By Teresamay
Suffolk,
United Kingdom 
Thankyou Bamboo, my birches are 25yrs old so extremely tall, I shall follow your advise and hose when there is no sun.
28 May, 2015
Doesn't matter whether there's sun or not for your purposes in this instance - the plants won't burn. It only matters if you're actually watering, when it doesn't make sense to water in hot sun because a lot of it evaporates straight away. I'd be flushing them daily to try to keep down the sticky build up...
28 May, 2015