Joe,

If you have trays full of water, it certainly IS "true" semi-hydroponics,
you just have an external reservoir, rather than internal.

Your guess on the 30% open air space is probably high, but pretty
reasonable. If the particles were perfect spheres of uniform size, it's
about 40% open - no matter what the diameter. The more irregular the shape
and dissimilar the size of the particles, the less is open. My own
measurements with PrimeAgra many moons ago showed 26%.

--

Ray Barkalow - First Rays Orchids - www.firstrays.com
Plants, Supplies, Artwork, Books and Lots of Free Info!


"jtill" wrote in message
oups.com...
Kenni, that may be true for water holding culture, I am using SemiHydro
clay pellets that drain free water instantly and require a small sump
that holds water to provide for the wicking of water up the pot
internally, and in my case keeping the pot wet. In my use of clay pots,
which is not true SemiHydro, I need a saucer to hold that water. The
beauty of SH is that there is much air space in the culture all the way
down the pot bottom as well as damp clay to allow the roots to breath
and adsorb (or is it absorb) water and food. Someone will calculate the
free air space one day and my guess is about 30% throughtout the pot.
I may very well run into trouble with this approach but it makes sense
to me. I use RO water and very low levels of sea weed solution as a
food. I simply had to much trouble with bark, charcoal and inerts so
have switched to expanded clay. I use clay pots rather than plastic
because the wind blows my plants over in plastic. Is that enough air
circulation! ;-)) Hey, I do listen to you folk, being a newbie I need
the information and am very glad this forum and others are so free with
help and advice.
Thanks!!!
Joe T