2 unrelated questions: rock wool and plant walls

[camille1585]

I'm seeing these two things over and over again on the french orchid forum, and I don't know what to think of them.
First, a lot of people swear by rock wool as a medium for their orchids. Is this a good idea? From what I know, if it dries out it acts like a sponge and pumps water out of the orchid roots, and I think salt buildup might be a problem. pH and conductivity have to be constantly monitored from what I read.

The second thing is a plant wall. Orchids are mounted on a felt-like fabric and water drips from the top every 5 minutes to water them. The unused water drips into a tank, and then is recirculated with a pump. The final thing looks so cool and saves a lot of space, but I would be really worried about spreading diseases! Any one have experience with this?

[cowboy51278]

one of my trusty books says that there are two types of rock wool. One that absorbs water and another that repels water. By combining them you can acheive different water holding capacities. Its totally decay resistant and pH neutral. The book says it requires some practice to use effectively and fertilizing can be tricky. Its also UGLY as all get out. It also says that you need to pack it in "dangerously" tight to stabalize the plant.

do they have any pics of the plant wall? that sounds kind of interesting.

[Magnus A]

Hi Camille

I grow some Phragmipedium in Greenmix (rockwool mixed with perlit). They grow in semi-hydro with the pots standing in about 2 cm water. The "pumps water out of the orchid roots" is most often told but I do not think this is a problem. The problem, in my oppinion, is that roots adjusted to be constant wet is more sensitive to dry conditions.
One drawback is that the material is VERY dusty when it dries and hard to handle without proper protection.

/Magnus

[camille1585]

Paul, here's a link with some pictures of plant walls. Scroll down the page, as there are several different ones. There's a really nice one near the bottom. (sorry the website is in french!)
Forums Orchidées- Plant walls

I really want something like this!!

[Ross]

Rockwool is spun fiberglas. This has no way to hold water except through capillary action - kinda like using marbles as potting medium, only smaller. There are many different fiberglas products, some rigid, some fiberous and soft. All have same properties (more or less).

The plant walls sound like a valid way to care for certain orchids that do not need a drying of the roots.

[cowboy51278]

Originally Posted by camille1585

Paul, here's a link with some pictures of plant walls. Scroll down the page, as there are several different ones. There's a really nice one near the bottom. (sorry the website is in french!)
Forums Orchidées- Plant walls

I really want something like this!!

Lucky for me I took 5 years of french

They are really amazing. I only saw a few orchids on the last wall. The rest seemed to be mostly ferns. Maybe thats why they're getting away with recycling the water? I don't think ferns care much about that, and if you only have a couple orchids on the wall what are the chances that they're be at risk? But a great idea. I want one.....in my livingroom (sooo not gonna happen )

[Ocelaris]

Fiberglass is a tad different from rockwool. The difference being that one (fiberglass) is silicate, or quartz based, and has no pH effect, and is typically not used in gardening; where as rock wool is a spun granite or carbonate based which has some pH buffering ability. Historically, USA used mainly fiberglass products for insulation where as Europe used rockwool.

Ross is right, they can be made into all sorts of varieties, hard, soft, stiff, dense, loose... and they only work by capillary action

The two "types" of rock wool are in fact actually the same thing but one has been acid washed so that it is hydroscopic not hydrophobic like the process of spinning the granite makes it by default. The pH will rise over time, so you do need to keep an eye on it or you will get nutrient lockout as pH rises.

I would say that rockwool typically has too much water holding capability, such that you will suffocate most orchid root systems. Only as an addition with maybe a highly draining material like charcoal or coconut husks which have no water holding capacity.

[Ray]

I hate to do this Ocelaris, but my ceramic engineering background won't let me stop.

Both rockwool and fiberglass are silica-based glass fiber materials, but the formulas of the raw materials used in the glass melting process are entirely different. I suspect that in both cases, the idea is to use the cheapest available raw materials that give the fiber properties sought.

Rockwool products tend to have relatively short fibers, while insulating fiberglass strands tend to be longer.


All such glasses are based upon a silica "backbone" to which various alkaline earth modifiers are added to lower the melting temperature and viscosity. Pure SiO2 will melt at about 2000°C, but at that temperature, the viscosity is so high, you cannot work with it. By adding modifiers, you break the Si-O-Si bonds to improve the workability, but it degrades the durability of the glass.

The acid treatment of the fibers extracts the "dangling" alkaline species to adjust the surface pH downward, but it really has a relatively little effect on the hydrophobicity. That is usually controlled via coatings, and their adhesion to the glass can be affected by the surface chemistry.

[Des]

Been there done that ,wont be doing it again ever again. !! i found rock wool or culti wool as it is sometimes called here a complete disaster. Dont get me wrong Orchids grow very well in the stuff ,but so do weeds ferns and just about everything that can will germinate in your pots so that you spend a lot of time just weeding your pots Maidens hair ferns love it and if left for too long they are just about impossible to remove without breaking up the orchids root system . My advice is dont go there !!

[dave b]

Ive started using rockwool for a few of my phrags, and so far they like it. Only been a couple months though. I have several house plants growing in it, and they love it.

Several of our society members use it, primarily for phrags, or blended with hydroton for paphs. They have great success with it. One of them traveled overseas last year and visited the Eric Young Foundation. While there, he found its their main medium for phrags. He has since started converting many of his water loving types over to it.

It does 'hold' a lot of water, but also allows for good air. I do not pack it in real tight. You are not to let it dry completely, as it does hold salts, and can burn the roots if dry.

I think its great for water loving types like phrags, but would be leery of using it with most other types.