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

rooftopbklynJuly 19, 2013

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.


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edweather(Zone 5a/b Central NY)

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.

    Bookmark   July 20, 2013 at 12:18AM
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