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RE: Soil mix!!

  • Subject: RE: Soil mix!!
  • From: millern@wave.co.nz
  • Date: Wed, 3 Apr 2002 10:36:55 -0600 (CST)

Susan

Here in New Zealand we use pine bark a lot in potting mixes 
(because we have large quantities of it, and peat supplies are 
limited).  We mostly use bark from the Monterey Pine, Pinus 
radiata.   However, it needs processing before it can be used.  The 
following exerpt from an article in 'Begonia News', a local 
publication, by Dr Rod Bieleski, a horticultural scientist, will 
probably tell you more than you ever wanted to know :)

"We take for granted the barkbased potting mix we use today, 
but a lot of research had to go in before it could be reliably 
used. The man who did most of the work was Munoo Prasad 
of the old MAF  (Ministry of Agriculture and Fisheries) Levin 
Horticultural Research Centre, and in the 1980s he spent 
several years in identifying and solving problems. Three 
particular kinds came from using pine bark. It's very low in 
nutrients, has a tot of tannins, and creates too much acid even 
for acidlovers like Camellias. It has to be pre-fed with nitrogen 
 if not, the bark gobbles up all the nitrogen from the fertiliser 
you put on before the plant gets a chance. And it has to be 
mixed with a surprisingly large amount of dolomite lime to keep 
the acidity in check, and to precipitate the tannins. Quite a lot 
goes into making a good mix before it reaches you. There's a 
tot more to it than just mixing up ground bark and pumice sand.

"During the 7 months or so we are growing plants, the mix is 
progressively changing. The bark keeps breaking down and 
releasing small particles, impeding drainage and generating 
more acid. The bark also keeps gobbling up nitrogen. Though 
we apply nutrients in our fertiliser, we aren't providing any 
buffer for the acid. And then we store the bark for 5 months 
until the next season. We've stopped feeding the nutrients, but 
the mix keeps on breaking down, keeps on making acid and 
keeps on sopping up any residual nutrients."

I hope this helps

Nick Miller
On 2 Apr 02, at 16:54, Cooper, Susan L. wrote:

> Can someone explain the pine bark to me?  I've never quite gotten it
> clear in my mind... I thought folks put down pine mulch because
> "something" in the pine bark helps prevent weeds from growing.  The
> explanation given to me was that not much grows in a pine forest
> (except the pines, duh) due to some inhibitor with the pine needles,
> or roots or ???. Am I just totally nuts or has anyone else ever heard
> this?
> 
> If it isn't true I'll start adding a little pine bark to my mix, it is
> easy to find here (up north), people use it for decoration.
> 
> Susan


Nick Miller
Rotorua, New Zealand





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