Can tree fern fiber be harmful to orchids?

[OrchidThief79]

I read in a book that tree fern fiber used as a medium can eventually become "toxic" to orchids. It was a reputable book written by an orchid expert, yet I haven't seen any other mention of this anywhere. Does anyone know if this is true? If so, does anyone know why? Thanks.

[King_of_orchid_growing:)]

Do you have the exact quote from the book?

I personally don't think that tree fern fiber is toxic to orchids. However, I do know that they can decompose rather quickly and happen to retain moisture for quite a while, especially when it's used in conjunction with Sphagnum moss.

Some orchids don't appreciate being kept this wet. The prolonged exposure to moisture will eventually cause root rot, even amongst moisture loving plants such as Masdevallias.

[susiep]

I use tree fern a lot and have never experienced this breaking down problem. However, the author may be talking about using the tree fern crushed into small pieces and used in a potting mixture. I have seen it used in large pieces (chunks) in a wood basket and it definitely does not hold moisture very long. I mainly use it as slabs for mounting or the tree fern pots. They are especially good for phals that like lots of air to the roots. I am growing a neo falcata in a tree fern pot, too. The tree fern does tend to crumble as it gets older, but to me that is good. Easy to just break it away from the roots and repot or remount the plant.

[King_of_orchid_growing:)]

Edit: I personally don't think that tree fern fiber is toxic to orchids. However, I do know that they can decompose rather quickly and happen to retain moisture for quite a while, when it's used in conjunction with Sphagnum moss in a potting mix.


Tree fern mounts retain most of the moisture closer to the core of the mounts. While tree fern mounts are slower to break down, it crumbles very easily.

[Royal]

I've always understood that tree fern fiber lasts a very long time. The few plaques and pots I have picked up over the years are still in good shape.

My guess is that the author may have been referring to an accumulation of salts over time. It may become "toxic" due to salt buildup but still appear as if it's in good shape since it lasts so long. Most other media will break down and look old by the time salts build up to toxic levels.

[tucker85]

Old time growers in South Florida have told me that years ago tree fern fiber was the "go to" potting medium for Cattleyas and other orchids that like to dry quickly. They changed when tree ferns became scarce and the fiber became expensive. Tree fern fiber has a reputation for not breaking down very quickly. That's one reason that it's used for mounts. I would guess that Royal was correct in thinking that the author was probably talking about accumulated salts which can make almost any medium toxic over time.

[Andrew]

I don't have experience with using treefern as a potting medium but treefern mounts can become acidic over time. I presume the same would happen if it's used in a pot. Some orchids are tolerant of the increasing acidity, while others are not. In Australia, the more commonly available Dicksonia mounts are prone to becoming too acidic while Cyathea mounts usually don't seem to cause problems so I don't know whether you're likely to have issues with the treefern species you have available in the US. If there are problems, adding lime to the treefern every so often will buffer the falling pH.

[susiep]

Andrew, that is very interesting! How would I go about adding lime to the pots and mounts without hurting the plants? As a dilute dunk/soak, perhaps? What product should I use? Thanks!