One of my favourites, sorry Debs.
It will freeze without needing to be blanched. Chop, spread on tray, freeze, bag up.
You can also freeze a celery puree. Blitz it with a whizzer thingy then put in tubs, but leave the lids off till the celery has frozen or they could burst.
Finely chopped it is good in all forms of "slaw" type salads.
Tip: to remove the strings, break a stick from inside to out then pull apart.
Don't bin it, experiment.