In message , Franz Heymann
writes

"Mike Lyle" wrote in message
. com...

[snip]

I'd also guess (but it's only a guess) 40 cm is too big a pot: best
way is the old rule of patiently going up one size at a time, and
only
when the roots have definitely reached the outside of the old pot,
so
that any water you give will immediately go to the plant, rather
than
hang about going stagnant. (Some people, in this group notably
Franz,
ignore this rule without ill effect; but they have a watering regime
to suit.)

That is an urban legend. If there were any truth in it, all plants
planted in the open ground, which is an infinite sized pot for
practical purposes, should fail.

That isn't true though. The ground has usually has pretty good drainage.
A plant stuck in a pot has to rely on all the extra water escaping from
a small hole in the bottom of the pot. Block the hole and you have
stagnant water and few living things can tolerate HS (it is more
poisonous than HCN).

I grow cacti and water them like normal house plants in mid-summer but
they are planted in a very free draining grit with a small amount of
compost so they dry out between waterings.

I planted a very young Acer palmatum atropurpureum directly in a 45 cm
pot about eight years ago and have never repotted it. It thrives.

I suspect you are somewhat meagre with the watering. Then it will be OK.
Most Japanese acers grow on mountainsides and expect to be dry at the
roots from time to time.

Where I live at the moment I am having to tip water out of trays under
pots containing small trees. I am supposed to be watering them for a
neighbour but we had 100mm of rain in the last two days!

Regards,
--
Martin Brown