Pros and Cons of Grodan rock wool mini cubes

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Bob in Albany N.Y.

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I've been hearing about these for sometime now. Was hoping that members here can share their experences with this media. Want to hear both the good and the bad. Please be sure to include your growing conditions and locations. Such things as, can you pot up without removing the cubes? Does the roots grow threw the cubes. Can the cubes be reused. Do they hold salts? What group of orchids are you using it for? How often does it need to be changed, once a year? How often do they need to be watered in your conditions? Do you need to still sit them in an inch or two of water for phrags?

Thanks to all members that take the time to inform the rest of the members on this forum.
 

Duck Slipper

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I have used gro cubes as a part of a potting mix...I have used it as a mix with gro cubes and perlite. Currently a kovachii and a Fritz Schomberg potted up in cube/perlite mixture.
Yes the roots kind of attach or grow through it but it doesn’t really matter because it doesn’t decompose. I have never reused it, but a plant can stay wetter longer in it, before repotting. In fact, probably considerably longer.
It definitely has benefits and unique abilities as a potting media.
 

abax

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In my very humid greenhouse growing conditions, I get any Phrag.
that's in Grodan out as quickly as possible. It stays too wet too long.
 

monocotman

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Whereas in my indoor conditions with much lower humidity than Angela, it is an amazing medium for phrags. I water the plants about once a week when the water in the trays has dried out,
David
 

southernbelle

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I've been hearing about these for sometime now. Was hoping that members here can share their experences with this media. Want to hear both the good and the bad. Please be sure to include your growing conditions and locations. Such things as, can you pot up without removing the cubes? Does the roots grow threw the cubes. Can the cubes be reused. Do they hold salts? What group of orchids are you using it for? How often does it need to be changed, once a year? How often do they need to be watered in your conditions? Do you need to still sit them in an inch or two of water for phrags?

Thanks to all members that take the time to inform the rest of the members on this forum.
Jerry Fischer at Orchids,Ltd. says phrags and miltoniopsis love the grow cubes. His mix is 65% cubes, 25% perlite, 10% charcoal. I use 55/35/10 and next mix will add oyster shell. He also uses bark for phrags, but not moss, as he says it tends to be too acidic. I now grow phrags and miltoniopsis in my main level of my home high 74 day temps with air circulation, 45-50% humidity, very bright East windows, because my grow room (under LED lights) was too warm for them to be happy at 84 degrees in summer.

I water when the cubes on the surface just start to dry (phrags). The cubes, according to the manufacturer are 50% hydrophilic and 50% hydrophobic, so technically hold ½ air. Jerry says their shape causes good air spaces in the mix, especially with the perlite. 7 days is a little long for me to go, but my phrags are in small pots being rehabilitated, right now. I feel as though they stay wet, as the cubes do not dry out visibly below the surface, but there is good root growth with them (I use clear plastic).

If you search a previous thread I started in April/May "Advice, please re Phrags", if my memory serves me, PeteM posted pics of a small Fritz Schomberg he bought at the Paph Forum the same day I bought one. These were not well rooted. I downsized mine which was in bark, to bark, he downsized his experimenting with grow cubes mix. His results after just a few months were remarkable per his photo--I almost lost mine!! I've since repotted in grow cubes and moved it to cooler temps.

Re repotting without removing the cubes. Yes, according to Jeff Morris of Charlottesville Orchid Soc. who exhibits many CCM awarded specimen phrags (many of the same plants get CCMs every year he exhibits) in large (2 gal and larger containers) because the cubes never break down, he just removes the pot, puts it in a bigger pot, adds cubes around the outside/bottom and (in large pots) adds a couple of inches of bark on top to keep algae from growing. His theory is phrags don't like their roots disturbed, so they are very happy with this system and his plants certainly are a testimony to that!

Re accumulating salts, yes, so every 3-4 weeks flush with clean water, no fertilizer (per Jerry). So the last week of the month, they get clean water. I do not sit my phrags in an inch or two of water. Some do, but it has never worked for me (I killed my first Jason Fischer doing that when I went away for 4 days, it was still moist when I returned, however, declined rapidly after that.) I've not noticed my roots growing through the cubes, but I see a lot on the outside of the mix through my clear pots, but I don't pick apart the mix when repotting, so they might. Hope this helps. Look up the thread, a lot of comments there will be helpful and Pete M's photos speak for themselves!
 

PeteM

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I'm still experimenting with these, I have yet to get through an entire growing season. I have seen strong root growth in young and or rootless phrags transferred from bark mixes, this was in winter and spring during cooler conditions in my grow area. Currently I am cycling to a warmer night time low and many of my phrags have slowed down a bit. So I have not transferred additional phrags to the cubes.

Two of my phrag divisions of 'Spot On' are in the cubes (repotted in the winter) and are currently still blooming.. but have looked a bit stressed, I believe it's the higher temp and increased light from the position on the grow bench. The leaves were yellowing (very light light green all over) a bit, so I just moved them to a lower light and cooler grow environment next to the evaporative cooler (another experiment). It also might be the grow cubes needing to be replaced. I have not repotted any of my plants that are in grow cubes yet, I was hoping to get through the summer.

