When choosing a potting mix, keep in mind whether your orchid is epiphytic (they grow on branches and trunks of trees) or terrestrial (those that grow in the soil in the wild) as this will have an impact on what media to use.
Other things to keep in mind are:
- The draining ability of the media; water should be able to flow freely with enough retained for storing and distributing the necessary amount of humidity, without becoming waterlogged,
- Air must be able to circulate around the roots,
- The media should withstand decomposition as long as possible,
- And must be able to support the plant.
Many of the orchids we commonly grow are epiphytic in the wild. High up on the trees in the rainforest, they cling to branches without much around their roots.
Rain washes down the branches over the orchid roots and continues to drain away. So it is logical to use open, free-draining compost.
The type of compost that most resembles these natural growing conditions is one made up of bark chippings. Epiphytic orchids can be grown in a wide range of media, and you will find most combinations of barks, tree-fern fibre, perlite, sphagnum moss, peat moss, cork bark popular.
Terrestrial orchids should be grown in a medium that contains 40% organic matter, holds water, yet is well drained, contains some nutrients, and most importantly be able to support the plant.
Inorganic potting mixes are commonly used; this requires more attention and structure to the feeding and watering as all nutrients have to be given via the water.
Some popular potting media include:
Peat moss or a peat substitution will help to prevent drying out, which is good for those orchids that like a bit of moistness, such as terrestrial Paphiopedilum and Pleione.
Peat moss is made up of decomposed and fermented sphagnum moss which retains moisture easily and combines well. The down side is it makes the compost too heavy and restricts circulation. It can accumulate and retain salts, which may cause excess salinity damage.
Sphagnum moss is a live moss that grows in wet places. It holds water well but the downside is it goes off relatively quickly, especially after contact with fertilizers.
Chunks of coconut fibre are similar to bark in that it holds some moisture whilst draining freely.
Coconut husks; the covering outside of the coconut shell, is seen as a replacement for bark. Husks are relatively cheap and easy to find. It is generally more consistent in shape then bark, so it promotes better air flow throughout the roots.
The husks are also longer lasting then bark, and hold a lot more water. Though, with a fairly high salt content, it is a good idea to soak and rinse this media a few times before use.
Tree fern is long lasting, well aerated, and highly resistant to decomposition. While it permits good aeration of roots, tree fern possess great supportive qualities. It can be used in shredded form as part of a mix or as a whole to grow epiphytic plants on.
Ground bark can be used alone or in mixes, with fir bark being the most popular.
Charcoal is an excellent choice, provided is has not been treated for use in barbecues. Keep in mind that it does not hold much water.
Perlite is expanded volcanic glass. It is lightweight and promotes good aeration and drainage. It is common to add perlite into a peat and bark mix to help with drainage.
Having said all that, you will find that a 50/50 mix of peat and perlite works well for most orchids.
I Hope You Enjoyed today’s Orchid Tips!