You know how there are some people who say, “_______ is the best way to grow orchids”, when referring to bark or sphagnum or semi hydro? And then a bunch of other people will say, “everything works differently in your individual climate”?
That’s obviously true…but maybe there’s a nugget of science that can help us all understand why one method or potting media works for a person (while that same method could be catastrophically bad for another person’s orchid collection)…
I did a pretty simple experiment to test the water-holding capacity of different orchid media and the subsequent dry-out rate (in my climate). The results were pretty interesting.
The question: Which orchid media holds the least/most water and what effect does that have on the dry-out rate?
In other words: which potting media will dry faster or slower (or too fast in a dry climate vs. too slow in a humid climate)?
How Much Water is Held by Each Media Type (When Saturated)
* Roughly 1/2 cup of Media by volume was used and soaked for 30 mins
- LECA: 27.4g of water
- Pine Bark: 37.02g of water
- Blended (Fir bark, pumice, sphag): 50.77g of water
- Sphagnum: 102.4g of water
These results show that LECA holds the least amount of water and sphagnum holds the most—nearly 4 times as much water when compared to LECA. Bark and a blended mix fall somewhere in between. If we extrapolate this a bit, it might be clear why some people love sphagnum, while others love LECA.
For some people, in their climate with their watering routine and the type of orchid they’re growing their media might “just works.” If your climate has a low humidity (under 40%), then LECA could go bone dry within in a day or two (or at least the top-layer could if you’re using semi-hydro). Conversely, if your humidity is high, then saturated or old / compacted sphagnum moss might still be wet after a full week—which is bad because those conditions are favorable for some fungal pathogens like fusarium.
This is why I use a blended mix – I can customize the dry-out rate based on the needs of the orchid AND MY CLIMATE. If I want it very moist, I use pure sphagnum (or a lot of sphagnum); if i want it moist but airy, I’ll use a bit of sphagnum but also add bark and perlite; if I want it to dry quickly, I wont use any sphagnum and I’ll use large chunk bark so that air can flow freely though the media (increasing the evaporation rate). You can check out all of the potting mix “recipes” I use for my orchids here.
This type of simple experiment is probably a bit of a no-brainer. It does help illustrate the value of testing and analyzing things so that we can become better growers and I hope this helps give others (new growers especially) some perspective on different orchid medias and their relationship to a person’s climate. It’s also illuminates why some things work for one grower, while they might not work for you…maybe it all just comes down to water retention, evaporation, and humidity?
If you want to see the rest of the results, check out this google sheet. I’ve tabled the timed readings and included some graphs that illustrate the dry out period over time.
Anyways, remember to always test your theories, don’t accept what other growers say as fact and enjoy the process of learning about plants. It’s how you become a better grower 🙂