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I'm starting to brain storm some ideas for next year's spring garden projects early and have soil amendments on my brain. Been fighting heavy clay soil in Alberta for years and am gonna stop amending it and just pull it all out and start from scratch.

There are things like bulk garden mix, which I might just use as a control in one bed, but want take a shot at building my own soil recipe. An ingredient that's come up sporadically, but doesn't seem to be widely used is crushed ceramic. A very porous material I'd think it's have great micro pore potential for water retention and mineral ions. My guess is that it's not used very widely because in large quantities it may be hard to find not contaminated with other construction materials.

I've found several people on classified advertisement websites in my area with PALETTES of un used roof tiles that I'm thinking of picking up and giving a go. Would have to crush them myself and will do some other research into the manufacturing process if there's some chemicals present in the ceramic I'm not aware of.

Has anyone here some thoughts on this idea?

I'd be using it in combination with bio-char, peat moss, crushed sea-shells, normal compost, and then the rest some regular "garden mix" from a bulk store locally.

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    Why don't you just plant plants that like living in clay, mulched with wood chips, if you can get them? Alternatively, why not use raised beds? Gardening should never be this hard.
    – Jurp
    Commented Nov 11, 2023 at 0:26
  • Whether it's "very porous" or "not porous at all, like lumps/shards of glass" depends on how it's been fired. This does feel like taking an absurd approach to a "problem" more easily managed.
    – Ecnerwal
    Commented Nov 11, 2023 at 1:12
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    Per the first comment, because I want to grow food instead of ornamental shrubs. Otherwise yes, I do gardening around this area and see things like hostas, ferns, iris's, and some others do well like that. @Ecnerwal, I thought that firing's effect on the resulting texture really only applied to the exterior surface, but when crushed isn't it mostly similar? And about the simplicity part, similar to my other response, yes in most cases just mix some compost in with an existing garden mix; but I'm trying it out partly just to experiment.
    – AustinFoss
    Commented Nov 11, 2023 at 2:35
  • Per your comment of 11/13... I should've answered it sooner. I've very successfully grown the following in clay soil so heavy (it was actually sub-soil) that we did indeed make pottery out of it: tomatoes, peppers, peas, beans, beets, melons, cucumbers, raspberries, blackberries. Mulch was typically hay or cocoa bean hulls. So yes, you can grow plenty of non-root vegetables in heavy clay.
    – Jurp
    Commented Apr 1 at 13:58

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Ceramic has been fired to about 2000°F. It is unlikely to be very porous.

And if it has been glazed, then you don't know what chemicals it has. There are literally 1000s of glazes (my wife is a potter). The glazes may contain chemicals, metals and oxides. Although, unless you are using tens of kilos of it, the chemical levels may be low enough to be harmless.

Note,

  1. When the glaze is intact on top of the ceramic, it is not dangerous to health. However, as soon as you start crushing and pulverizing it, its a different story.
  2. Cheap ceramic mugs, that are mass imported have not been fired at a high enough temperature, which is why the glaze breaks down.
  3. Cheap tiles that are imported are again not fired at a high enough temperature and may be porous. I have experienced the porosity myself. My test is to take a sample tile home, weigh it, dunk it in a pail of water overnight and weigh it again.

Crushed or broken brick may be a better bet.

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You might want to review the experience of a method studied by Cornell University for growing street trees in a mix that can withstand compaction and still allow roots to grow through the medium. Their specific concern is the need for compaction for heavy traffic which is not a concern in your situation, but you might learn some helpful details from the method.

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  • Most interesting to me was "Structural soil less than 24” deep is inadequate for tree growth". Many trees appear to have roots that grow wide but not deep in soil. For their mix deep appears to be the way to go.
    – kevinskio
    Commented Nov 14, 2023 at 15:22
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if you are removing clay soil anyway why not shape it into thin slabs of “pottery” and then fire it in a pit fire situation, thus converting it into a terracotta of sorts and then crush it. Return it to its previous location and go to town inoculating it like you would with Biochar. Add urine, manure, compost, fish emulsion etc. Allow it to marinate, add in your other desired soil components and then plant in it?

I live in Tennessee with the most gorgeous red clay soil that I have minimally processed to obtain shapable clay. I’ve fired it in a standard bonfire and successfully created little pieces of very porous pottery. In your case I don’t see why you would need to process it much or at all to simply create some flat thin slabs that you could burn and experiment with in your garden.

I’m going to try it myself. God speed to you and me!

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  • Welcome to the site! That sounds like a fun project.
    – MackM
    Commented Mar 13 at 13:14
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Yes, as long as it's not made of heavy metals. Baked ceramics used as soil amendments for millennia; see terra preta for an example. However, The broken pottery has to be low fired to be better absorbent. Low-fire ceramics may be crushed and added to the soil; the pieces will act as little sponges, absorb the water, and release it as the soil begins to dry or drain.

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