mixtures to increase the storage capacity of the substrate.
  • Pumice gravel is rarely used pure in orchid culture, although this is also possible. It ensures optimal ventilation of the roots and has been valued as a “soil conditioner” in horticulture for decades. Pumice rock is closely related to lava, but even more porous and therefore lighter than it. In addition, its surface is less sharp than that of lava.
  • Perlite has also been an integral part of horticulture and orchid culture for many years. It is pH-neutral, very light, structurally stable and stores water very well. It is also mainly used as an additive to make the substrate more airy and lighter. Caution is advised with perlite, which is offered as a building material. This is often covered with silicone or similar and therefore unsuitable for orchid culture.
  • Expanded clay consists of low-calcium clay with fine organic components, which is fired at high temperatures and thus obtains its structural stability. It is a good water reservoir and does not bind any nutrients. The nutrient supply can thus be controlled more precisely. Expanded clay can be used pure or as an additive.

artificial substrates

Probably the biggest disadvantage of artificial substrates is that after use they must be disposed of in the residual waste.

  • Styrofoam or also called polystyrene is extremely light and hardly absorbs water. This makes it very suitable as a drainage layer in the bottom of the pot or for loosening up the substrate. Similar to charcoal, it creates slightly drier areas within the planter and provides good ventilation for the roots. Even though it is resistant to water, Styrofoam rots when exposed to UV light and is therefore not structurally stable in transparent pots.
  • Rock wool cubes are resistant to mold, rot and vermin. They can absorb, store and slowly release an enormous amount of water. Especially for very moisture-loving orchids, they can be used both pure and as an additive. Its fibrous structure with large spaces ensures good aeration of the roots. Over time, however, the components compact and it has to be repotted regularly – after two years at the latest.