Most likely they are frozen but when the servers come back online they sync back with the calendar and adapt them as if they were online while all that time passed.
Having only some things or everything frozen even after the servers come back online could do some funny things with lockouts. Especially when you consider things like some realms having extended maintenance or emergency maintenance. So while it's inconvenient it does make sense to have the servers act as if they were online during maintenance.
SE give a warning about wedding bookings but nothing about plants. An extra line about planting would be helpful.
