river gravel for flood/drain

stuiiMarch 9, 2009

Hi Guys,

I was considering usnig river gravdel for my next system to save some money,

my next system will either be a drip from above and drain or a flood then drain system

Does anyone have any experiences growing outdoors using river gravel as a medium?

Regards,

S

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freemangreens(Zone 10 CA)

I used river gravel about 35 years ago in an Ebb-&-Flow system. I found out two things:

First off, it's very heavy. Make sure whatever you fill with it can support its weight wet!

Second: You get more than you bargained for if it has not been cleaned first with live steam. The steam kills all the little "wee-beasties" hiding in the nooks and crannies of the rock. If you use it without cleaning it somehow, your major crop will be algae! It comes on rather fast, by the way, since it holds nutrient-laden water on the surface exposed to light.

    Bookmark   March 10, 2009 at 12:41AM
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greystoke(South Africa(11))

The medium should retain some moisture. So, mix the gravel with saw dust on a 1:1 volume basis. Beware! saw dust compacts a lot.
My mixture is wood shavings (I just buy a suitable plank, then stick it through the motorised planer and collect all the shavings)
First I let the shavings soak a few days replacing the water every day, then I cover them with a layer of gravel to keep the shavings in place, and away we go!

    Bookmark   March 10, 2009 at 12:44AM
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stuii

thanks for the feedback guys..

perhaps before I go and get the river graevl then... can anyone think of a cheap effective re-useable alternative to hydroton (clay beads) for this kind of system?

Regards,
S

    Bookmark   March 10, 2009 at 11:44PM
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greystoke(South Africa(11))

I have used chopped-up baked clay bricks, but its one heck of a mission to make.
They work well though.

    Bookmark   March 11, 2009 at 12:47AM
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freemangreens(Zone 10 CA)

"Perlite"
It comes in three grades; stay away from the fine, powdery one. It's cheap (I pay $14 for a 5 cu. ft. bag) and it's reusable. I soak mine in 30% hydrogen peroxide when I reuse it.

    Bookmark   March 11, 2009 at 12:57AM
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grizzman

I've used river gravel by itself without any problems.
I've also used landscape lava rock and perlite.
With flood and drain I had problems with the perlite getting into the reservoir even with screens covering all points of egress. stick with the gravel or lava rock. you don't have to add anything else, but you may need to increase the frequency of flood cycles.

    Bookmark   March 11, 2009 at 7:06AM
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stuii

thanks guys - I might try to see if there are any good cheap sources of perlite nearby

    Bookmark   March 11, 2009 at 6:38PM
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freemangreens(Zone 10 CA)

Try a farm supply store. They sell it as a soil additive to increase the soils porosity. Be sure to ask which grade it is. Like I said earlier; stay away from the fine, powdery stuff as it will just clog things up. I pay $14 for a 5 cubic foot bag in California.

    Bookmark   March 12, 2009 at 12:40AM
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stuii

thanks freemangreens
I think there is a farm supply shop near me actually

one final question - roughly how heavy and harsh edged is the landscaping lava rocks?

    Bookmark   March 12, 2009 at 5:33PM
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garysgarden

Other similar options include aquarium (fish tank) gravel, marbles, and stuff like that. A mix of perlite and vermiculite works well, as does straight perlite.

My only dislike of perlite is how light it is - it practically floats. That and you have to be really careful about dust. The dust off that stuff can be murder on the lungs.

    Bookmark   March 12, 2009 at 9:12PM
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freemangreens(Zone 10 CA)

garysgarden

Just a quick note of encouragement here: My perlite comes with an MSDS attached and it says pretty much what you said about murdering your lungs, but the other side of that coin is, there is nothing else harmful in it.

Perlite does contain a modicum of phosphorus, fyi.

stuii:

"one final question - roughly how heavy and harsh edged is the landscaping lava rocks?"
Just hop down to Home Depot and take a look. It's lighter than gravel and sharp enough that you wouldn't want to walk barefoot on it, but other than that it's pretty subjective.

As far as it floating away, I water/feed ONLY what the plants use. If you "puddle" as you water, perlite is a nightmare!

    Bookmark   March 13, 2009 at 12:10AM
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eurotrash

I'm currently building an Ebb and Flood system using 55 gallon plastic barrels cut into three (and discarding the middle section and using the top/bottom pieces as separate hoppers for the medium. Another smaller barrel acts as the reservoir, etc.)

