Anil
Absolutely, it is well documented that good container mixes should have
about 25% porosity (air space by volume). There are even simple tests
you can conduct to measure it. I could post one if anyone is interested.
The rate at which the water drains out is only an indication of
aeration. The situation is this: Water will drain from a pot of soil
until the lowest possible level of saturated soil is reached. No more
water will drain out, EVER. The height of this column of saturated soil
in the bottom of pot depends upon the nature of the soil, but mostly by
the particle size. The finer the soil, the higher the column, and thus
the greater the volume of saturated soil (and total volume of water)
retained after drainage.
Further removal of water is accomplished by transpiration of the plant
(water is absorbed by the roots and transported to the leaves). It may
not be obvious, but this is the greatest factor in removing water from
the soil, evaporation is the secondary factor.
You can do some simple experiments to test this. Saturate a common
sponge with water and place it flat on your hand until it stops
draining. Then tip it vertically, more water will drain. This is because
you have increased the height of the saturated column. It will continue
to drain until the column height is the same as the flat sponge. From
this experiment you can see that the shape of the pot will also affect
the amount of water retained. A tall pot will retain LESS water than a
low flat pot of the same volume with the same soil.
Brent
EvergreenGardenworks.com
Anil Kaushik wrote:
Brent
Thank you for the comprehensive reply. At last I got the right answer!
(Theo also said so and I think he was absolutely correct)
Also could you please tell if there are parameters regarding the porosity of
Bonsai mixture? Has anybody conducted research or study on *porosity*. If
you pour water over gravel, the water will drain out in seconds. And if you
do the same on fine grit say with 1 to 2 mm sized particles, it will still
drain out quickly. Likewise it will pass out quickly through fine sand
(dust free) or may take a little longer. How porous the Bonsai potting mix
should be for different climatic conditions? If you have some information
please share.
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