Growing celery- Must I tie them up or hill them?

Hi Elisa, Here's a link that may help: https://www.almanac.com/plant/celery

Good luck!

Celery needs rich loose soil with good drainage. Hills are used because the celery does not. Red much horizontal growing space, but you can grow them in rows, also. Pull it when the plant is about a foot high, roots and all. Chop off the roots and wash the celery, separating the stalks as you wash. If you are not using all the celery at once, wrap them in damp paper towels and store them in the crisper or bottom drawer of the fridge. Best wishes, Elisa! ☺️

You need to hill them or use boards against the stalks to blanch them. This turns them the nice lighter green color and improves the taste.