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511 / advice needed - how many fines is too many?

Posted by rooftopbklyn none (My Page) on
Fri, Jul 19, 13 at 22:19

First time caller, long time listener. Before my questions, I have to thank everyone on this forum for the huge amount of help they give everyone else. By reading Mr. Tapla's epic threads on Container Culture/Soil and Fertilizer, and a huge amonut of q and a, I've learned a lot and made all of my houseplants very happy.

I've made some gritty mix succesfully with turface, gran-i-grit, and screened reptibark. I'll just note here for anyone reading, that reports on these forums that reptibark is suitable out of the bag for gritty are incorrect. I have tried 4, 8 and 24 quart bags with very consistent results. About 50% is bigger than 1/4" (does not pass a screen). There are also some fines that can be easily dealt with via a colander or window screen. My first batch was made with unscreened reptibark and the amount of bark that was > 1/4" caused bark to migrate to the top of pots, causing excess water retention in the bottom. Moral: screen all bark for gritty mix, unless you've used it before and have a high degree of confidence.

That aside ... I'm now trying to make some 511 for use on my rooftop, where I have about 60 containers of mostly healthy plants in a variety of unhappy soil - but I'm starting to notice the affects and want to repot many things.

I have some pine bark mulch that is somewhat decomposed -- i think, but don't really know because I have no experience to go on. I screened 5 gallons through a 1/12" screen (what I have), and what fell through was mostly dust, or very small pieces. About 1 quart of dust for 5 gallons of mulch. Other than that, it's mostly in the correct size range - not too small, and almost all goes through a 1/2" screen.

Given this, should I modify the amount of peat (1 gallon normally) for 5 gallons of mulch? I do understand the answer depends on the environment, etc, but, lets say, in the "default" case where the normal 511 formulas apply.

If so, should I modify the amount the lime? I would think about 7 tsp of lime for 5 gallons of bark + 1 gallon perlite + 1 gallon peat in the default case - please also confirm this math.


Follow-Up Postings:

RE: 511 / advice needed - how many fines is too many?

Technically if you wanted to make the textbook 511 and you already have 1 qt of fines per 5 gallons of bark, you only need 3 more quarts of fine stuff for the 5:1 ratio. That's kind of splitting hairs though because if you count the mulch fines, you lessen the 5 gallon volume by 1 quart. So IMO, it's nice you have some fines in the mulch, but I'd just add the 1 gallon of peat.

You are correct with the 7, but it's Tablespoons. Not sure if you meant tablespoons, but it looked like you said teaspoons with your tsp abbreviation.

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