Heritage river birch -losing leaves and how long do they live?
I am in zone 5, NY's Hudson Valley. I have planted 4 multi trunked heritage river birches on my property, about 6 years ago. They are lovely and growing up fast and I am so happy to finally have some dappled shade around my house.
However... Every year around this time they lose about a third to half of their leaves (they yellow out and fall). They seem fine after that and come back fine each spring and grow significantly each year. No dead branches, etc. Do you think they are under some kind of stress? I do water the perennial beds around them... but not very consistently... My soil is sandy and poor, ph ~6.5. But there are beds around them and they are mulched and cow manure/top soil has been added consistently. Why do you think the leaves fall?
Secondly, how long do these trees live? Should I get some other trees started around them so they can fill in later? I do need shade where they are... I saw this question was asked before but not for this area...