My small front garden is mainly populated by pots.

Novice also wants to grow some pine trees and bamboo in these small cold
water storage tanks.

See pictu

http://tinypic.com/view.php?pic=2192hyt&s=5

These tanks are 45cm (18") x 33cm (13") x [30cm (12") high].

Since i will only water the garden about once a week, it would be ideal not
to put any drainage holes in the tank, so any rain would *all* be collected
in the pot. But since i'm afraid of causing rot in the roots, i think i
must have some drainage holes.

I have found in the past that the roots find the holes after a while and go
down into the soil, causing problems when i want to move things around at a
later date.

So what I thought I would do is put some drainage holes in the *side * of
the tank. Then I can easily see if the roots are pushing through.

The question is; how high up the side of the tank to put the holes? If i
put them up say 3 or 4 inches from the bottom, it would trap a bit of water
(like these 'so called' self watering pots).

Would that be about right? Any higher would be better in that it would
retain more water, but would it cause root rot? Grateful for any
suggestions on the best height of the holes.