I'm in town next door to a site about to be developed so I've had a
gardener put in some trees to make a screen. I believe the trees are
paper birch.

I'm sure he's very competent and seems to have made a thorough and
elaborate job of supporting the trees - about 5m tall, 5-7 cms in
diameter but between the two visits he made to finish the job he's
been inconsistent in his advice on watering.

Of course, I take it as axiomatic that watering is critical while the
trees work to establish themsleves. On this he says -

It's nigh-on impossible to over-water the trees. There will be no
risk to their health if I give them more than they need during this
first growing year.

On his first visit he recommended one watering can per tree every 2
weeks. The can he pointed to was approx 8 litres. On his second
visit he recommended 30 litres per tree per week which is almost an
8-fold increase in dosage.

Is their a reliable concensus on these two issues; quantities and risk
of overwatering?

Thanks for any input..