At 09:31 PM 11/14/03 -0500, Chris Cochrane wrote:

I know fresh wood chips draw nitrogen from the soil (bad for plant growth)
and assumed freshly-stripped bark (not necessarily the exfoliating outer
layers) would also draw nitrogen from the soil. The composted bark I've
seen bagged is still pretty fresh (maybe too fresh) when sold at the
building supply stores in central Virginia. I imagine "composted" is
marketed like aged fine wine, but not closely regulated.

Chris

I don't believe there is a 'too fresh' state for using bark. I use bark
that is uncomposted and in fact still aromatic, the same bark that orchid
growers use. Nina has posted about this before too. Some of the compounds
in fresh bark may even have antibiotic and antifungal properties. I prefer
fresh bark because it has a longer useful life in the soil mixture.
Composted or partially composted products already have one foot in the
grave when it comes to particle integrity.

It is true that any organic element in the soil uses nitrogen in the
process of breaking down, or composting. This is only a temporary
phenomenon, it is returned to the soil after the decomposition is complete.
In very lean and practically inert bonsai soil mixes this process is of
minor consequence IF one fertilizes regularly as one should anyhow for the
general health of the plant.

There is an air of mystery about this nitrogen loss phenomenon, perhaps it
will help if I explain what happens. Organic material does not break down
on its own (except for a very slow process of oxidation, which could be
measured in years). The breakdown is a composting process which requires
fungi, bacteria, and other microorganisms. These organisms are literally
eating the organic material.

When a batch of compost is properly made, it will go through several phases
of temperature increase caused by the chemical changes wrought by the
various organisms. As the temperature rises it reaches various thresholds
that represent the optimal temperatures for each species. As the optimum is
reached the favored species 'blooms', racing through and colonizing the
compost. As the temperature continues to rise the previous bloom species is
killed off andthe next species in line (that likes higher temperatures) is
favored, and then it blooms. This process continues until the internal
temperature gets close to 140F in which only a few fungi can survive and
bloom.

As each species blooms there is a massive amount of multiplication and cell
division. This can only take place if there is enough nitrogen to support
the increase in amino acids necessary for cell division. This nitrogen is
only needed as long as the composting process is taking place. Once it is
finished all the organisms are dead, cell division is over and the need for
nitrogen is over.

All the nitrogen that was incorporated into the bodies of these organisms
is now available to other creatures and plants that need it. The loss of
nitrogen was only temporary, while the organisms were growing and
multiplying. In a good compost pile the nitrogen is added for this process
in the form of manure or nitrogen salts in some cases. The nitrogen is
returned in the compost in a complex organic form that plants can readily
absorb. That is why compost is such great stuff for the garden.

If you try to compost organic material without adding additional nitrogen,
it will be a very slow process. The organisms will take nitrogen from
wherever they can get it. It you put raw carbon heavy materials into a
native soil, it will compost at the expense of the nitrogen in the soil
solution that is usually available to the plants. This is the nitrogen
lockup that everyone fears. It is easily overcome by incorporating nitrogen
into the carbon heavy material at the same time by adding manure or regular
fertilizer. Again, as the process finishes, the nitrogen will be returned
to the soil, better than ever.

All of these processes are very important for soil building in the garden,
but have very little relevance for container soils. The reason? In
container soils we strive for amendments that do NOT break down (compost).
Breakdown is associated with a decrease in particle size, which is a
critical factor in container soils. In other words, if your container soil
composts, you are in trouble because it will make the particles smaller,
the soil denser. You lose your drainage and aeration. In container growing
it is a race to get the roots to colonize the container before the soil
composts and collapses. Once the roots have colonized the container they
will literally support the soil structure and prevent it from collapsing. I
have seen root bound plants growing very happily with practically no soil,
all of it had been washed out of the container. The plant was supported by
the root network which held water by mostly capillary action.

The interaction of soil and roots in containers is a fairly complex
phenomenon and depends on a number of factors, but the principles are
relatively straight forward. For more on this subject, see the article at
my website.

http://www.evergreengardenworks.com/soils.htm





Brent in Northern California
Evergreen Gardenworks USDA Zone 8 Sunset Zone 14

http://www.EvergreenGardenworks.com

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