Rockwool Cubes + LECA

[Ernesto]

I started collecting paphs back in February, and since then I’ve really hit my stride with finding how they best grow in my space. Given my average temps and humidity (70-79 F and 65-85% in the summer, 68-73 F and 45-65% in the winter) I’ve found they do really well in a mix that is about 3:1:1 Orchiata, charcoal, and perlite, topped with a small amount of oyster shell and sphagnum moss. For me the biggest game changer has been the addition of sphagnum as a top dressing, together with KelpMax and Quantum Total probiotics— huge burst in root growth following this combo of extra moisture and additives.

There are drawbacks here, though. I’m currently watering (~30 ppm N, K Lite) every four days. When the pandemic is over I don’t see myself having nearly as much time on my hands to baby my plants. Also looking to the future, buying bulk bags of Orchiata annually hurts my wallet. This leads me to wanting to seek out a solution that requires less frequent watering and one that utilizes inert media I won’t have to replace every year or two, while still being water retentive and airy like my current mix.

Currently I’m thinking of going semi-hydro, with a top dressing of rockwool. Would this combat precipitation of salts at the dry line? While also being gentle on new emerging roots, much like I’ve seen with sphagnum moss top dressing?

My tap water, after gassing off for a couple days, sits at about 7.0-7.3 pH and 70-85 TDS (depending on time of year). About how often will I need to flush to prevent the buildup of salts present in my tap water + fertilizer?

And lastly, will the time saved be worth it? Will I be able to comfortably move from watering every 4-5 days to weekly waterings?

Thanks for reading!

 

[Ray]

In my limited amount of experimentation so far, I find that a mix of Grodan mini-cubes and LECA precludes the need for any top dressing. It's as if the cubes, holding as much water as they do, act as little reservoirs throughout the mix, supplementing the one at the bottom.

I have a pescatoria in a 50/50 mix in an air-cone pot with no reservoir and lots of air from the bottom slots and cone, and it's been 10 days since I last watered it, and it's still moist.

 

[Geek_it]

Hi ray.... would maudiae type/hybrid grow ok in small lava rock + pumice in self watering pot?

What are the signs if its in trouble in this set-up?

 

[Ray]

G_I - it ought to be fine, although I don’t have a feel for that particular medium.

When I was developing the semi-hydroponic technique for orchids, paphs were my first “guinea pigs”, and they did so well (they took to it with no issues at all) that I was encouraged to try other stuff.

 

[terryros]

Ray, several things I remember from you were triggered by the Rockwool chains. The first would be paraphrased, “You could grow orchids in marbles, if you fertigated with low concentration nutrients frequently”. I then remembered your noting that some of your best results with LECA/SH were with daily watering from the top with dilute nutrients. This washed away wastes and provided constant nutrition like happens in the natural environment. The LECA/SH also provides constant oxygen, which is critical for the roots.

That led me to believe in using some form of inorganic media (OK, rocks of some sort) with frequent low concentration of nutrients, which is what I have been using for everything for about 2 years.

I had several Phrags in rock wool and the medium really stayed “wet” for many days. Accepting that there is air inside the rock wool somewhere, I worry how the oxygen gets ”renewed” in the Rockwool if watering is infrequent. Does it just diffuse in? Infrequent watering also decreases waste removal and means you will use higher concentration of nutrients less often?

Since I am able to fertigate my plants fairly frequently, I didn’t see an advantage of using Rockwool with less frequent, higher-concentration fertigation? However, maybe you can still fertigate Rockwool every 3-4 days with lower concentration solution even though the Rockwool is still very wet? I didn’t want to try that.

Finally, as your old comment about the marbles suggested, many orchids are very adaptable and can adjust to all sorts of media and fertigation systems. Rockwool might be great for someone who wanted to fertigate less frequently.

 

[Geek_it]

G_I - it ought to be fine, although I don’t have a feel for that particular medium.

When I was developing the semi-hydroponic technique for orchids, paphs were my first “guinea pigs”, and they did so well (they took to it with no issues at all) that I was encouraged to try other stuff.

Thanks Ray!!!

 

[Ray]

Terry,

That’s a good observation!

As I no longer have a greenhouse with automated irrigation I can adjust at will, I have moved to the “less frequent” category again. I don’t think there is much air within the individual rock wool cubes, but the void space in the pot stays about 40%-45%, so I am less concerned about that.

I don't recall if I posted this here, but it won’t hurt to duplicate. I filled three 3.5” square pots (Chula Orchids clear version of a McConkey pot) with Mini-cubes, a 50/50 mix with LECA, and LECA. The pots have holes in the bottom only. After weighing dry, I watered them using an overhead “rain” head on a watering wand, as I would treat my plants. 15 minutes later, I repeated that to saturate them pretty thoroughly.

They were kept in my “First Rays room”, a very small room in the back of my garage where I keep inventory and do my packing. During the test, the conditions were fairly stable at 75-81F & 60-67%RH.

