Green Sand?

sfg_newbie(6)October 1, 2007

I was browsing the garden supply area of my local hardware store this weekend and noticed a giant bag of something called "green sand". Has anyone heard of it, and/or know what it does? There were no instructions or anything on the bag, just the name and weight. It sounds intriguing!

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Greensand is a material used as a potassium fertilizer. I am surprised that there is no N-P-K info on the bag.

    Bookmark   October 1, 2007 at 12:24PM
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I may be wrong, but I think that the law in the US is that if something is sold as a fertilizer, it must list the NPK, but if it's sold as an amendment, it doesn't need to list them. So if it's being sold as an amendment, it would not list the NPK. Espoma lists the NPK as 0-0-0.1.

In addition to the potash, it also provides iron. Greensand isn't available here, but my understanding is that the iron is in a form that is available to plants in alkaline soils that often inhibit the uptake of iron.

    Bookmark   October 1, 2007 at 12:56PM
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gardenfanatic(MO zone5b)

Greensand also helps drainage in clay soil.

    Bookmark   October 1, 2007 at 5:48PM
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paulns(NS zone 6a)

This has always interested me because there is an exposed layer of greensand (also known as 'marl') down the road from us, but I don't know the landowner and besides, getting some would involve bushwhacking and a shovel and pick. Canadian Organic Growers website says:

Greensand is an excellent source of potash which becomes
available slowly. Greensand marl has a high moisture-holding capacity and is rich in
trace elements due to its origin in the sea. It is difficult to find a source of supply. Feed
stores, garden centres, nurseries or even hardware stores may be able to get it for you.

Key words are 'available slowly'. And you should have a soil test to check your potassium levels before considering it.

    Bookmark   October 1, 2007 at 6:13PM
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dchall_san_antonio(8 San Antonio)

Look up 'glauconite' for more information.

My understanding is that the iron in green sand is not available; however, through some chemical or biological methods, iron that was already in the soil does become available.

    Bookmark   October 2, 2007 at 12:05AM
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the_virginian(Zone 7 NoVA)

If you have red clay soil like I do, there is plenty of iron in the soil. Greensand may help free some of it, but more organic matter seems to improve my soil more.

    Bookmark   October 2, 2007 at 4:31PM
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diggity_ma(5 MA)

It actually brings up an interesting question - in what form do plants use iron? If I remember correctly, greensand is an oxidizer, and will precipitate out ferric iron (ferric hydroxide I think) from the WATER - not necessarily from the soil per se, as this is an aqueous reaction. As a matter of fact, greensand is used in to remove iron from residential water supplies. It oxidizes ferrous iron to ferric, which can then be filtered out. So does this mean plants can use ferric iron (rust) better than the soluble form?


    Bookmark   October 2, 2007 at 4:41PM
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