Why is the potting MIX better than the potting SOIL? Air space in
the growing medium.
This is why it is important (the poster being replied to is describing
the root behavior of "living mulch", but the same principles apply to
tomato roots in containers; potting MIX has a lot more air space than
potting SOIL, so does not stay water logged as long after you water or
after it rains):
http://lists.ibiblio.org/pipermail/p...ry/007522.html
A scientific explanation of the characteristics of good container mix:
http://edis.ifas.ufl.edu/cn004