# Rockwool Cubes + LECA



## Ernesto (Sep 27, 2020)

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!


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## Ray (Sep 27, 2020)

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.


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## Geek_it (Nov 8, 2020)

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?


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## Ray (Nov 9, 2020)

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.


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## terryros (Nov 9, 2020)

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.


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## Geek_it (Nov 9, 2020)

Ray said:


> 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!!!


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## Ray (Nov 10, 2020)

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.


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## ScientistKen (Nov 23, 2020)

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.


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## terryros (Nov 24, 2020)

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?


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## Ray (Nov 24, 2020)

terryros said:


> 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.


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## BrucherT (Nov 24, 2020)

Ray said:


> 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!


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## terryros (Nov 24, 2020)

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.


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## southernbelle (Nov 24, 2020)

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.


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## Ray (Nov 25, 2020)

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


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## terryros (Nov 25, 2020)

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).


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## Ray (Nov 26, 2020)

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.


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## terryros (Nov 26, 2020)

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.


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## Ray (Nov 26, 2020)

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.


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## ScientistKen (Jan 12, 2021)

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


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## Ray (Jan 13, 2021)

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:

100% LECA in semi-hydroponic culture.
50% Rock wool cubes/50% LECA in semi-hydroponic culture.
50% Rock wool cubes/50% LECA in traditional culture.
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.


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## Geek_it (Jan 13, 2021)

Ray said:


> 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:
> 
> ...



Hey rey, with the 50/50 mix, how long before it fries out and needs to top up with watering


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## littlefrog (Jan 13, 2021)

Are they actually that yellow or is it an artifact of lighting?



ScientistKen said:


> Here are a few dalessandroi plants I've been growing in a mix of rockwool cubes and hydroton. They seem to like the combo.
> 
> View attachment 24639


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## Ray (Jan 13, 2021)

Geek_it said:


> Hey rey, with the 50/50 mix, how long before it fries out and needs to top up with watering


I never "top up" anything. All waterings are floods, so that the medium is flushed and saturated with fresh material. Indoors, in my conditions, I water once every week to ten days - trying to keep it to a max of a week, but you know...


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## terryros (Jan 13, 2021)

Ray, what are you arriving at for fertigation concentration and frequency with the two 50:50 situations?


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## ScientistKen (Jan 13, 2021)

Thanks for update. 
I get confused about terms. Is LECA the same as Hydroton or are they different brands? 

I have tried 100% and it works, like you say it can be wobbly at first especially on small plants. Also wobbly when you initially plant if you plant with dry cubes before watering. I've done it both ways and there are pros and cons both ways. I like that the cubes provide some geometry and precision. It kind of makes up for the wobbly start because you can make adjustments. 

I agree with your conclusion. I think I like the 50/50 better. It provides more air to the roots and helps reduce wobbliness. I have had best luck with besseae and kovachii hybrids. Lindleyanum have not had good color. There may be something else going on or it could be excess moisture or nutrient deficiency. This inert medium approach may be more fussy with nutrient deficiencies and pH. I plan to get some Kelp Max from Ray.


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## ScientistKen (Jan 13, 2021)

One more thing. For moss lovers, moss is almost automatic. The example I posted does not have much moss out of the ones I have growing this way. It's common to be solid moss at the top.


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## Ray (Jan 14, 2021)

terryros said:


> Ray, what are you arriving at for fertigation concentration and frequency with the two 50:50 situations?


Terry,

I made the switch in some (most) of those just before coming indoors for the winter, so most of my experience is in a somewhat cooler, drier environment. I always water with K-Lite, and try to keep up with once a week @ 100 ppm N, but that has occasionally slipped a few days. Once a month I add KelpMax and Quantum. In the summer, when the plants are out on the deck, where it is much warmer, far for humid, and with brighter light (still indirect, as they’re along the north side of the house, just outside the Low-E windows they’re in front of now), I feed at 50 ppm N about twice a week.


ScientistKen said:


> Thanks for update.
> I get confused about terms. Is LECA the same as Hydroton or are they different brands?
> 
> I have tried 100% and it works, like you say it can be wobbly at first especially on small plants. Also wobbly when you initially plant if you plant with dry cubes before watering. I've done it both ways and there are pros and cons both ways. I like that the cubes provide some geometry and precision. It kind of makes up for the wobbly start because you can make adjustments.
> ...


LECA is an acronym for Lightweight Expanded Clay Aggregate, of which Hydroton is but one brand name.

I don’t consider inert media to be “fussy” about nutrition. If anything, I think it gives the grower more control, but then again, I’ve been growing in S/H culture for 30 years, so I’m kind of used to it at this point.


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## NYEric (Jan 14, 2021)

A nice science experiment. keep us posted.


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## NYEric (Jan 14, 2021)

ScientistKen said:


> Here are a few dalessandroi plants I've been growing in a mix of rockwool cubes and hydroton. They seem to like the combo.
> 
> View attachment 24639


Scary light levels!


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## Sky7Bear (Jan 14, 2021)

I am also working with inorganic media, mostly semi-hydroponic, though I have a few in a 50/50 mix in traditional culture. I find that the top layer dries out to fast if I don't put some sort of "lid" on it--at the moment, small aquarium gravel. The beauty of growing this way is no more throwing away rotten bark (Terry Root used to repot 2 x a year at the Orchid Zone). What a waste of time and resources. Many of the Paphs and Phrags in nature are already growing at least partially lithophytically. Air to the roots is, I believe, an essential ingredient in any orchid culture, and probably the ratio varies by genus and perhaps in some cases even species. Thanks, Ray, for taking the lead on this and for doing your work scientifically and reporting it.


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## ScientistKen (Jan 15, 2021)

NYEric said:


> Scary light levels!


I kind of wonder about that. They are growing well, though. Came out of flask in September 2019, so 16 months. The biggest one has over 6" leafspan. I have another compot with mostly medium sized between the largest and smallest in this compot.


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## terryros (Jan 16, 2021)

I agree that oxygen is under appreciated and essential for roots. It is not transported down from the leaves. Large particle media like LECS, lava rock, river rock, etc give great air space for the roots, but require frequent fertigation. Each of us has to figure out the balance of watering frequency we can provide and maintenance of air space for the types of orchids we grow. Ray has shown us good data and a method for a roughly once a week fertigation by providing a water buffer with rock wool. If you can fertigate frequently, you could be moving toward all rocks.


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## ScientistKen (Jan 16, 2021)

terryros said:


> I agree that oxygen is under appreciated and essential for roots. It is not transported down from the leaves. Large particle media like LECS, lava rock, river rock, etc give great air space for the roots, but require frequent fertigation. Each of us has to figure out the balance of watering frequency we can provide and maintenance of air space for the types of orchids we grow. Ray has shown us good data and a method for a roughly once a week fertigation by providing a water buffer with rock wool. If you can fertigate frequently, you could be moving toward all rocks.


I use river rock quite a bit. I like lava rock, but it often tears up roots at repotting. But from an oxygen standpoint, I think that has to be one of the best.


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## Ray (Jan 17, 2021)

If you do the math, 100% perfect spheres of the identical diameter offers the most free space. Anything that is irregular in shape or non-uniform in size has the opportunity to intrude into the spaces created by its neighboring particles, reducing that open volume. That is a good reason to avoid mixing coarse bark with smaller pieces of charcoal and perlite, for example.

That said, stuff like lava rock, being as jagged as it is, tends to get “hung up” before having an opportunity to settle, so I’m sure that keeps it more open than it could be.


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