Other orchids that are thriving right now in grow cubes / perlite mix. THRIVING. Catasetum, have come out of their dormancy this spring and taking up large amounts of water, root growth is strong in aircone pots. Habenaria, have also come out of dormancy and are thriving in the cubes. I would say, any orchid that needs large amounts of water during it's growth cycle would be a good candidate. If I remember to get some pictures I will post. Hope this helps.

Pros: relatively affordable, available in the states form hydroponic stores in large quantities for close to $40 for a very large bag. Very light weight, so might be less expensive to ship if you need to. Inorganic, running it a bit wet for a bit longer without rot issues maybe possible. I plan to use it to replace all my sphagnum moss.

Cons: wet it before you use it as some of the information I found has it as an irritant for people with allergy sensitivities. Also wear thick gloves when working with it. I have found thin nitrile gloves are not thick enough and I still feel the rockwool on the back sides of my hands, I do use the back sides of my fingers sometimes when tapering down during repotting. Nothing big, just a slight scratching. Salt accumulation? TBD. I fertilize almost every day with a hand pump spray at the roots at very low levels of PPM (50). I run RO water and flush with RO hose about 15 minutes after spraying. I also have been experimenting with growdan cubes and phrags in net pots (kovachii). So far so good. once I get into the next cooler growing cycle I should have more results on this front.

added some images below. I should also mention I use a heavy layer of styrofoam peanuts at the bottom of all my pots. This might also change depending on results.

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KateL

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I have been using the Grodan cubes for 1/2 of my slightly bigger kovachii seedlings. The others are in sphagnum. They are under shade cloth, open to rain, as well as frequent watering in a climate that is undoubtedly too warm to be ideal. I sprinkle the media liberally with oyster shells and dolomite to keep the pH up a bit. I haven’t killed them all, so that’s a plus. I haven’t grown any to blooming size yet either, although I have a couple that might be getting there. I have not drawn a conclusion yet on the media. So far, the sphagnum seems to be as good as the cubes, as long as I keep it relatively fresh. I am thinking about trying to plant them shallower and flatter (maybe like Tom K’s tray method, if I can find something that works), as the last one I repotted (from cubes to cubes) had all of roots right near the surface. Going to check out a couple more before I decide it’s a pattern.
 

Silverwhisp

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I am thinking about trying to plant them shallower and flatter (maybe like Tom K’s tray method, if I can find something that works), as the last one I repotted (from cubes to cubes) had all of roots right near the surface. Going to check out a couple more before I decide it’s a pattern.
Kate— What has worked for me are bulb pans (“Plant Pie“ trademark), and bonsai forest trays, from eBay seller takashima_bonsai.
 

PeteM

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I have added a significant amount of styrofoam peanuts to the bottom of many of my larger pots to simulate this reduction in pot size and then you can adjust the depth accordingly by plant.
 
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KateL

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Kate— What has worked for me are bulb pans (“Plant Pie“ trademark), and bonsai forest trays, from eBay seller takashima_bonsai.
Thanks, Patricia! I just ordered a couple to try!!
 

Silverwhisp

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Great! The bonsai trays have a gazillion holes.... Right now I’m using a bulb pan for my adult besseae- it’s got pretty good drainage, too.
 

Tony

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I use them with perlite and or LECA for nearly everything and love them. I can water every day during the hot South Carolina summer without having to worry about rotting roots. Here are some roths seedlings one year apart:
 

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Linus_Cello

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I use them with perlite and or LECA for nearly everything and love them. I can water every day during the hot South Carolina summer without having to worry about rotting roots. Here are some roths seedlings one year apart:
What is your winter culture for the Roths? Do you have a GH or windowsill?
 

Duck Slipper

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I have some Phrags in a 4 parts Orchiata, 1 part charcoal, 1 part perlite, 1 part cubes for two years now. The cubes hold more moisture and the Orchiata takes longer to break down...All others, Paphs. and Catts. are in 4 parts Kiwi bark, 1 part charcoal, 1 part perlite. I ordered a good sized bag of cubes from Amazon.
 

tomp

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Kate— What has worked for me are bulb pans (“Plant Pie“ trademark), and bonsai forest trays, from eBay seller takashima_bonsai.
Just looked at the “plant pie” info and they look like an interesting concept. Could you please say more about what you might or would or would not use these for. Thanks
 

southernbelle

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I use them with perlite and or LECA for nearly everything and love them. I can water every day during the hot South Carolina summer without having to worry about rotting roots. Here are some roths seedlings one year apart:
What % perlite in the mix?
 

Silverwhisp

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Just looked at the “plant pie” info and they look like an interesting concept. Could you please say more about what you might or would or would not use these for. Thanks
Right now I’ve got an adult Phrag. besseae in one. It’s very happy. If my Mexipediums ever take off, i.e. , multiple spreading growths, I might consider using a Plant Pie for them.
 

PeteM

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I use them with perlite and or LECA for nearly everything and love them. I can water every day during the hot South Carolina summer without having to worry about rotting roots. Here are some roths seedlings one year apart:
thanks for the pictures and info.

How often do you find you need to repot with this mix? Maybe you already have a system to repot every year or sooner? I’m curious to see what Interval has worked best for phrags, paphs, other orchids if you have any in the same mix.

Is there anything specific that you look for to indicate that the mix has deteriorated and you need to repot?

Are there any other recommendations, like things to Absolutely avoid When using this mix, that might have led to unfavorable results? Thanks!
 
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