Have you ever noticed that when you water a pot and the water runs out
of the bottom of the pot into a tray, you can be surprised when you
look moments later to find that the tray no longer has any water in
it? Osmosis will operate until all the soil is truly saturated.

Respect

Hussein


Osmosis doesn't operate until all the soil is saturated. Different soils will
hold differing amounts of water (Field Capacity). I think the advice I gave
was accurate given that it was general advice. To give specific advice I'd
have to know hugely more about the trees/pots involved and their position, etc.
than I do at present. The original concern was about water requirements, as
far as I can remember. If there are concerns about freezing, then that's
another point entirely.

If osmosis is going to lead to waterlogging, then you've got serious problems
with your growing medium. Most soils/growing mediums that are any good at all
will not become waterlogged when a large pot (it is a trees/trees we're talking
about here) are stood in shallow trays with a little water in. Osmosis just
isn't that efficient, and has it's limits. Unless the pot receives rain or is
watered from the top, the top layer of soil/growing medium is unlikely to be
wet, let alone waterlogged.

Watering in the way I suggested has several benefits. It doesn't wash
nutrients through the soil/growing medium and out the bottom of the pot
(leaching) as watering from above does. The plant is encouraged to send roots
downwards and should therefore have a better root structure. The plant is
unlikely to suffer from fluctuations between drought and having plenty of water
that can occur with sporadic watering.

If someone wants further details I'd be happy to answer any questions. If I
don't know about something, I don't give answers. If my answers are not
detailed enough, I'll happily give fuller explanations. A good start for
gardeners who want to better understand plants would be to invest in a copy of
Principles of Horticulture, published by Butterworth Heinemann. They have a
web site at www.bh.com. The book is very readable and easy to understand. It
explains many aspects of plant biology and soil science and I'd recommend it.

Dave.