Gritty mix: substitute granite grit with Marble gravel OK

stefpix(6b NY [Brooklyn NY])May 27, 2011


I have a hard time finding granite grit in Brooklyn. Lowes carries marble gravel and yellowish pea gravel. Could these be a valid substitute for granite grit in the gritty mix?



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Ohiofem(6a Ohio)

The most important thing is size. The stones/gravel/pebbles/grit should be close to 1/8 inch. If you can screen out stuff that's 1/4 inch or bigger and the stuff that passes through an insect screen, and still have a reasonable amount left, you're good to go.

    Bookmark   May 27, 2011 at 10:44PM
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jojosplants(9/ Tucson, Az.)

Hi Stefano,
Like Ohiofem stated, the size is what's important. I was talking with Al recently about how to sift pea gravel because I can't find grit.

Here's a quote from out emails..

" you could keep/use what passes a 3/16" screen but doesn't pass an 1/8" screen."

Finding a 3/16" screen is tricky, i'm still looking for that.
Bonsai screens are in metric, and the closest to the 3/16" would be...
Al said a metric 12/64 = 3/16", the closest I found is a 13/64, so far.

I hope some of this helps.


    Bookmark   May 27, 2011 at 11:21PM
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stefpix(6b NY [Brooklyn NY])

Thanks for the help.
fractional measurements in inches are so counterintuitive. hard to imagine what 13/64 is like and compare without mental calculations! 1/8" is almost 3.5 mm think that gravel is more or less like that. some could be larger, Why is it so important to screen out the larger ones? couln't be an approximation? If a mix is not exaclty the same wouldn't just be sufficient to adjust the watering accordingly?

I also found fine bark at Gowanus nursery but is fine like a slightly coarse soil. Is that way too fine? At HD I found chunkier pine bark.


    Bookmark   May 28, 2011 at 1:22AM
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tapla (mid-MI z5b-6a)

If you have 1 ingredient that varies significantly in size from the others, that ingredient tends to separate from the mix and you're left with a mix that retains the physical properties of the 2 more similar-size components. We want to keep the size range of the particles from just slightly under 1/8" (because that's where the PWT disappears) to about 3/16". The bark can be a little larger to allow for break-down over time. As particle size increases, the soils ability to hold sufficient water decreases. Also, if the bark and grit fractions are large, the Turface tends to settle to the bottom and hold too much water there, so you can see why size is important.

I would skip any marble gravel in the gritty mix because of its high Ca content.


    Bookmark   May 28, 2011 at 11:09AM
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stefpix(6b NY [Brooklyn NY])

Tapla thanks for the reply. Would the pea gravel be OK?

As I said I found fine bark at the Gowanus Nursery as suggested on the thread where to find the materials for the gritty mix. It does not look like wood chips.

Could I mix just Napa Floor-Dry XXX 8822, some bark and some Miracle Grow orchid mix (it is a mix of some peat moss and fine bark, not a real orchid mix but way chunkier than potting soil) and / or perlite? I want to repot my plants on a grittier mix but I can't get huge bags or travel hours. I live in Brooklyn NY. Not much variety in gardening supplies and I live in an apt. I put some plants on the roof and fire escape in the spring / summer/ part fall.

If I can't get the perfect gritty mix I'd like at least have a better mix of what comes prepackaged.

I grow hot peppers (habaneros), ficus, mangos, lychee from seed. Have coffee plants, some tropical aroids.


    Bookmark   May 28, 2011 at 11:27AM
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stefpix(6b NY [Brooklyn NY])

I saw that at the petstore they have silica based gravel and another called spectrastone. They are for fresh water aquariums and the size is right. $3 for 5 pounds. Would that work?


    Bookmark   May 28, 2011 at 3:48PM
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