Rockwool cubes

[Cody]

Where does everyone purchase their rockwool grow cubes? I have a good sized collection of neotropical ericaceae, vireya, orchids and amorphophallus that I'd like to transition to something more sustainable that sphagnum/peat so would need bulk quantities.
For those growing with the cubes; how long do they actually last? What do you do with the spent media? Are you using straight rockwool or adding leca/pumice? Any drawbacks or problems specific to this media?

 

[littlefrog]

I get them at the hydroponics store on the west side of lansing. I just dump the old mix out into low spots in the yard.

I use about 75% bark and 25% rockwool (right now, it varies as I make mix), sometimes I throw spongerok in there if I have it. Main problem is the glass fibers get into my fingers when I repot. I need to remember to wear gloves (black mamba gloves are the best I've found). I am not good at it, I spent last night picking fiberglass out of my little finger since I only potted a few plants.

Personally, I'm experimenting with transitioning away from bark mixes... Using a lot more sphagnum moss (for compots and small seedlings especially phrags). Yes, it is kind of expensive but honestly everything is and I can get a lot more pots out of a big bale of compressed sphag than several big bags of bark - and it keeps better in my barn. Also using a lot of 'promix' high porosity peat based mixes (I prefer sphagnum peat but there are coco-peat ones). If it doesn't look fluffy enough I add perlite until it does. I published a paper in AOS magazine years ago about growing in peat mixes - it isn't new. But it is easier in a lot of ways. Benefit to that is I only have to keep one bale - I can just run out to the hydroponics store and buy more when I need it.

 

[mrhappyrotter]

I usually shop around online and buy from whomever has the least expensive price for the Grodan grow cubes. Sometimes it's Amazon (as much as I dislike using them), sometimes it's not. Don't forget to compare total price including shipping, though usually most places have free shipping over a certain amount, and the cost of the rockwool cubes in bulk is typically enough to qualify.

For example, right now I see a place called HTG Supply has this (https://www.htgsupply.com/products/grodan-grow-cubes-5-cubic-feet-loose-in-box/) for $110.

how long do they actually last? What do you do with the spent media? Are you using straight rockwool or adding leca/pumice? Any drawbacks or problems specific to this media?

Grow cubes last for years. They are inorganic, so they don't really decompose, but over time they do start to break apart and turn into dust. If using them in a completely inorganic media, you can probably go several years or longer between repotting (with caveats). However, in a mixed organic/inorganic media, you might not want to push it past 2.

Spent media goes into my compost bin. Sometimes I reuse it for non-orchids, by mixing it in with soil and then potting up my succulents or bromeliads.

I generally don't use straight rockwool, but some folks do. I usually at least mix in some large grade spongerock. I also frequently use it with bark based mixes.

As for drawbacks/problems, you should definitely soak it first, then check the pH and conductivity of the water to make sure it's "clean" and that the pH is appropriate. Otherwise, you'll need to soak and rinse, as well as use additives to get the pH to something reasonable (i.e. citric acid if too basic, lime if too acidic). You may also need to soak it in a weak fertilizer bath before use. Rinsing also reduces the amount of dust particulates. And on that note, you should definitely avoid inhaling the particulates, so use it in a well ventilated area, outside, and/or use an N95 mask.

Rockwool is a sludge, algae, and invasive fern magnet. It's hard to keep it looking clean and fresh in situations with decent lighting and moist conditions. The sludge and algae look gross and can reduce air flow into the pot. The ferns are mostly a nuisance unless they get really out of hand, but if you don't have those in your collection already then it probably won't be a problem.

Figuring out the feeding rate can be a bit of trial and error. Too little and the plants will develop nutritional issues because the rockwool doesn't provide anything on its own. Too much and the excess builds up quickly in rockwool and can form a crust on the top that's hard to get rid of.

 

[Bob in Albany N.Y.]

Not to hijack this thread but I want to agree that for me a good quality sphagnum moss works very good with plants right out of flask and put into compots. I also want to mention that I'm currently experimenting with a number of new mixes using the New Zealand tree fern. Too early for any conclusions, but at the early stages it appears as if one part tree fern to 2 parts hydroton seems to working out pretty good. However, one must not jump to conclusions as only time will tell. The only problem with using tree fern and hydroton is that you can't just mix up a bucket full at once. The reason being the proportion change greatly between each pot. I only mix one small container of tree fern and two small containers of hydroton into a bucket at a time. It's not really as problematic as one would think. Just have one bucket of each near by and there you go. Am also working with other combinations.

 

[Sky7Bear]

I get them at the hydroponics store on the west side of lansing. I just dump the old mix out into low spots in the yard.

I use about 75% bark and 25% rockwool (right now, it varies as I make mix), sometimes I throw spongerok in there if I have it. Main problem is the glass fibers get into my fingers when I repot. I need to remember to wear gloves (black mamba gloves are the best I've found). I am not good at it, I spent last night picking fiberglass out of my little finger since I only potted a few plants.

Personally, I'm experimenting with transitioning away from bark mixes... Using a lot more sphagnum moss (for compots and small seedlings especially phrags). Yes, it is kind of expensive but honestly everything is and I can get a lot more pots out of a big bale of compressed sphag than several big bags of bark - and it keeps better in my barn. Also using a lot of 'promix' high porosity peat based mixes (I prefer sphagnum peat but there are coco-peat ones). If it doesn't look fluffy enough I add perlite until it does. I published a paper in AOS magazine years ago about growing in peat mixes - it isn't new. But it is easier in a lot of ways. Benefit to that is I only have to keep one bale - I can just run out to the hydroponics store and buy more when I need it.

Hey, Rob, try semi hydroponic. Harvey

 

[southernbelle]

Where does everyone purchase their rockwool grow cubes? I have a good sized collection of neotropical ericaceae, vireya, orchids and amorphophallus that I'd like to transition to something more sustainable that sphagnum/peat so would need bulk quantities.
For those growing with the cubes; how long do they actually last? What do you do with the spent media? Are you using straight rockwool or adding leca/pumice? Any drawbacks or problems specific to this media?

I have ordered them online. They are light, so shipping was not a problem. I have used them on a couple of phrags with about 25% LECA. I don’t see any improvement in growth and don’t like the algae (I grow in clear plastic pots). They are inorganic so never break down. Alll the repots are just “pot ons” when the roots fill the pot, which some like.
Jeff Morris, who grows exhibition phrase in 5 gal plastic pots, uses it and credits it with his success. No root disturbance on repot is something phrags like. He adds about 2” of bark on top of the rockwool in that case to thwart algae. Others on this forum use them so they can give more input.