The properties of material that touches the root of the orchid influences the health of your plant on the long term. In this article, we review key properties of potting media.
This article is intended
as a guide if the potting media of your choice is not covered in our other post that describes the most popular potting media so with the below information you can decide on the application of the material;
to provide more information on potting media in general.
What is potting media and why is it used?
Potting media stabilizes the plant so it will not get damaged as a result if the roots were moving freely inside the flower pot. Orchids do not move around in their natural habitat and so even re-potting, the change of material around their roots can upset the plant.
The right potting media reduces the frequency of re-potting as well as the time spent with watering while also provides the plant with optimal air circulation, ventilation around the roots therefore it promotes growth and reduces likelihood of chemical imbalance, mold growth and bacterial infections. Choosing the right potting media is therefore key to growing healthy orchids indoors.
Based on what criteria should we choose potting mix?
Potting mix, the material has the following, four key parameters:
water retention;
size of pot and potting media;
the time until it decomposes (organic vs. inorganic media);
pH level
Water retention: over-watering often causes root rot and only some plants can recover from that. Even a dehydrated phalaenopsis needs air around its roots for most of the time - this is true for the majority of phalaenosis plants. Odontoglossum orchids, on the other hand like wet environment more than phalaenopsis as well as cattleya so the type of orchid should have an impact on the choice of potting media. The humidity of your home and also your free time you can spare watering the orchids will also determine which potting media to use from the perspective of water retention. Beginner orchid growers usually start with either bark or a mix of bark and moss. These will be reviewed later in this article to help avoiding common mistakes of working with bark and moss as well as other popular potting media.
Lifetime of potting mixes vary. Organic potting media like bark starts to decompose and transforms into a coffee ground sort of texture, peat in about a year or so. As we water the orchid, more and more of the media are going to fall apart in the pot. The sand-like remains of the bark means there is less air the roots have access to and eventually these roots will suffocate. The air pockets around the orchid roots are destroyed by fine grain of decomposed media so the roots sooner or later start to rot. At the same time, bad bacteria start spreading in the pot and infect other healthy roots. Orchids need their roots to hydrate themselves. Inorganic potting mixes (e.g. clay pebbles, glass beads) do not decompose that fast and keep their shape for years; however, when we compare bark with clay, we can conclude that clay would require much additional work as maintenance (see more details on clay and keeping its PH level optimal below).
Size of pot: choose a pot relative to the size of the orchid and make sure the pot is not much bigger than the root system because having an over-sized pot would promote root rot. The less potting media is in the pot, the more ventilation the orchid would get because its roots will be closer to the ventilation and drainage holes on the pot this way. If extra ventilation holes are provided on the side of the pot then ventilation is usually more intense around the edges of the flower pot and that area dries out more quickly compared to the middle area of the pot.
Size of potting media is usually determined by the family the orchid belongs to and at times also the size of the roots. Odontoglossum orchids, for example have relatively thin roots compared to phalaenopsis. For example, if we have some excess bark at home and would like to use it up for the next re-potting of an orchid keep in mind the type of the plant. For odontoglossum orchids we will need smaller bark than the bark we use for a mature phalaenopsis otherwise the plant will not be able to stand in the pot. The tiny bark can fit in between smaller holes among thin roots which can stabilize the odontoglossum better than bigger pieces of bark.
The pH level refers to certain chemical state, the level of acidity of the potting media. While fertilizers certainly influence the pH in the pot, the potting media itself has a pH value that changes over time. For example, as bark decomposes it becomes more and more acidic and clay media has a relatively high pH value to begin with. If you are not using clay or volcanic stones in your pot then as long as you follow re-potting and fertilizer guidelines it is unlikely that you will have pH issues. Orchids prefer natural to slightly acidic pH level in their pot depending on their type (e.g. phalaenopsis likes slightly acidic conditions). If you are planning to use clay media, it is important to control its pH over time because if pH is too low or too high the orchid will not be able to absorb minerals from fertilizer and so its health will suffer over time. More information about pH can be found on Wikipedia.
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