Volcanic Red Lava Rock as S/H media

[Ray]

You're lucky you have that availability of apparently good material. Some sources of lava rock are loaded with minerals that are toxic to plants, and will slowly kill them.

[Zildjian]

Originally Posted by rodrigo

Wouldn't that be true for any medium? Baked ceramic pellets as well?

Besides, is there a better solvent than pure water for "the accumulation of organic matter and plant wastes"?
If so, I would like to know about it... Maybe I'll stop taking water showers myself

Thanks,

Rodrigo

I read somewhere that limestone would solve the accumulation of salts in lava rock.

[Vanda lover]

I thought that it takes an acid to desolve salts.
I used to have to put vinegar in my dish washer to prevent the minerals from our heavy water in Ontario.
Yesterday I saw houseplants for sale in a Canadian tire store, that are mounted on lava rock. They seemed happy.

[Ray]

The so-called "salts" (they may- or may not be true salts) we see depositing on potting media have three sources:

1. Minerals dissolved in the water supply
2. Minerals added to the water (fertilizers)
3. Plant waste products

As long as the medium stays wet, the various chemicals can stay in solution. As the water evaporates however, the solubility limits of the various dissolved species is reached, and the substances precipitate.

Most water contains carbonates of calcium, magnesium, and iron, and that would make up the majority of minerals deposited from the water alone. Being of alkaline nature, it is those that a low-pH solvent would flush the most efficiently.

Pretty much all of the minerals in fertilizer can precipitate as well, and many of them are acidic in nature, so a lower-pH solvent is less effective at redissolving them.

I don't have a handle on what makes up plant wastes.

[rodrigo]

All I can add to above statement is that to get rid of all that crud, there is nothing better than rain water



Rodrigo

[Vanda lover]

Originally Posted by rodrigo

All I can add to above statement is that to get rid of all that crud, there is nothing better than rain water



Rodrigo

I really have to agree to that! Just flush it good with rain water. We're fortunate where we are now, in that our water comes from melted mountain snow. It has almost no chlorine, the orchids love it and so do we! It's so nice right out of the tap. Our fish like it, too.

Nancy

[Ray]

If you feed dilutely and flush frequently, you will have very slow buildup.

Unfortunately, once you have developed any significant buildup, flushing will not remove it, as the deposited structure is very slow to redissolve.

[Vanda lover]

I've been putting bottles of rainwater in the freezer, because we get very little rain in the summer. It rains like crazy all winter, though. I bought a masdevallia, so I will at least have rain for it. The phrag doesn't seem to mind our tap water. I would like to put it in s/h when I repot it, but there isn't anywhere in town to buy it. I could get volcanic rock here though.

[shadytrake]

I did an experiment with my compots. I used hydroton (a different brand of prime agri) alone, hydroton mixed with arkolite (a locally available diatomaceous rock-not round), and hydroton mixed with arkolite and lava rock (larger chunks-for air movement).

The compots were all of the same plants. (L. purpurata WCL x Mc. brysiana 'Heckler's')

They were all in the same area of the greenhouse under the same lighting condition and watered on the same schedule.

The compots of hydroton and hydroton/arkolite mix have insane growth and are almost ready to put into seedling pots.

The compots with hydroton, arkolite and lava rock slowly went downhill. I lost 5 plants in that compot and none in the others. They have been in the compots since November 2010. I finally removed the seedlings from the lava rock compot last night and repotted them into hydroton mixed with arkolite.

Now this was not a scientific experiment and of course you can expect to lose some seedlings from a flask anyway, but it pretty much confirmed that the local volcanic rock available at Lowe's/Home Depot is not really good material for my compots.

Now I will say that I use this same rock in the very bottom of some of my bigger s/h pots as weight and I don't see any adverse effects on my established orchids. That being said, when I repot those I will be removing the lava rock and I will just use an outer heavy pot to steady the plastic s/h pot if needed.

If the rock you have works for you, definitely go for it. I would like to see photos later on for comparison.

[rodrigo]

Interesting.
Could you provide photographs to illustrate your findings?
Thanks,
Rodrigo