Everyone needs a vacation, even musicians, and the summer is quite naturally a time that the classical music world slows down. So this is it for your Classical Music Agenda, until August. This week’s installment will be a little longer than normal, because there are several interesting things happening over the next couple months. If you want to hear some music this summer, you can, and here’s where. HEADLINES: >> The most important classical music…

Be a good son or daughter and call your mother today. Then you can start thinking about what concerts to hear this week. Maybe you can ask your mom to come with you. THE BIG GUNS: >> Joining the National Symphony Orchestra this week is Chinese pianist Lang Lang. He and composer Jennifer Higdon have parted ways about her new piano concerto, which he was supposed to premiere this week. Instead, Lang Lang will play…