The more observation I do, the more I am leaning to the blend, if for no reason other than it’s heavier weight provides better mechanical stability. For mass of water held, the “100%” level was 900% the weight of the cubes, about 100% for the blend and roughly 25% for the straight LECA.

 

[ScientistKen]

Love your chart, Ray! I have used 100% cubes, 50/50 w/ LECA and also a few other combos with perlite charcoal and even bark. Your graph is similar to what I think is going on in my pots in my basement. But outdoors the pots seem to dry out faster even when humidity is 80%. I like the LECA in there for similar reason: mechanical stability (in addition to helping some drying take place). The LECA helps me get the plant situated until the roots take shape in the new pot.

 

[terryros]

Ray, let me corner you this way. IF you had complete control of all growing conditions, had help (automated or manual) to water/feed optimally, but were still going to use pots, what potting media would you use and how would you fertigate?

 

[Ray]

Ray, let me corner you this way. IF you had complete control of all growing conditions, had help (automated or manual) to water/feed optimally, but were still going to use pots, what potting media would you use and how would you fertigate?

With that “use pots” constraint, as odd as it may seem - definitely glass marbles. They are 1) perfect, uniform spheres, so the open volume is the highest possible, 2) weighty, so provides stability in the pot, and 3) non-porous, so will not accumulate residues and will flush clean at each watering.

Fertigation would be with a low-concentration fertilizer in pure water, likely via an overhead deluge (“rain”) system, but I suppose a drip tube irrigation system would also work, if for no other reason than to keep the foliage dry.

 

[BrucherT]

With that “use pots” constraint, as odd as it may seem - definitely glass marbles. They are 1) perfect, uniform spheres, so the open volume is the highest possible, 2) weighty, so provides stability in the pot, and 3) non-porous, so will not accumulate residues and will flush clean at each watering.

Fertigation would be with a low-concentration fertilizer in pure water, likely via an overhead deluge (“rain”) system, but I suppose a drip tube irrigation system would also work, if for no other reason than to keep the foliage dry.

Now I want to try glass marbles!

 

[terryros]

That is what I had been thinking. I have quickly looked at marble sources. I think I would use clear and need to find where to get a decent volume of them at reasonable price.

 

[southernbelle]

Very interesting dialogue!! I think I remember reading in the Grodan (Rockwool) literature somewhere that the current mini cubes are both hydrophobic and hydrophilic at 50/50. I am only using them for besseae hybrids with about 60/20/20 mix with perlite and charcoal with about a teaspoon of oyster shell on top that filters down into the mix with watering. I let them dry a bit on top, between watering, but 3” pots water at 3-4 days and 6” pots at 6-7 days. These are growing in a large east window at current day temp of 77, night 68 with humidity ranging 50-60%. I have a small oscillating fan on low, running on them all the time. They have all recovered from the temps being too high (84 summer) in my grow room and are now doing well. But, I have to say I also have an 8” pot of Eumelia Arias in Power + Orchiata mix (4 days), and a 4” pot of Nicholle Tower in Power Orchiata mix (2 days) growing along with them that are extremely happy. I’ve been told by expert Phrag growers that the Power and Power + are way too large a mix for phrags, but these particular plants (non-besseae) seem to love it, so I’ve left well-enough alone. Didn’t mean to hijack the thread, but wanted to share a different experience.

 

[Ray]

@terryros @BrucherT moonmarble.com says they sell in bulk. I’d probably go with the 5/8” ones.

 

[terryros]

Thanks. I have to do a marble experiment or I will always wonder. A Phrag and a Catt that need dividing, one in marbles and one in what they have been in (I am not saying right now).

 

[Ray]

When I was a new grower, I grew a phal in marbles. It had to be watered at least once a day in a windowsill environment. Nope. Too much work.

 

[terryros]

Yep, practicalities always get in the way. Watering every 3 days is doable for my collection, so something in between marbles on one end and moss on the other. I think rock wool is a little too much toward the moss end for me. Some kind of rock seems to work best for me.

 

[Ray]

You might give the rock wool-LECA mix a try. Sort of a “best of both worlds” scenario.

I’ve been quite impressed with how well my plants have responded to it.

 

[ScientistKen]

Here are a few dalessandroi plants I've been growing in a mix of rockwool cubes and hydroton. They seem to like the combo.

 

[Ray]

Since Ken posted, I'll offer a little update on my experimenting.

As of maybe 6-8 weeks ago, 100% of my plants are in inorganic media; some in each of:

1. 100% LECA in semi-hydroponic culture.
2. 50% Rock wool cubes/50% LECA in semi-hydroponic culture.
3. 50% Rock wool cubes/50% LECA in traditional culture.
4. 100% Rock wool cubes in traditional culture.

Everybody seems happy - those in 100% cubes are a bit wobbly until the roots have really grown - and I am leaning toward the two 50/50 options as I move forward.