Initially the first orchid enthusiasts kept their orchids in soil, and naturally they failed to grow epiphyte and lithophyte species – soil is not suited for these species, only terrestrial species such as Calanthe proceeded to grow in this heavy substrate. Eventually, some started using Osmunda fern as substrate. Finally they succeeded, and this was the Golden Age for orchid growing (many hybrids were created in Osmunda era), but there was one problem. Osmunda is a rare species, and excessive orchid growing drove Osmunda to near extinction. After this, orchid enthusiasts started to experiment with organic components to make something, effectively mimicking Osmunda. And they have found these principal components – pine bark, sphagnum moss, charcoal and cocoa fiber and chips.
And this founding started the new era of orchid growing. Varying the percentage of these components you can make more open and dry substrate, suited for more succulent and xerophytic species just like some Cattleya – medium pine bark without any sphagnum and other components is OK, but by adding sphagnum you can make a substrate, suited for orchids from more humid environments, such as Stanhopea and Coelogyne species. You should vary these components, considering which species you grow and which watering technique you use. You should know that if substrate remains wet for entire week or even longer, it is not OK, so if you’re growing epiphyte orchids, you should add more bark and make more ventilation holes.
These components are also suited for terrestrial species such as Jewel orchids, Cymbidiums and Paphiopedilum – you should only use more fine bark and sphagnum, and for Jewell Orchids you can add some soil, some peat moss, perlite and leaf debris to mimic their home environment. When we talk about Paphiopedilum potting mixture, you should know that there are some epiphytic species such as Paphiopedilum rothshildiana, which require more open substrates with more bark, and there are more terrestrial species, which require more humid substrates. And there is so called calcicolous Paphiopedilums, such as Paphiopedilum sanderianum. Their name calcicolous means, that they require additional calcium supplementation and substrate with slightly base pH (unlike non-calcicolous species, which require slightly acidic substrate). For these Paphiopedilum species you should add some limestone or oyster shells to provide both calcium supplementation and suitable pH. Some orchid enthusiasts use egg shells for this reason, but it is too fine and alters water capacity of the substrate, instead using limestone is better.
Some lithophytic species such as rupicolous Laelia and some Bifrenaria species can be grown in lava-rock based substrates – you can also use pure lava rock to grow them, or some ceramsite. Lava rock is open and well-aerated and well suited for lithophytes, and unlike bark or other organic substrates it is not breaking up with time.
Nowadays, some more modern substrate components were discovered, such as Epiweb or Polystyrene Chips and other plastics-based substrates. They have open, well draining and have good water capacity, they are also quite inexpensive and there one very good thing about them. They are not breaking down by microorganisms, so they are not changing their properties over time (bark while breaking down becomes soggy and holds a lot of water, so old substrate becomes less airy and you should repot into fresh one, if you do not want to rot your orchids root in anaerobic conditions). You can use both pure Epiweb or Polystyrene Chips, or as components for substrates (but do not mix them with peat moss), because Epiweb is excellent for more dry-loving orchids such as Cattleyas, if you growing more humid-loving species such as Paphiopedilums or Bulbophyllums you should add some sphagnum to correct water capacity of substrate. Also, you should know that when you use plastics-based substrates for orchids, you should feed orchids better because of the lack of nutritional substances in such substrates.
Finally, there are numerous orchid potting mixtures on the market nowadays, so if you want, you don’t need to prepare the mixtures for your orchids yourself.
Some orchid substrates for sale from Amazon.com
Orchiata Orchid Substrate (1 Quart)
Sun Bulb Better Gro 4-Quart Orchid Bark
Sun Bulb Company Inc
Orchid Potting Mix — Medium Orchid Bark with Charcoal & Sponge Rock. 1/4 Cubic Foot Bag.
Jim’s Orchid Supplies