There is no one answer to the type of potting mix which can be used for all orchid genera as there are many things to be taken into consideration.
Different orchid genera require different types of potting mixes.
Orchids do not like wet soggy roots. This is often the main reason for orchid death.
Orchid mixes require space between the particles to allow air to circulate and water to drain. The mix needs to absorb and hold water as well as be able to dry out.
A general rule is the larger the orchid; the larger the pot and the larger the mix used. A small orchid generally requires smaller mix.
Do not allow plants to sit directly on the ground as worms can enter the mix and break it down creating a mud like mix.
Some orchids don’t thrive in any mix at all. Mounts are then used. This is where orchids are attached to board, cork, man fern etc.
EXAMPLES OF MIXES AVAILABLE IN TASMANIA
Bark supplied by the Orchid Society
Excellent for Cymbidiums and larger orchids. Ask at the society as to where to obtain this. The society’s monthly newsletter also contains contact details for bark purchase.
Mainland bark purchased through the Society
This comes in two sizes suitable for either smaller plants such as Masdevallia and Sarcochilus or larger orchids such as Cymbidiums. This bark is ordered once a year by the society. A notification is placed in our newsletter at midyear for members who wish to place an order.
Man Fern mulch
This can be purchased commercially at around $10.00. It is made from the trunk of man ferns. This mix is used on its own or mixed with the above bark, pebbles or coarse sand to help with drainage.
Excellent for smaller plants and sick plants, but it may be difficult to obtain.
Inorganic materials such as perlite, pebbles, coarse sand can be used to open up the mix allowing the mix to drain and to create air spaces.