Crohn's Disease & Ulcerative Colitis Support Group
Crohn's disease is a systemic inflammatory bowel disease (IBD) of unknown cause, that results in chronic inflammation of the intestinal tract. It can affect the entire gastrointestinal tract from mouth to anus, and can also cause complications outside of the gastrointestinal tract. There is no known medical or surgical cure for Crohn's disease, but there are many medical...

There are some foods that I try to buy organic but not all foods, and to me whether they will help you with your UC or not is debatable. I wouldn't make yourself crazy over needing to buy organic foods solely due to UC.
Also here's some interesting info:
http://www.canadianliving.com/health/nutrition/12_foods_to_eat_only_if_theyre_organic.php
http://www.npr.org/sections/thesalt/2012/09/04/160395259/why-organic-food-may-not-be-healthier-for-you
http://www.treehugger.com/green-food/organic-and-gmos-matter-not-much-you-think.html