Growstone pH rise

[edouard1997]

Hi everyone,

I have 10 phalaenopsis that have been recently repotted into clay pots with pure growstones. I chose growstones as a substitute for Seramis since it's not available in the US because it's inorganic and I don't want to be bothered with organic media breaking down, repotting, etc. They were previously potted in packed and broken down sphagnum moss. I have to say I was skeptical but I took the risk and repotted all 10. They are doing well with ALL 10 growing new roots AND leaves! The only issue I have is the pH of the growstones. I water with rain water and 1/4 strength MSU at every watering (every 4/5 days) which bring the fertilizer solution to a pH of 5. However the runoff water from the bottom of the pots is 8, ive used lemon juice in addition to the already acidic water which seems to help but the media gets basic again over time. Anything else I can do? I just ordered pH down hoping it will keep the pH more stable instead of it becoming basic again.

[estación seca]

I''m not familiar with the product at all. Are you supposed to do anything with it before use? Rinse? Soak?

What is the pH of your pure rain before use, and then the pH of the pour-through with pure rain, pot, existing medium and plant?

What is the pH of the pure rain pour-through with only a pot, fresh medium and no plant?

What is the pH of your pour-through with your standard rain/fertilizer solution after a pour-through with only a pot, fresh medium and no plant?

[katrina]

My personal experience with grow stones was awful. I used it alone and in mixes and most of the orchids lost most (if not all) roots over a year to 2 year period.

I never tested the PH...i just know most hated it. A friend had a very similar experience.

A few orchids liked the media...but it was only a few...a couple of dens, a C Valda, and something else that I can't now remember. All the phals that had it in the mix...lots of root loss.

I stopped using it and gave it all away to someone for use in terrestrial plantings.

[edouard1997]

I've noticed a little of that too katrina, but i'm not worried about it because it was the older roots (probably when it was still a seedling) that died back and a lot more roots are growing. Thanks for your reply!

[katrina]

Hopefully you have better luck than I did.

FWIW- I also used it as filler in the bottom of some pots and in every single pot the roots turned away from it and would not grow down into it like the do with other "fillers". Keep an eye on them!

[Roberta]

In a lecture by Fred Clarke of Sunset Valley Orchids, he discusses problem with use of Orchiata with pure water - the bark is treated with lime to keep it pH neutral, but over time that leaches out and the mix becomes acidic. Roots do not like change of pH over time, so in his case there was root loss because the medium changed from neutral. Here the medium is changing from acidic to alkaline, and likely to lead to a similar effect - loss of new roots. If the medium leaches alkaline when what goes in is slightly acidic it's creating an environment that is unstable - and likely to be detrimental over time. It sounds to me like this medium (which with I am not familiar) is not inert, and probably a bad idea. The stuff is supposedly glass... which is NOT pure silica - has sodium carbonate in it as well. If the sodium carbonate part is leaching because of the way that the original glass was processed (which sounds like what is happening), bad news. Not only is the mix becoming alkaline, it probably is building up significant sodium as well, which is really toxic. Making it acidic may make the problem worse if you're dealing with sodium carbonate.

[Ray]

As a ceramic engineer who was thrilled at the possibility of using glass as a potting medium, I had several conversations with the manufacturer.

It is really nothing more than recycled soda-lime glass to which they add a carbonate to cause it to foam.

Soda-lime glass is chemically basic, and over time the basic ingredients leach out of it. With the high surface area of a foam, that will take place at a more rapid rate than it would in a bottle or sheet of glass.

I don't know if they do it or not, but we discussed "passivating" the surface with acid, after the fact - thereby extracting those basic elements from the surface, rendering it acidic. Whether that is done or not, it's only temporary.

[terryros]

I have used Growstone for about 3 years, but always in a mix with milled sphagnum moss. With a rough experiment, I can see that pure Growstones, even after being thoroughly rinsed multiple times, leach out ions when RO water is put through them. With a starting RO with an EC of 14, the effluent from the Growstone pour through has an EC of about 150 and a pH of about 8.2. I think this is carbonates, maybe both calcium and sodium. Conversely, pure milled sphagnum moss has a pour through EC of about 200 with a pH of about 4.5. As you would guess, a combination of the two (about 60% Growstone, 40% milled sphagnum) has an EC of about 170 and a pH about 7.2.

I use lemon juice with every watering which helps, at least temporarily, with pH control and the citrate and malic acid may have other beneficial effects. In addition, it is likely that you want a fertilizer that still has some ammonium nitrogen in it because this will work with the roots to acidify the potting medium.

I happen to be in a phase of my nutrition cycle where I am using K-Lite at 83 ppm N, lemon juice 5 mL/gallon, MgSO4 1/4 teaspoon/gallon, and Inocucor 15 mL/gallon. The EC of this mixture this morning was 966 and the pH was 4.2. The RO pour through on a spiking Paph Dolliroth this morning (1.5 hours after watering) had an EC of 993 and pH of 6.2. A pour through of a tetraploid Phrag Jason Fischer a day after fertigating still had a pH of 6.5. I am now trying to measure farther out from fertigation to see if the pH holds.

Growstones have some nice properties and I like working with it. I only use Rand Aircone pots. I don't have to water the Growstone/milled sphagnum media more often than once a week, even for Phrags or Miltoniopsis and I can be gone for two weeks without watering anything and have no ill effects. However, I think you do have to be careful with the pH. To use 100% Growstones I think you would not only need to use a good amount of citric acid/lemon juice, but also use a fertilizer high in ammonium nitrate. I think combining Growstones with sphagnum is a better way to go. Using the milled sphagnum moss is much nicer than working with long fiber sphagnum. You could also use some larger Perlite in place of some Growstones to moderate the ion effect.

[Orchid Whisperer]

Seems like a lot of effort needed to keep using growstone as a medium.

Next time you plan to repot, if you want to go with an inorganic medium, try a mix of coarse quartz or granite gravel (1 to 3 cm diameter) and similarly-sized chips of styrofoam. The styrofoam is free if it is from packing material, and the gravel is cheap, possibly even free.

[edouard1997]

Hey everyone, thanks for all your responses! Great ideas! Growstones don't contain any kind of sodium carbonate, it's only calcium carbonate which actually helps in calcium supplementation. I really like using the growstones because it works great with my environment combined with the clay pots. The pH down came today and I did a little experimenting. I mixed a few drops into my fertilizer water to bring it to a pH of 4 and tested the pH of the runoff water at the bottom of the pot of a phal planted in the growstones. The result was a pH of 6! I think a few more waterings of the acidic water and the pH should be stablized. I'll let everyone know in a few weeks. All the phals are continuing to put out new roots and leaves like crazy. Thanks again everyone!