For the medium I'm using recycled lava rock from an old fast food restaurant garden bed. That stuff is very light in comparison to river gravel (with maybe 5% of it floating as it soaks it in bleach solution - I've still got a few cleaning cycles to go through). I like working with it as it's got a lot of surface area, retains a good deal of water and is light enough to work with without the need for industrial strength supports for the hydroponics.

    Bookmark   March 13, 2009 at 1:31PM
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willardb3

Commercially available expanded clay pellets are not that expensive and fit the bill for hydro to a tee which is why they are used so much.

Check your supplier's prices on the web. Even the high-priced stuff id $1.50/lb and it lasts forever.

    Bookmark   March 14, 2009 at 10:55AM
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garysgarden

Good point willard. It's a bit of an up-front expense but so is most everything else in the hydroponics world.

And like you say, it's not really that expensive. I've got hydroton I've had forever that's still just as good as when I bought it. Buy the best you can afford and you'll rarely be disappointed, that's my philosophy.

    Bookmark   March 19, 2009 at 6:17PM
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karenrei

In case anyone's curious why one fine-grained thing, like asbestos, can be so harmful, while another, like perlite, can be irritating but otherwise inert, check out their microscopic structures:

Asbestos:

Perlite:

Perlite has a fascinating look to it under the microscope, doesn't it? :) The fine-grained flakes at the bottom of the picture are bentonite clay, and the roughly spherical shape is an undamaged grain of perlite, while the rest are all broken perlite particles.

    Bookmark   March 19, 2009 at 6:37PM
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disinmtl

Thanks for the pic, that is cool. I have a question and some feedback, is there any truth to the "rumour" that vermiculite may contain asbestos?

Also, I have had problems with perlite and vermiculite mixtures, they break down until they inhibit flow/draining, vermiculite more so but perlite does it too. Does anyone else find this? The lava rocks are three bucks for 2'x2'x2" coverage at hd/lowes!

    Bookmark   March 20, 2009 at 4:52PM
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karenrei

is there any truth to the "rumour" that vermiculite may contain asbestos?

There's some truth to it. Vermiculite is often (although not always) found with another mineral called diopside. In the right geological conditions, diopside can turn to asbestos. So, in some mines, the vermiculite is mixed in with harmless diopside, and in some of those mines, the diopside is partially or fully converted to asbestos. In the olden days, they didn't use to check much for asbestos, and some significantly asbestos-contaminated vermiculite products were on the market -- the classic example being vermiculite from the Libby mine that's led to so many lawsuits (sold under the brand name Zonolite). Nowadays, though, it's all checked; the EPA mandates a 1% cap on maximum asbestos content, and it's generally an immeasurably small quantity in vermiculite (esp. in non-dusty vermiculite products). Plus, asbestos is mostly inert when wet anyways; it's when it's aerosolized that it's a problem.

There's risk in almost everything in this world, but the risk from modern vermiculite is pretty low.

    Bookmark   March 20, 2009 at 7:39PM
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stuii

Guys thanks for all of the info - I found a local perlite supplier $20 for 100L

I'm giving that a go in one of by beds...

But for future reference - does anyone know where I can get clay pellets for cheap? the only place I know near(ish) to me is $40 for 45L

    Bookmark   March 24, 2009 at 6:58PM
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garysgarden

I know that perlite can damage the lungs. It's not as bad as asbestos but if memory serves it's definitely more insidious than merely being an irritant.

Whatever the case, it's simple to avoid. Wet it down and there's no danger.

Not sure on cheap clay pellets. I don't use very much myself and since it's pretty much endlessly reusable I don't buy it often. I also don't need enough to concern myself that much with finding the rock-bottom price.

    Bookmark   March 25, 2009 at 11:54PM
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karenrei

I know that perlite can damage the lungs. It's not as bad as asbestos but if memory serves it's definitely more insidious than merely being an irritant.

Perlite is federally classified as a "nuisance dust". Nothing more. It's a lung and eye irritant, but isn't carcinogenic or cause degenerative conditions, as does asbestos. Studies of even perlite *workers* show no evidence of silicosis or other lung disease.

    Bookmark   March 30, 2009 at 7:20PM
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garysgarden

Looks like I was wrong. Cool. Good to know.

    Bookmark   April 2, 2009 at 5:28PM
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