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bark size affecting PWT and drainage

Posted by terratoma 7a (My Page) on
Sun, May 26, 13 at 12:31

There have been suggestions that, to eliminate a PWT and maximize drainage and aeration, the particle size for the ingredients making up the gritty mix should be (1) uniform and (2) no smaller than 1/8", (Turface is often screened to 1/16" to maximize its use.) Has anyone successfully dealt with bark that is too large?

I have lots (and lots) of excess fir bark: it's larger than 1/4" and smaller than 1/2". Thanks to info in an earlier post, I have located and ordered a 3/8" sieve. Somewhere I read that, in certain conditions, the range for bark could be expanded to 1/8"-3/8". Is this range appropriate for fir bark in the gritty mix?
Even if it is, I'll still have much fir bark greater than 3/8". Are there any adjustments I can make, either to the particle size of the Turface and grit or to the ratio of the three ingredients, and still have a low or non-existent PWT and effective (very good) drainage and aeration?


Follow-Up Postings:

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RE: bark size affecting PWT and drainage

Well, you can use that larger bark of Orchids, Hoyas, and Jungle Cacti.

With Fir bark, 1/8 - 1/4 inch is the optimum range.
With Pine bark, 1/8 - 3/8 is sometimes workable, given the flat nature of the Pine bark pieces. Fir does not have the same shape.

From my perspective, the way to make the larger bark work is to increase the size of *all* the ingredients. That will make for incredible drainage...basically, too much drainage. This would then require a larger container to hold moisture, and more frequent watering/fertilization.

In other words, I wouldn't do it.

Josh


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RE: bark size affecting PWT and drainage

Ditto.


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RE: bark size affecting PWT and drainage

Josh and ed
I appreciate the advice. The last thing desired, given what I've experienced with the first batch of mix, is more drainage. :)
I'm assuming that the grit (Gran-I-Grit), like the fir bark, should be screened at 1/4"-1/8". I believe Al recommended that, if you were going to screen the Turface at 1/16" (in order to utilize more of it), you should keep the other two ingredients at 1/4"-1/8". The drainage characteristics would be more influenced by the bark and grit because of their similar size, surface area, etc. (I didn't explain that very well. If I'm wrong about this, let me know.)

Just to stretch my understanding, what if a grower used both Turface and grit screened to 1/16" and the fir bark at 1/4"-1/8"? The drainage characteristics would be more influenced by the smaller size ingredients, right? Would this result in a higher PWT and more water retention? Assuming a grower does not mind frequent watering, are there any situations (specific plants, temperature, etc.) where such a mix would be "good" for the plant? I'm assuming "not", but this is one way to learn.


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RE: bark size affecting PWT and drainage

Hello!
The overall mix will take on the drainage characteristics of the smallest particles because those particles will migrate and lodge in the spaces betwixt the larger particles.

In your second question, yes the mix will retain more moisture and support a higher perched water table. I'm sure there are some plants that would grow just fine in such a mix, but I won't hazard a guess.

Josh


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RE: bark size affecting PWT and drainage

Thanks Josh
The five Japanese maples purchased last fall have been in my first batch of gritty mix for about five days. Three are pitiful _ leaves crinkled and dried _ but the stems are showing green inside. Probably waited too long to root prune: they were fully leafed out. The remaining two are doing just fine.
Took your advice and made the next batch with Turface screened to 1/16" while keeping the bark/grit to 1/4"-1/8". Three of the next five, purchased last week and all much smaller (18" tall), were planted in this new mix this morning. Am looking forward to a bit more water retention.

The question now is the immediate care of the trees after planting. (I search and find the questions and answers I'm looking for. Not writing it down, by the time I'm ready to make the mix, root prune, plant, etc., I've forgotten not only what I've read but where I found it. At my age, relying on memory is not the most reliable mechanism.)
I "think" I recall something about keeping them out of the sun, and withholding fertilizer, for the first few days. Just keep them moist. Then, gradually, begin exposure to the sun and weak fertilizer at every watering.
Is this in the ballpark?


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