Growstones

[brandohobbit89]

[youtube]http://youtu.be/c_CnBghPc60[/youtube]Anyone head about these? They're made from recycled glass into these pumice-like rock sponges basically. There are two different types.. Large rocks used for hydroponics mostly and smaller pebbles used for soil aeration. How do you all think these would do in a cactus mix in place of perlite? Could you even just do a mix of just soil and these stones? The rocks can act as a sort of time release water system because of the way they soak up water and slowly let it out. There are other videos showing roots clinging to the rocks with really healthy plants. Hell, could you even put a cactus in a pot of stones and just have to give it a fertilizer often? I know that's a crazy idea but it might work, yes no?

[Saxicola]

Basically it looks like they are charging a premium for what is essentially man made pumice. If they have a fine enough form (ideally around 5-10mm) then it would work just fine. But I can get actual pumice for a reasonable price.

I grow most of my plants in pure pumice. They tend to do great in it, but you have to fertilize every time you water because it doesn't hold onto nutrients very well. The same thing would apply with this stuff.

[CactusFanDan]

Perlite is horrible stuff, try to avoid it. As Saxicola says, that stuff's essentially pumice. It seems quite expensive from what I saw on the website. It'll have basically the same properties as hard-fired molar clay or pumice, one of which you're bound to find for a lower price than that stuff.

[brandohobbit89]

Ah very good then! So pumice and that hard-fired molar clay is basically the same stuff. Would you be able to germinate in a "soil" of nothing but one of those substrates? What size would be best? I see there are 1/16" up to 3/8" and larger. I'm asking for the sake of cacti cultivation.

[greenknight]

Sure, you can plant seeds in a pure mineral medium. After the cactus plants have been growing for a month or so you'll need to give them some dilute fertilizer, since it contains none - but many people use that method successfully.

[brandohobbit89]

Wow that's really amazing! What's a good fertilizer that cacti like?

[DaveW]

I would think the Growstones being made from recycled glass would be pretty well chemically inert, therefore just alter the potting mix texture rather like gravel, though of course some types of gravel could slowly provide limited nutrients as acids in the soil slowly dissolve them out. Whereas pumice would provide some nutrients since plants can start growing on lava flows once they cool down so must be obtaining some nutrients from it:-

http://www.arkive.org/lava-cactus/brach ... 32725.html" onclick="window.open(this.href);return false;

"The chemical properties of pumice will vary from deposit to deposit, but essentially, pumice is primarily Silicon Dioxide (Amorphous Aluminum Silicate), some Aluminum Oxide, and trace amounts of other oxides."

"Pumice is a rock, not a chemical component, so it can have a range of chemical compositions, but will always contain O, Si, Al, K/Na, Ca, Mg/Fe, roughly in that order (high to low), as well as a variety of trace elements. It chemically weathers into clay minerals and quartz, making some nutrients available.

Generally, if you get a darker volcanic rock, it has more Ca, Mg, and Fe relative to K and Na--in igneous systems, Ca and Mg/Fe-rich minerals crystallize at higher temperatures than K/Na-rich minerals and produce darker rocks. Those minerals are somewhat less stable at the low-temperature/low-pressure conditions that we're used to, so they will weather more quickly than lighter-colored volcanic rocks into clay minerals and quartz. Again, it is probably not at a rate that matters much."

Evidently the grade of pumice used can affect plant growth and water retention in pots:-

http://hortsci.ashspublications.org/con ... /1274.full" onclick="window.open(this.href);return false;

[Saxicola]

I would think the Growstones being made from recycled glass would be pretty well chemically inert

Probably, but I was a little concerned when they said in the video that it is 98% glass and 2% calcium carbonate (limestone). I don't know enough about the chemistry of this to know what happens in the production process, but I'd at least want to make sure the end product wasn't too basic.

I will say this for the product, if it is as similar to pumice as it sounds (notwithstanding the differences Dave pointed out) it might make a good substitute for pumice in regions where pumice is hard to get. Here in California we have a huge deposit that is mined out in the desert, but in a lot of areas of the US and Europe it is very hard to come by. Maybe if this is successful it will become readily available (and cheaper) than it is now.

[greenknight]

Wow that's really amazing! What's a good fertilizer that cacti like?

Any liquid "bloom food" type formulation (low N, higher P and K), mixed at no more than half strength. I've been using up some African violet fertilizer I had left over after cyclamen mites killed all the African violets.