A U.S. foot equals about 30 cm, Susie. I'd have to look it up to be more exact. If that's not what you mean, please tell us.

Uk foot the same Tugbrethil. I still measure in old "money", yards, feet and inches, pounds and ounces and still think in pounds, shillings and pence. How sad is that.

I think Susie's 'what's a foot' should have read 'what's a-foot' in other words what is going on.

Also, are you talking about a solitary plant or the whole crop? How many stalks of celery are you talking about? Did they all mutate in this weird way or just one plant?

It has been a long time since I have grown anything other than self-blanching type celery, so I had to read up on trench celery. If I am understanding your description, Susie, it sounds like you dug too deep a trench to begin with, started the earthing process too soon, before longish stalks had started to form, and didn't earth up deeply enough in each stage. The soil that you used for earthing up may also have been too heavy with clay, which will tend to cause the central stem to elongate as it reaches for oxygen. It is also important to use a variety bred for trench growing, rather than the newer self-blanching varieties.