Pumice, expanded shale, or turface for hot climates?

Chelsea_2016(7b)February 27, 2014

Hi,
I live in Texas with crazy hot, long summers and plan on growing 10 blueberry plants and 6 raspberry plants in Fabric pots. I am worried about the pots drying out incredibly fast even if I water every day and then running into the issues associated with rehydrating a mixture of pine bark, peat moss, and perlite.
So I was considering replacing the perlite with either turface, pumice, or expanded shale if I can find it in less than 3/8" size. I've read if you go higher than a 8:1 ratio of pine bark to turface then growth is impeded and that Turface is also very difficult to rehydrate.

Recommendations for increasing moisture retention?

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nil13(z21 L.A., CA (Mt. Washington))

"... if you go higher than a 8:1 ratio of pine bark to turface then growth is impeded..."

Could you put up a link to that study? I'd like to read it.

Turface definitely rehydrates from a bone dry state more easily than peat, ime. Not floating helps, lol.

    Bookmark   February 27, 2014 at 6:05PM
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Chelsea_2016(7b)

Sure. I got it from another post here about Al's 5-1-1 mix from shazaam:
http://www.ars.usda.gov/research/publications/publications.htm?seq_no_115=184730

    Bookmark   February 27, 2014 at 6:12PM
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greenman28 NorCal 7b/8a

If hydration is your main concern, why use a fabric pot?

I might try a self-watering type system if I were gardening is such a hot region. Pumice or turface will both maintain structural integrity, durability, and water retention in a mix, with turface having the edge. I haven't used expanded shale, so I can't speak to its performance in a mix.

Josh

    Bookmark   February 27, 2014 at 6:49PM
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shazaam(NC 7B)

The nice thing about fabric pots is that you can use heavier mix without the compaction/perched water issues that you encounter in plastic, etc. (as long as the pot has ground contact, that is). So, if you want to increase water retention (and nutrient retention), adding turface is a good idea, but you can also increase the peat fraction, add some coir, or, as I've tried, incorporate some compost and/or soil. I'm adding a few new blueberries in fabric pots this year, and I'm trying out a mix that's 63% aged pine bark fines, 22% peat, 10% NAPA oil absorbent, 5% compost, and 5% soil (clay loam, to be precise). If I were growing them in plastic, I'd stick to the 5-1-1 mix (which has served me well), but fabric gives me more options.

    Bookmark   February 27, 2014 at 7:18PM
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Ohiofem(6a Ohio)

I don't have the climate challenges you do, but I have experienced long spells of temps in the high 90s with no rain. I used 5 parts pine bark fines to 1 part NAPA Floor Dry (product #8822) to 1 part compost to increase water retention in my large smart pots. The NAPA product holds more moisture than Turface. I believe it's pH is closer to neutral than Turface. I never had a problem rehydrating this mix or the standard 5-1-1 that I use in solid containers.

    Bookmark   February 27, 2014 at 10:06PM
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nil13(z21 L.A., CA (Mt. Washington))

Did you read the study or just the abstract?

    Bookmark   February 27, 2014 at 10:08PM
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nil13(z21 L.A., CA (Mt. Washington))

ok, so here is the study. Not to hijack the thread, but let's see who can figure out why they might have seen a growth falloff at 12%.

Here is a link that might be useful: owen 2004 (pdf)

    Bookmark   February 28, 2014 at 12:34AM
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seysonn(8a WA/HZ 1)

BTW: I looked at that study, briefly. In that study they used Oil Dri (DE) not Turface. I think Oil Dri (DE) retains more moisture than Turface. It also indicated that 12%(7:1) was optimum.

I tested water absorption of oil dri(100% DE). It has a 100% by weight absorption. E.g. One pound dry weight will absorb one pound water.

    Bookmark   February 28, 2014 at 4:13AM
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nil13(z21 L.A., CA (Mt. Washington))

That's not it. They used calcined clay from the Oil-Dri corporation, which isn't the same as the DE made by that same corporation.

Anyone else?

