The type of growing medium an orchid needs will depend on what type of orchid it is.
Most tropical orchids are epiphytes, which means they grow in the air rather than in soil. Their roots have a layer of white cells, called a velamen, that protects them from losing moisture while effectively absorbing water from the surrounding environment.
Terrestrial orchids, on the other hand, do grow in soil.
No matter what medium the orchid uses, it has to have good air circulation and should be well-draining. It should also have places that the orchid’s roots can properly cling to.
The most common growing media for orchids are one or a combination of fir bark, sphagnum moss, perlite, charcoal, coconut husk chunks or lava rock.
Of all the media, fir bark nuggets are the most widely used.
In this article, we will dive into what makes for a good orchid growing medium and what the different types of growing media are.
What are the different types of orchid potting media?
Fir bark nuggets
As we mentioned, fir bark is the most popular choice of orchid potting medium. This is probably because it is very affordable and does a great job as a potting medium.
It provides both good air circulation and good drainage, but as a consequence does not hold moisture very well, so you may need to water your orchid more frequently than if you were using other media. You will need to really soak the fir bark when watering the orchid.
You can get fir bark nuggets in small, medium or large sizes. Your choice of nugget size will also depend on the size of your orchid. If the roots are thin and fine, they will work best with small fir bark nuggets.
Because fir bark is an organic medium, you may need to replace it once a year because it will decompose quite quickly.
Sphagnum moss is another popular choice among orchid growers. It provides great air circulation while retaining quite a lot of moisture, so it is a great choice for orchids that like more water than most.
The New Zealand variety of sphagnum moss is considered to be the best quality of all the different types available on the market.
One of the biggest downsides of using sphagnum moss is that it degrades faster than other media and tends to compress over time, affecting the airflow. You will need to repot the orchid once the medium starts to compress. One way to impede compression is by adding some inorganic materials, such as perlite, that do not get compressed.
Sphagnum moss is often used alongside other materials because of how well it retains moisture. It can be added as a top layer so that the medium underneath does not dry out as quickly.
Just like sphagnum moss, coconut husk holds onto moisture quite well. It is a good choice for orchids that need more water than most, or for orchids that are grown in dry places.
Coconut husk chunks are lightweight and allow air to flow freely around the roots of the orchids.
Make sure you rinse the husks in water before use, to remove any salt residue.
Because it retains water so well, you may need to add some clay pebbles to the bottom of the pot for extra drainage.
Charcoal is an organic medium but compared to most, it lasts much longer. Keep in mind that it does not keep the water well, so it is best in places with high humidity.
Charcoal as a growing medium is sold in different chunk sizes, ranging from fine to large. Your choice of size will depend on the size of your orchid.
Charcoal is said to eliminate odors, filter impurities, and help with the pH levels around the plant’s roots.
Lava rocks are also sold in different sizes for use as a growing medium. You should consider their ability to retain moisture when choosing a size: the bigger the rocks, the less moisture they are able to hold.
This is a fast-draining medium that does not rot or decompose, but it can also be quite heavy.
Avoid using lava rocks if you live in a place that has a cold climate because the rocks have a cooling effect and the lowered temperature may negatively affect your orchids.
Inorganic growing media
Perlite is one of the most popular inorganic growing media. It looks like small sugar granules, retains water well, and is lightweight. Perlite does not decompose or compress, which is why it is often added to organic media. It retains water so well that it should not be used alone.
Clay pebbles, or leca, and clay granules, or seramis, are also inorganic materials that can be used as growing media; they also do not compress or decompose.
Unlike perlite, they do not retain water that well, but they do provide great air circulation and good drainage. They are both often used at the bottom of the orchid potting medium to improve drainage.
What makes a good growing medium for orchids?
In their natural habitat, orchids find the right growing conditions, which include humidity, light, temperature, air circulation, drainage, and adequate nutrients.
Ideally, orchids should be in a place where humidity levels are between 60 to 80%, so the growing medium should be able to retain moisture to some extent.
Temperatures should not be lower than 15 degrees Fahrenheit, and the growing medium should be able to protect the plant.
The orchid should be able to attach to, or be supported by, the growing medium. The medium should also not be too dense or compact so that light can still penetrate it to reach the roots.
Recreate these living conditions in your pot with your potting medium, and your orchid should have no problem growing.
The most common growing media for orchids are fir bark, sphagnum moss, perlite, charcoal, coconut husk chunks or lava rock. Some of these can be used alone, while others have to be combined with other growing media to make a customized potting mix that is best for your orchid.
The kind of medium you choose will depend on the climate where you live, the size of the orchid you are growing, the humidity, the temperature and the amount of water your orchid is going to need.
If you are still unsure as to which type of medium your orchid needs, ask at the local store and they might be able to recommend a potting mix for you.
Image: istockphoto.com / Ekaterina Fedulyeva