Author Topic: Coal as a top dressing?  (Read 772 times)

InfraDig

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Coal as a top dressing?
« on: May 21, 2022, 22:34:27 »
Yesterday I was looking at a garden that had been top dressed for the winter with coal. I think the idea was that the blackness would help with raising the temperature of the soil. Any thoughts on what the long term effects would be? A good idea?
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Coal as a top dressing?
« on: May 21, 2022, 22:34:27 »

Beersmith

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Re: Coal as a top dressing?
« Reply #1 on: May 21, 2022, 23:42:38 »
It doesn't seem sensible to me.  Coal contains quite a lot of toxic ingredients.  Remember that coal tar and other distillates are the basis of creosote which is really nasty stuff. Obviously as a mineral the bulk of the material is made up of carbon compounds often containing benzene rings and other polyaromatic compounds. My hunch is that this is a bad idea but an interesting question and I'll read further comments with interest.  I'm assuming it would be crushed to some degree.
Not mad, just out to mulch!

pumpkinlover

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Re: Coal as a top dressing?
« Reply #2 on: May 22, 2022, 08:00:23 »

i agree with Beersmith, but would be interested to hear what it looked like?
My instinct is that it would not look nice!



Tee Gee

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Re: Coal as a top dressing?
« Reply #3 on: May 22, 2022, 10:00:12 »
Ditto to the above!

I recall when we had coal/ coke fired heating where I would form footpaths with the resulting ash.

Apart from it giving a good well drained surface to walk on, it it was generally weed free!

I put this down to the toxic chemicals in the ash.

Now I realise that that a chemical reaction will have taken place during the firing process meaning the coal might release more or less toxins as it weathers compared to ash, but to quote an old saying there is no smoke without fire (pardon the pun) my point is…..no weeds.

Meaning as weeds are plants we do not want what, will happen to the plants we do want?


InfraDig

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Re: Coal as a top dressing?
« Reply #4 on: May 22, 2022, 21:41:34 »
A notice said it was a ton of delivered coal. It looked the same as you would expect to use in a fireplace over winter. It was unused and not broken into very small pieces.

Beersmith

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Re: Coal as a top dressing?
« Reply #5 on: May 22, 2022, 22:51:38 »
A notice said it was a ton of delivered coal. It looked the same as you would expect to use in a fireplace over winter. It was unused and not broken into very small pieces.

Well now I am totally confused. A ton of delivered coal would be somewhat less than a cubic metre. If the chunks were very small, say only 5cms thickness on average the coverage would be about 5 by 4 metres.  But how long would it take before it might start to break down? Who knows. But holidays on northern coasts suggest sea coal can roll about for years in the ocean and on sandy beaches in sizeable pieces.

So someone has covered their garden with a 5cm layer of rocks that may be toxic and may take decades to break down. Even if the toxicity was not an issue what is going to grow through a layer of rocks?  Not a wise move I fear.  Please post further updates if you are able.
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Vetivert

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Re: Coal as a top dressing?
« Reply #6 on: May 27, 2022, 12:32:19 »
Any idea whether it is actual coal, or charcoal? Because a surface dressing of the latter wouldn't be a bad idea.

ACE

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Re: Coal as a top dressing?
« Reply #7 on: May 27, 2022, 14:26:16 »
When we used to holiday in the Canary Islands I once went to a botanical gardens. Every plant was mulched in black volcanic chippings. Something to do with trapping night time moisture. Not a lot of point in the winter here though.

Tee Gee

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Re: Coal as a top dressing?
« Reply #8 on: May 27, 2022, 16:10:36 »
Quote
Something to do with trapping nighttime moisture.

I always thought because it was dark, it absorbed heat during the day rather than reflecting it.

This absorption causes a 'storage heater affect' thus making the beneficial heat available during the night.

The nighttime moisture you mention Ace could well have taken the form of condensation and give the benefit you describe.

In terms of coal/coke, and I am not so sure, as I think lava dust might be inert because it has been around for many years and weathered, whereas coal/coke might still be a bit toxic!

I am still out with the jury on this one!

 

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