    Bookmark   February 28, 2014 at 10:38AM
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shazaam(NC 7B)

I'd guess that particle size was the problem -- the calcined clay that they used was screened to a size range of approximately 0.01" to 0.03".

    Bookmark   February 28, 2014 at 10:53AM
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Ohiofem(6a Ohio)

I read the study, and if you look at the figures at the end you will see that adding any clay (which Turface is) gives better results than no clay. The best results come from 12% or a 7:1 ratio, but even 20% clay or a 4:1 ratio is better than 0% clay. So Turface does not impede growth. Also note that the study is only comparing 100% bark to bark with some clay.

But the OP's question is which amendment is better at increasing water retention without causing problems. Of the three choices offered, I would choose Turface. Other choices that might be more effective would be peat, DE or compost. But too much of any one of them (more than 20%) might cause drainage problems.

    Bookmark   February 28, 2014 at 11:06AM
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nil13(z21 L.A., CA (Mt. Washington))

shazaam wins the prize. They were looking at the addition of sand sized calcined clay as a water retention additive. I would imagine as a substitute for actual sand. Turface is a much coarser calcined clay and as such the calcibed clay used in this study is not analogous.

And this is why you have to carefully read the study and not just the abstract.

:edit: what's really interesting is they were getting the effect of about 30% sand with half the material. And let's remember the reason growers add sand to container media is because it facilitates even wetting of the media. It is not for increased drainage like some people think.

This post was edited by nil13 on Fri, Feb 28, 14 at 12:02

    Bookmark   February 28, 2014 at 11:38AM
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nil13(z21 L.A., CA (Mt. Washington))

Based on the research coming out of Missouri, 40% Turface (they don't screen it) is an upper bound. Now that's with gravel so with pine bark I wouldn't go anywhere near that high. I have had success at 25%.

    Bookmark   February 28, 2014 at 11:54AM
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Chelsea_2016(7b)

Thanks, people. I feel better about using more Turface in my mix, skipping perlite completely. Since I am using a fabric pot I'm not worried about the mix holding too much water. Besides, the "course grade" perlite had a ridiculous amount of powder that I was not looking forward to sifting through :)

    Bookmark   February 28, 2014 at 8:04PM
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shazaam(NC 7B)

I'm curious, Chelsea -- what size and brand of fabric pots are you using?

Thanks for encouraging everyone to take closer look at that study, nil13. I completely glossed over the small particle size when I first read it last year.

    Bookmark   March 1, 2014 at 11:13AM
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Chelsea_2016(7b)

Shazaam,
I'm using 2 black 10 gallon smart pots, 15 7-gallon tan with handles GeoPots, and I just ordered 10 black fabric pots from BountifulPlantPots on Etsy.com 16" x 12" (10 gal) because although I really wanted tan pots with handles, the BPPs were so cheap I couldn't resist. $3.26 per pot!!! The geopots were $7.05 for 7 gal.

    Bookmark   March 1, 2014 at 11:50AM
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shazaam(NC 7B)

Those sound like good choices. I've found that 5 gallon pots dry out much too quickly for my liking, but 10 gallon pots are much more manageable. In the heat of summer, I can get by with watering 10 gallon pots every other day (and that's with the standard 5-1-1 mix).

    Bookmark   March 1, 2014 at 12:57PM
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drew51 SE MI Z5b/6a

If you want to retain the most water use Diatomaceous Earth. Ultrsorb or optisorb are excellent products.
DE seems to hold more water than anything else. Also has a pore size which works well to supply water when needed. Seems turface pores are a little small and hard for plants to access. Pumice is a little too large and gives up water easily. DE seems to be somewhere inbetween.

http://www.sciencedirect.com/science/article/pii/S0341816212001841

http://www.sciencedirect.com/science/article/pii/S0341816211001615

http://scihub.org/ABJNA/PDF/2010/5/ABJNA-1-5-1076-1089.pdf

Here is a link that might be useful: Axis

This post was edited by Drew51 on Wed, Mar 5, 14 at 9:48

    Bookmark   March 5, 2014 at 9:29AM
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