permaculture

[Doug-Cherry@webtv.net (Douglas Cherry)]

        Making potting compost is really a balancing act. You must  have
adequate drainage, so you add gravel and/or sand, or to save weight,
perlite or expanded polystyrene granules and yes those little spherical
pieces are "pointless". 
      You also want to retain water (hence the balancing act), so in the
soil based mixtures they add clay and loam and composted vegetable
matter. These were replaced by peat (which is of course not a renewable
resource) because it was cheap, and now by "silica gel", because it's
cheaper. I have as an experiment, grown very healthy and productive
tomato plants using water, a high potash fertilizer, and silica gel
only. As the plants draw water from the gel it shrinks (eventually back
to a crystalline form and the plants wilt) so the level of the medium
subsides. When watered again, the crystals return to their full depth by
absorbing over a hundred times their own volume in water  (OK, that may
be an exaggeration, but I'm sure I read it somewhere) and the resulting
fruits were better than shop bought. But that's not saying much. They
were however MUCH more prolific than the ones in the garden, which is!
       Although it may be possible to reuse these polymers several
times, it isn't recommended. As the plant dies at the end of the year,
diseases (from rotting roots) enter the gel. There is also a build up of
salts, not used by the plant, that are also absorbed into the gel. I
understand that tobacco mosaic virus can exist in a crystalline state
for many years, so there is also the probability of eventual build up of
other pathogens.
      Seaweed extracts (not agar, this will just encourage molds and
bacteria to grow in the soil) will not even last the growing season  and
should be reapplied every 4 to 6 weeks, but they do make a difference to
the taste of the produce, as well as the plants resistance to both
drought and insect attack. This is probably as a result of micro
nutrients.
        If you want to try growing in silica contact me off list.
Sorry for the length of this posting, I'll try to be less wordy next
time.

Doug-Cherryspam@spamwebtv.net