Yes, you need to manually clean them up because you've setup your own session save path. You can check the age of a file and delete if it's older than x days/minutes whatever:
cd /path/to/sessions; find -cmin +24 | xargs rm
Taken from the note part of php.ini:
; NOTE: If you are using the subdirectory option for storing session files
; (see session.save_path above), then garbage collection does *not*
; happen automatically. You will need to do your own garbage
; collection through a shell script, cron entry, or some other method.
; For example, the following script would is the equivalent of
; setting session.gc_maxlifetime to 1440 (1440 seconds = 24 minutes):
; cd /path/to/sessions; find -cmin +24 | xargs rm
See as well this related/duplicate question: cleanup php session files
"Single" command:
find /path/to/session -name sess_* -cmin +24 -exec rm {} \;
