Here is a list of spring festivals in Jeollanam-do or close to it. Please add any I missed or provide more details.
*
Yeongchuisan Jindalrae Festival - March 27 to April 10
Azalea festival on Yeongchuisan in Yeosu.
Official site*
Yeongam Wangin Cultural Festival - April 5 to April 8
In Yeongam County.
Official site*
Cheongdo Bull Fighting Festival - April 12 to April 16
Cheongdo County, Gyeongsangbuk-do.
Official site*
Hwasun Dolmen Festival - last week in April
In Hwasun county
*
Naju Pear Blossom FestivalAlways in April, but I can't find any details on it yet. I went last year and it's pretty lame, though. All the stuff at the Naju Pear Museum is in Korean, and there are only about two dozen tents set up in the parking lot (but not a whole lot to really buy, see, or do). You can walk all through the neighboring pear orchards, though, which is kind of pleasant. I think it's only worth it if you're planning to other touristy stuff in Naju. The cherry blossoms, for instance, on Namsan Park downtown are nice and are in bloom around the same time, and you can easily visitthe two big gates from there and some of the historical sites. Bus number 180 goes from the Naju Bus Terminal to the Pear Museum.
*
Jindo Sea Parting Festival - May 5 to May 7
Jindo county, a few miles from Jindo-eup.
Profile from Tour2Korea*
Damyang Bamboo Festival - May 3 to May 9
In Damyang county.
Profile from Tour2Korea*
Hampyeong Butterfly Festival and Expo - April 18 to June 1.
In Hampyeong county.
Profile from Tour2KoreaOthers:* Apparently there is a Turtleship Festival coming up in April in Yeosu, but I can't find any details on it.
* There was also a Yudalsan Flower Festival last April on Yudalsan in Mokpo. Any details for 2008? That might be a prime opportunity for me to finally visit that gangster outpost.