# Rockwool chunks



## eds (Dec 27, 2021)

Rather than take the grow cubes and LECA thread off topic I've started a new thread.



eds said:


> Ray,
> Have you tried any of the grodan chunks, the larger pieces? (I have bought a bag of both sizes to experiment with.)
> 
> I grow most of my Phalaenopsis hybrids in glass cubes. Currently I use large orchiata but was thinking I could switch to these large cubes for them and keep a more even hydration through the cube than happens with the bark. My train of thought was that the larger voids would allow more air spaces for the roots - what do you think?





Ray said:


> I have not, but as long as you can avoid having the cubes stack face-to-face, you might be alright.
> 
> I planted a couple of very similar divisions of a mottled-leaved Paph in a ~67/33 mix of the mini Grodan cubes and LECA, but one is blended, while the other is in layers. It’ll be interesting to see if they differ in root growth.View attachment 31285



Today I have potted up two of my hybrid Phalaenopsis in the larger grow chunks. One of these is a white NOID hybrid in a 10cm x 8cm x 14cm t(4"x3"x5.5") all-glass cuboid vase. The other is a Shih Hua Gold in a 15cm acrylic cube.

I am hoping these chunks may allow greater air spaces than the smaller cubes for the Phal roots to navigate while giving me a much more even gradient of moisture in these vases.
This is a picture of the Shih Hua Gold before repotting to show the issue,


This was soaked a couple of weeks ago and then has been watered from the top with a sprayer, the last time about four days ago. The bottom is still moist while the top half is dry. On repotting it was a similar story all the way through due to the coarseness of the orchiata bark.

This is the same plant not repotted in rockwool chunks.


Interestingly the water you can see in the bottom has drained out of the chunks since I drained off all the water. The top chunks are already slighter lighter (and I assume drier) than the lower ones but certainly much more even than the bark used to be.

The NOID needed some root pruning to to get it back into the smaller vase but I didn't want to pot it on as it never makes a huge plant. The grow chunks had to be manipulated into place much more with this plant.



Will post back here once I see some action, hopefully positive!

If anyone else is using them and wants to post some pictures / experiences then please do.


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## NYEric (Dec 27, 2021)

No drainage hole? Good luck.


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## eds (Dec 27, 2021)

NYEric said:


> No drainage hole? Good luck.



Haven't used drainage holes with my Phalaenopsis for nearly 20 years. In my home it allows me to have them on the windowsill without faffing with trays or outer pots. The enclosed container seems to help keep the roots moist in the dry home environment and means I have very few aerial roots. I water them by filling the entire vase, setting a timer for an hour and then tipping the water out.

I'm hoping the rockwool will take longer to dry out than the orchiata does currently and stay more evenly moist. If I don't need to repot as regularly that will be great too!


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## NYEric (Dec 27, 2021)

That's an old Vanda watering technique! Good luck.


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## eds (Jan 20, 2022)

Early days for this trial but first impressions are looking good. It seems to be doing exactly what I hoped - the moisture seems much more even over time. I have watered twice since repotting (with TNC mycorrhydro and Maxicrop as I have treated all my orchids with that). Apart from that, they have only had one small spray when the surface blocks looked really dry. (Compared to my bark grown phals which get at least one spray a week usually.)

No sign of any new roots yet but the existing ones seem happy so far.


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## BrucherT (Jan 20, 2022)

I’m curious why not just straight water culture?


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## Tony (Jan 20, 2022)

I switched to rockwool/perlite three years ago and I love it, I don't see any reason to go back to organics. I do grow in pots and baskets though, not any kind of semihydro or undrained setup. I can water every day during our hot summers without having to worry about root rot or media breakdown.


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## eds (Jan 20, 2022)

BrucherT said:


> I’m curious why not just straight water culture?



Honestly, because I didn't know it was a thing outside empty jars with Vandas in! Plus the bark in cases has worked pretty well for me in my home and I hope this will be an improvement.

Thanks Tony as well. I'm certainly liking it so far.


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## Ray (Jan 21, 2022)

FWIW, in my experience, straight rock wool cubes ended up being insufficiently airy for my preferences, because the flat surfaces “stacked” too easily, as can be seen in places in the original photos. I think it really pays to add “something else”, even in a small amount, to help break that up.


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## spes1959 (Jan 21, 2022)

Ray said:


> FWIW, in my experience, straight rock wool cubes ended up being insufficiently airy for my preferences, because the flat surfaces “stacked” too easily, as can be seen in places in the original photos. I think it really pays to add “something else”, even in a small amount, to help break that up.



Hi Ray if I'm not mistaken you suggest using a third of rock wool and two thirds of LECA. I ask you if this proportion can also be good for Cattleya


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## Ray (Jan 21, 2022)

spes1959 said:


> Hi Ray if I'm not mistaken you suggest using a third of rock wool and two thirds of LECA. I ask you if this proportion can also be good for Cattleya


There's no "one size fits all" answer.

