I start with regular potting mix and stir in some cactus mix, so I have approximately a 2 parts to 1 part mixture. Then I mix in a little perlite, maybe a good handful or two.
One thing to keep in mind, that will
make a difference when you decide on your soil mixture, is your preferred method of watering. I water rarely, but very deeply, forcing all of the air out of the soil. My holiday cacti are watered maybe
once every 3 weeks. (I'm a rather inattentive gardener, I'm afraid.
) While I want my potting mixture to drain rapidly, I also like to include the perlite to help retain a little moisture, just in case I suddenly realize I haven't watered the plants for more than a month. (
) If you are a person who is careful to water your epiphytes more often, say every week or two, then they might be happier without
the added perlite.
I haven't grown orchids, but it stands to reason that the bark mix designed for them could be a good addition to a mix for other epiphytes. The difference I see in the way the plants grow in the trees is that plants like the hoya and the holiday cacti tend to grow in spots where debris has collected, and their roots are embedded in that debris, which consists primarily of shed bits of bark mixed with decomposing leaves. The epiphytic orchids, OTOH, seem to grow more on the surface of the bark, with their roots exposed to the air. The little pockets of decomposing vegetation would be more on the order of very coarse compost, I think, so a regular potting mix with materials like orchid bark or coir ... or even, as I've been using, commercial cactus mix ... added to improve drainage ought
to be a close match to what the plants prefer in their native habitat.
The next time I repot my large holiday cacti, they'll be going into 12" containers, so I think I'll get some orchid bark and mix that it. It would definitely make a big improvement in the drainage when using a large container. Good idea, AS! Thanks for the hint!