Your pin actually worked for me; apparently we have few Dutch members. Do have an outdoor space to "park" your babies in during summer? If not, would weather permit doing so? Or are they always forced to stay inside and push their little leaves up against windows or door longing for freedom? I ask because figuring out your gardening zone will take some effort and might not be accurate.
I'm bowing out now; you're in good hands with the "guys" on board. BTW, you didn't mention the variety in this thread (unless I'm blind). Do you know what you have there? Or was told you have? JFYI, I don't think it's a Blue Java but what do I know?
Carry on and good luck!