Correct percentage of sub 1/16" fines in 5-1-1 mix.

10 years ago

I have read extensively on the ingredients used in the 5-1-1 mix especially concerning the task of coming up with the pine bark fines in the correct size range. One thing I have never come across is what would be considered the correct percentage of the PBF's that are included below the 1/16" range or essentially the dust portion of the mix. I realize that everyone tweaks the "base" mix according to the plant being grown and the growing conditions, but is there a general consensus on the base mix particle size percentages? In other words, the percentages of particles between 3/8" to 1/4", between 1/4" to 1/8", between 1/8" to 1/16" and finally below 1/16".

The reason I ask is I buy PBF's by the trailer load and the loads vary wildly in the makeup of particle sizes. The latest load I purchased is almost 40% dust which seems excessive to me, but I am not sure how much of the dust to screen out to reach a more desirable PBF mix to be used in the 5-1-1 mix.

Comments (2)

edweather USDA 9a, HZ 9, Sunset 28
10 years ago
You are fortunate to have the ground pine bark avainable in bulk. Yeah 40% sounds like alot, but to be sure I'd probably screen a known volume and see what it actually is. Not sure if you did that already to come up with your 40% number. I think the recommended amount of fine stuff is 1/6 of the total....that would be about 15% or so.

In my case the 40% wouldn't be too bad, and I might use that as is with a little added perlite. I need an extra part of peat for water retention anyway which would be closer to 30% or so.

Not sure about all the other percentages for the sizes you mentioned. Never really though about it.
spaceman13
10 years ago
I buy mine in 3cf bags and if there is an excessive amount of dust I screen about half with an ordinary window size screen.

I do smaller batches, so it's easy to re-screen some more when finished, or add back some of the "shakins" to adjust the final product.