I thought I would do this thread as I have been experimenting over the years with different watering regimes in March. The one thing I have noticed beyond anything else, is that if you fail to water in March due to having a wet Winter and especially February, then ground trees do not flourish throughout the Summer and do not give a good show in the Autumn. March is very soon upon us and here in Southern England and the long range forecast is dry for the next two weeks. So after all the experimenting, I will be watering all my ground trees in seven days time. All my water tanks and butt's are full, so I can make use of the stored rain water. But if you don't have rain water harvesting, then do think about some tap water for your maples at a time when they are going to leaf out. I have been carrying out this watering regime for the last ten years and it has served my trees well. I did miss doing this five years ago due to a holiday and I had no end of troubles with my trees for the rest of that year. I am not saying this method is what anybody else should do, but I wanted to share my results. As a footnote, do consider water butt's to collect rain water from your roofs. Potted maples really enjoy it.