I have experimented with everything from 100% rock wool to 100% LECA, including 50/50, 25/75 and 75/25 and 1/3 RW/2/3 LECA. I think it's best to see what works for the individual grower, under their own conditions and watering preferences and abilities.

You may be referring to a recent experiment I'm doing with two Maudiae-type paphs - yes, I suppose the mix is about 2/3 LECA, one blended with rock wool mini-cubes, the other arranged in layers. It's too soon to see any difference, but I think that would be a good approach for slippers that tend to put out long, horizontal stolons.

All of my phrags are in S/H culture with 100% LECA.
My paphs are split between that and traditional culture at 50/50, but my phalaenopsis are in 75% RW.

I have no catts at this point, but I'd be inclined to go with 75% LECA for those.


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## spes1959 (Jan 21, 2022)

Ray said:


> There's no "one size fits all" answer.
> 
> I have experimented with everything from 100% rock wool to 100% LECA, including 50/50, 25/75 and 75/25 and 1/3 RW/2/3 LECA. I think it's best to see what works for the individual grower, under their own conditions and watering preferences and abilities.
> 
> ...


Thank you Ray


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## Sky7Bear (Jan 22, 2022)

I agree with Ray about one size not fitting all, as there are many variables, but I think the most important principle to follow is to find the best air/water balance for my own situation. Orchids want adequate of both, and over time this is impossible to do with most organic mixes, as they degrade and change (Orchiata at a slower rate than many others). Terry Root had some of the best Paphs I've ever seen, and he used high-quality bark and still repotted at least once a year, as I recall. 

However, I would add the pot material to the discussion. Plastic doesn't allow for air movement (though holes might help). Alan Koch at Gold Country has excellent success with NZ sphagnum in clay, but with the moss not going all the way to the bottom of the pot. I don't know quite how it happens with clay, but it does appear to "breathe." So perhaps rockwool at the top, an inverted basket at the bottom, and clay.


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## eds (Jan 22, 2022)

Ray said:


> There's no "one size fits all" answer.



Absolutely! 
I've grown my hybrid Phalaenopsis in these glass jars with bark for over 20 years. My wife likes how they look and that they are not going to leak over the windowsill!

I am, however, a chronic underwaterer so they are doing well in spite of me at times! 

I did consider adding another media to the chunks (and have followed your mixing advice with the paphs in pots o am trying) but I can't get LECA the same size as these chunks. I have got some large pumice if this doesn't work on its own but I'm hoping the large size and great voids around the chunks and roots will suffice. There are sections where chunks are side-by-side but plenty of spaces where they aren't.

Basically I think this might work for me with how I grow in my home - we shall see!


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## Ray (Jan 22, 2022)

Sky7Bear said:


> I would add the pot material to the discussion. Plastic doesn't allow for air movement (though holes might help). Alan Koch at Gold Country has excellent success with NZ sphagnum in clay, but with the moss not going all the way to the bottom of the pot. I don't know quite how it happens with clay, but it does appear to "breathe." So perhaps rockwool at the top, an inverted basket at the bottom, and clay.


Certainly container choice is one of the many variables that affect your culture - unglazed clay pots are very porous (speaking as a degreed ceramic engineer and ceramist). Just how much air flow is through the pot I don’t know, as that varies with raw materials and firing, but that porosity “sucks” moisture out of the medium and transfers it to the surface where it evaporates. If the pot stays wet, I suspect there is little air flow, but whether it is due to air flow or moisture transfer, the contained potting medium will dry more more quickly than in a plastic pot. (When used in semi-hydroponics, setting the clay pot of LECA in a tray of water, that evaporation can cool the pot more, helping folks grow cooler-growing plants in warmer environments.)


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## Sky7Bear (Jan 23, 2022)

Thanks for your reply, Ray. Very useful to have a ceramics engineer here. I think I tried one clay pot in S/H. Not even sure where the picture is. Might be useful to experiment more. You have confirmed what I have observed and what I have suspected, and in a sense it confirms what Alan does for his Catts mostly at Gold Country does, and I have observed elsewhere with Phals also. Clay just "breathes" better than plastic, and if I'm not mistaken was the most common way orchids were grown up until WWII at least--probably helped the plants in degraded bark as well. 

So why not rockwool in clay? It occurs to me that the biggest benefit of rockwool is its ability to hold lots of water. Its drawback being possible lack of oxygen. Whether orchids "drown" or asphyxiate is an interesting difference in point of view--it's the same process. In some ways growing in rock wool is just a different "version" of semi-hydroponic except that the reservoir is the wool rather than the reservoir. Or how about just a net pot?

I have also observed that orchids growing in either clay or even a net pot can be kept considerably wetter without apparent damage than the same plant in the same medium in a plastic pot.


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