sub for granite in gritty mix questions

11 years ago

I'm trying to hunt down the ingredients for Al's Gritty Mix for a dwarf Robada apricot tree that I've ordered.
I've been wading through some long threads and keep getting distracted but I'm making progress on finding out what I need and where to look for it. : ) I looked for an FAQ on the mix and didn't find one. Gardenweb has changed their format so if there is one, please link me to it.
I want my container to be light-weight because I need to be able to move it to a sheltered area when we get late frosts/freezes.

Granite sounds heavy so I'm wondering if there's a lighter substitute for that? Not sure I can find granite anyway. If I found foam packing chunks the right size, would that work as a sub? (As long as I make sure they don't disolved in water). Perhaps they would pack down in the mix rather than keep their shape. Bad idea?
I do know where to find poultry grit. Is that lighter or heavier than granite?

Any other tips on keeping it light-weight -or inexpensive? I'm going to try using a large cattle feed container and have also been looking for some kind of dolly to sit it on that doesn't cost more that the tree. : (

Featured Answer

tapla (mid-Michigan, USDA z5b-6a)

11 years ago

Still - because of it's internal porosity, it would be much closer to Turface than granite when being considered as a substitute. The purpose of the granite is to add bulk because of its size, and to act as an mechanism by which water retention can be adjusted by varying the ratio of the highly water retentive ingredient (Turface or other particles with lots of surface area and internal porosity) to the particles with little water retention (granite). So if the substitute for granite has significant water retention, it would be superfluous because it does roughly the same job as Turface.

Comments (8)

MadameMeow
11 years ago
I'm very much a newbie, and others may have better ideas, but I'm trying crushed pumice (Stall-Dry) used for horse bedding. I got a 40# bag for $14; 40# is about 2 cubic feet, maybe more. It is VERY lightweight, like perlite, so you may want to sift out the fines/let the wind carry them off by pouring between 5-gallon buckets. I can lift a "half barrel" size plastic container with tree of 5-1-1 mix without too much trouble- meaning it weighs about...50 pounds I estimate. I used the Turface MVP, used for baseball fields, which I found at Horizon Landscape/irrigation company here in the SF Bay Area. I hope my trees take off in this mix- they are still dormant. In summary- my mix is Turface, bark, and pumice.
Good Luck,
tapla (mid-Michigan, USDA z5b-6a)
11 years ago
What comes closest to being a suitable substitute that will reduce weight is perlite. Stall-Dry is more nearly a substitute for Turface. Though the gritty mix is more than twice ass heavy as peat based mixes when dry, at container capacity (when fully saturated), it's only about 1/3 heavier than most peat-based mixes at container capacity. By substituting perlite for the grit, I'm guessing that you'd reduce the weight of the gritty mix at container capacity by somewhere around 10-15%.

Al
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christie_sw_mo
Original Author
11 years ago
K thanks Al. Maybe I could use a little of both. Depends on what I can find.
That's what I was thinking about the stall dry - that it might absorb water like Turface so your containers may stay too soggy with that mix MadameMeow. Does it soak up water? I need to go by the feed store and see what I can find there.
MadameMeow
11 years ago
Careful, readers; these are 2 VERY different products- DRY-STALL is crushed pumice rock, the other is an absorbent of some kind (don't use that!).
MadameMeow
11 years ago
I wrote Stall-Dry in my post suggesting to use it instead of pumice. I promise you- I just looked at the bag and the correct product name is DRY-Stall
my apologies!
MadameMeow
11 years ago
Your answer made me curious, and since I enjoy an experiment as much as the next gal, I did the following test.
I weighed out 0.5kg of the pumice product - straight out of the bag- into my big spaggetti colander. I wetted it thoroughly under the tap and allowed it to drain for 2 minutes. The weight afer wetting and draining was 0.85kg (including the 150g colander), 0.15kg water was held in 0.5kg pumice.
I did an equivalent test on perlite, noting that the same VOLUME of perlite weighed only 0.25kg, I wetted it and drained for 2 minutes all same. The wetted gross weight was 1.0 kg, ie 0.65kg of water was held in the 0.25kg of perlite.
Hum. this was unexpected.
Now, I'm not saying that pumice does not have more pores, It just doesn't appear that the water gets into them easily. Also, since the mix is defined by volume, it appears, based on this quickie test that the pumice may be a drier though NOT a lighter substitute that the perlite. I couldn't find granite around here, so I can't compare.
Maybe I'll do this again next time I open a bag of turface. I am surprised by the result, frankly.
greenman28 NorCal 7b/8a
11 years ago
The lava rock (Scoria) that I use definitely doesn't hold as much moisture as Perlite. I can see that the pores are much larger and will therefore not hold moisture as well.

Another consideration is particle size. Did you screen the Perlite and the Pumice to the same general diameter? Surface area of small Perlite is going to be a major factor in the experiment if left uncontrolled.

Josh