Switching seedlings from sphagnum to s/h

[ECC_lectic]

I am trying a new, ambitious and I hope successful experiment. I am setting up a modified "living wall" for about 30 cattleya and epidendrum seedlings (all miniatures, 1-2 years away from flowering).

I've made the main structure - it is a large, flat "pipe" with a long, narrow x-section. One surface will be against the wall, there is a 4" (10 cm) gap between the front and back surfaces, and the front surface has 30 holes that 3" net pots fit into at a slight downward angle from horizontal. So the seedlings will be growing almost vertically. The sides are solid, measuring 5" (13 cm) on the outside. The material is cement based, fibre reinforced composite, with 12-15 mm thick walls. The cementitious material has a fairly low pH, around 9, and I plan to seal it anyway.

The front and back surfaces measure 30" wide by 48" high (76 * 120 cm). Inside the 4" gap, I will install 3 misting nozzles, and the pump will reside in a trough at the bottom of the "pipe". This trough will serve as the reservoir and catch basin for drips. Except for the trough and the narrow ledges it rests on, the bottom and top are open. There is also a full perimeter drip edge just above the trough. Sorry, no pictures until after the holidays.

The seedlings came from a very reputable local greenhouse, but like every other commercially grown orchid, they're growing in sphagnum, in 2" plastic pots. I need to transfer them into 3" net pots and into an inorganic semi hydro medium. I plan on using a perlite and charcoal mix, but I'm very open to advice on why I should or shouldn't use something else.

I don't know how successfully I will be able to remove all the sphagnum. I want to keep root damage to a minimum, so my first question is, is there any harm in leaving some sphagnum in this environment? Am I condemning the sphagnum covered roots to rot anyway? If there is harm, what is the best (least root-damaging, but not necessarily fastest) method for removing it?

My second question: how often should I change the water in the reservoir? I use Dyna-Grow liquid fertilizer (7-9-8), with filtered water. I will also have a debris filter for the pump. Is there a systemic, reasonably non-harmful fungicide I can add to the fertilized water to increase its useful life? Sulphur or copper powder maybe? Or colloidal silver?

Third question: how often, if at all, should I run plain water through the pump?

Fourth question: what pitfalls have I not considered?

Thanks in advance.

[ECC_lectic]

A couple of corrections - I guess if I'm using charcoal in the medium, I can't call it inorganic. But I do want one that will not be bio-degradable.

I also have one photo, of the structure still in the form. Only the front surface is visible, although it's obvious that the entire piece is 5" thick. The front surface is about 5/8" (15 mm) thick, then buried inside are two sheets of 2" styrofoam, and the back surface is at the very bottom, about 1/2" thick. The pink circles are the blockouts for the holes for the net pots. I originally made mostly 2" circles, but I've since had to enlarge them to 3" after I saw how tiny the 2" net pots really were.

The tree branch is there for decoration only, I'm not planning to mount any of the orchids. The dumbbell is pressing down on an unruly twig to embed it in the surface.

[raybark]

You would probably be better, long-term, using LECA instead of a perlite/charcoal blend. In addition to being friable and apt to crumble under root-growth action, the perlite carries a lot of potassium with it, which can lead to fungal resistance issues in the future, and while the charcoal absorbs really well, it doesn't release solutions well, leading to more-rapid buildup of minerals, and the need to replace it.

You really should get almost all of the sphagnum off of the roots; it will decompose eventually, and is a risk for maintaining a pathogen-rich environment. I would not suggest using a preventive fungicide treatment, as evaporation of the water will concentrate it, potentially to dangerous levels. Same is true of fertilizers.

I recirculate from a sump, and replace all of the solution weekly. If you can rig up a standpipe and a timer to periodically overflow it to the drain, it'll reduce the labor significantly.

[ECC_lectic]

Thanks Ray. Overflow and drain are not an option, as this setup will be in my living room. I will have to pull out the trough and replace the solution. How often should I flush the system with pure water?

Also, I forgot to mention - all the seedlings have fresh moss growing on the surface, often completely covering the rhizome. Should I remove it too?

[raybark]

I think the live moss will be of no consequence, and it's above the medium anyway. It's dead moss trapped in the medium that's an issue.

I cannot say how often-, or even if it is necessary to flush with plant water. Mineral buildup only occurs if there is significant evaporation from the substrate. If the RH in the chamber is high enough, then everything stays moist and there will be little-to-no buildup. In that situation, doing a periodic dump-and-replacement of the very dilute nutrient solution will maintain a very low level of minerals in the overall system, which is of no consequence.

[nlnelson]

The live moss has never hurt any of my mini-catts. And if your seedlings came from the nursery that is outside of St. Catharines, then I'm betting most of your minis will bloom this year, if not this spring (they always overestimate time until blooming). It sounds like you'll have quite a show on your hands when they all get established - good luck!

[ECC_lectic]

Thanks Nicole, you are correct. Some are very overgrown. I just hope that they like their new home.

After the holidays, I will be installing the living wall and the plants, so I will have some photos to post. All the components are in except for the light fixture. I was going to use a 2 foot long high output T5 fluorescent fixture. As much as I would like to get away with only 2 tubes, I think I will have to use 4. I plan to mount the light on a computer monitor arm so that I can position and aim it better. The wall I'm putting the living wall onto is about 12 feet (3.6 m) away from my south facing living room window, directly opposite.

[ECC_lectic]

Well, the easy part is done. The empty structure is cleaned of all styrofoam (took over a gallon of acetone and more than a few choice words), sealed and fastened to the wall.



For some reason, the photos show up rotated 90 degrees. They're oriented correctly on the computer. Sorry, I don't know how to fix this.

There are 26 holes for 3" net pots and 3 holes for 2" net pots. Now comes the hard part. First, I need to set the lithium silicate sealer with vinegar, inside and out. The vinegar crystallizes the silicate and creates a microscopic glass layer on the surface. It also drops the surface pH to pretty much neutral level. This chemical reaction is why you cannot mix a potassium silicate plant strengthening solution with an acidic fertilizer, or you will get useless sludge.

I also need to attach a drip edge to the inside back wall. The other three drip edges molded perfectly, but the back wall had gravity working against it, so I'll glue in a stainless steel strip. The trough is ready, but I haven't been able to pick it up from the steel fabricator.

Then I need to set up misting nozzles inside the wall space, and adjust their position to provide the best coverage. I'll probably attach some kitchen cabinet door handles on the inside back surface to fasten the nozzles.

I've ordered some LED bulbs, so when they arrive, I will need to set them up on the outside for maximum coverage. I will probably end up making my own fixtures, I haven't seen anything in stores that would be suitable for this setup.

And then the really fun part - repotting the seedlings and setting them in. Can't wait.

Here are a couple more photos - a straight-on view and inside, looking up.

[Polarizeme]

This is very cool. How goes the planting and other particulars? I am curious to see the finished wall!