Shale vs. river stone vs. Lava rock

[Bill Archer]

I'm new here, so not sure if this has been covered or not, and am still working on finding my way around this wonderful site.

But, today, I got the Newsletter, and it commented about using shale as the medium for the garden.  Now, that may be great in the mountains of the west or even up in PA, where we used to live, but we don't see too much of it here on the coast of NC.  So, I wondered about other options that are inexpensive.  I know that Limestone isn't very good, as it will continue to effect pH of the water....and that the riverstone that is common here, may have Limestone in it.  I can get lava stone in bulk, and it seemed to be that all those nooks and crannies in lava rock would kind of do the same thing as the shale, being somewhat porous.

 

Of course, as I think about it, I also realize that at one point in time, we had some of the Lava Rock as a ground cover, and the roots of small plants would grow into the rocks, which became a bit of a hassle too.

 

Would we do better to start off with something like a Pea gravel (granite) that is available from a local mulch dealer, or go with the small river rock?

HERE is a link our local dealer's website, and a list of the various aggregates that they have to offer.  I would welcome your suggestions.

 

As I said, we are just starting off, and we'd like to do it right the first time..   

Thanks in advance for any assistance.

 

Bill & Claudia Archer

Wilmington, NC

 

[TCLynx]

River Rock is often a fine media provided it isn't heavily laden with limestone.  We get a Brown River rock that is fine and is mostly quartz type rocks.  However, the design of your system will affect which size media will work best.  In a timed flood and drain or indexing valve system, the 1/2" size seems fine but in a constant inflow set up with siphons, the 3/4" size will probably be more appropriate.

 

Lava rock is also great, though it is definitely harder on the hands/fingernails when digging in it.  It is important to make sure you are not getting the filter rocks left over from heavy industry through as that could have heavy metals in it.  Lava rock is what the Aussies call scoria by the way.  Lava rock does take a bit of extra washing and I definitely recommend the basket swish method for rinsing lava rock for use in aquaponics.

 

I would do extra research into anything called pea gravel since that only really describes the shape.  Granite would be fine, but like river rock, it's gonna be heavy.

 

The shale I've not tried myself but I know people who have.  It is kinda in-between using local bulk gravel and the clay balls in price.  I've never personally sprung the cash for the more $$ media, Gets really hard to justify when my systems generally need media measured in tons or cubic yards and I can have the local stone supplier deliver a few yards for a few hundred dollars including tax and delivery when most of the fancier options would cost a few thousand dollars.  But for smaller systems, I can certainly see the benefits.  Especially after seeing a video of Sylvia wiggling a plant down into a flooded bed of clay balls and thinking that looks so easy.

 

Anyway, if that local mulch dealer is really local, then I would say stop by and see if they would let you take some samples of the different media you are interested in (take some plastic bags so you can get a hand full of each variety home) Then run some tests on your different choices.  Mainly I'm thinking get a jug of distilled water.  Rinse off each of your samples with tap water and then put it in a container of distilled water.  Wait a few days and then test the pH of the water that the samples are sitting in.  If any of your samples have a high limestone content then you will see the pH of the sample water go up.

 

Another lower tech way to see if any of the rocks is limestone would be using vinegar to see if it fizzes.

[Steve Stark]

Bill,

I am using Pea gravel from Lowes and seems fine so far. I had to initially lower the PH but it has been stable since.

 

Steve

[Bill Archer]

Steve:

Thanks for the information.  I assume that you rinsed the gravel well.  How high was the pH?  I still haven't gotten my system started, so I'm still trying to figure out what goes where...LOL!!

 

Thanks again,

Bill

[Burton]

Has anyone ever done a side by side by many sides comparison of the grow medias in relation to root size?

I know I have seen some youtube videos where people were using unspecified stone and switched to hydroton on several plants and saw a huge increase the the root mass ...

It would be very interesting to see how the weight, size, shape, porosity, and maybe even color affect the end root mass :)

[TCLynx]

Well just because a plant grows more root mass doesn't necessarily mean that is a good thing.  I mean if it is say corn you are growing, it might just be growing more roots in the clay balls because it needs more to hold it up in such a light media.  Other plants that you might be growing for the fruit and not the root might not show any productivity difference between the media though the roots might turn into beasts in one media and stay moderate in another media.  The question of if a bigger root mass is a good thing isn't really addressed.  It has been noted that some plants while possible to grow in hydroponics, tend to grow so much roots that most people give up on them in hydroponics cause they can get just as impressive produce by growing them in compost (like giant pumpkins.)

[Burton]

Interesting point, I wasn't thinking from the proper perspective when wanting to compare the media ...

So then would you suggest a controlled grow where different media are used on the same water and you would test for individual plants and overall size and productivity?

 

The easiest to start with I imagine would be plants which grow fast, like lettuce, and weigh / measure the end product less the root mass. Of course you would probably have to say grow 3 of the same type of lettuce in each media to ensure a good average.

Should we germinate the seeds in the media as well?

I think when I get my system up I am going to try and run some tests for the general public since it will be a very controlled environment. :D

[Steve Stark]

Bill,

My PH was 8.4 or 8.6 something like that but I think it was more my well water and not the pea gravel. Once I got the PH down, it seems very stable so far.

Steve

 

Bill Archer said:

Steve:

Thanks for the information.  I assume that you rinsed the gravel well.  How high was the pH?  I still haven't gotten my system started, so I'm still trying to figure out what goes where...LOL!!

 

Thanks again,

Bill

[TCLynx]

Some controlled tests side by side would be very informative.  Now there are somethings that might not fully show when using the different media in the same system (like if there are any trace nutrients that are coming from one of the media but not the others.)  There are others trying different tests with aquaponics and though small home tests might not be as good as large controlled studies but they are still very helpful.  So please do!

[Bill Archer]

I agree, any study will be better than nothing.  And side by side will have some information that we can all use, so I'm all for it too!

As mentioned, the more things that you can keep the same (same plants, the water source, lighting, etc) the better the result of the test....

 

 

[Burton]

I don't think it will be difficult to keep the lighting, water, and plants the same ... Granted I am not going to go out and get a light meter to make sure each is getting the same lux / par lol ...

 

Yeah TC I dont think I would like to do a test involving identifying which gave X or Y nutrients over the other as it would require a different source of water for each ... someone else who has multiple systems (wink wink) can try that one :)

Just finished wiring the first of my 40 LED lights ... It doesn't have power connectors on it yet but I have a TON of photos. Basically I took two photos every time I soldered something on. Going to go post a teaser now :)

[TCLynx]

aye, but I don't have multiple matching systems at the moment so trying side by side tests for me will have to wait.