How thick are the stalks, Dnk? Also, do you keep them cool and moist after harvest, and separate the leaves rightaway?

They are about 2ins thick pick a few to eat top and tail and eat straight away raw

I would pick them before they got as thick as that! You should find the younger ones are OK all the way through.

the reason they are difficult to eat is beacause as they get older and thicker they produce tougher water carrying vessels. the stringy bits that you also find in celery. You would be better picking them when they are about 1" thick.

welcome to GoY too :o)